CHEMISTRY

Class 10th (KPK)

NAME: __________________________

F.NAME: _________________________

CLASS:___________ SECTION: ________

ROLL #: _____ SUBJECT: ____________

ADDRESS: ___________________________________

__________________________________________

SCHOOL: _____________________________________

https://web.facebook.com/TehkalsDotCom/

https://tehkals.com/
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 1

Unit 9
CHEMICAL EQUILIBRIUM
Exercise: Short Questions.
Q1. Define chemical equilibrium with two examples.
Ans: Definition: “The state of a reversible chemical reaction in which the rate of forward reaction
becomes equal to the rate of backward reaction in called chemical equilibrium/Dynamic equilibrium”.
OR The state in which both reactants and products are presents in concentration in which no further
tendency to change with time.
Examples
i. Change of a liquid to gas in a closed container:
when liquid water is placed in a closed container at constant temperature, part of liquid evaporates. As
water begins to evaporate, at the same time, some of the vapours also begin to condense. Although in
the beginning rate of evaporation is faster than the rate of condensation but with the passage of time
the rate of evaporation becomes equal to the rate of condensation and thus a state of equilibrium is
established
𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒
Water ⇄ Vapours
𝑐𝑐𝑒𝑒𝑒𝑒𝑐𝑐𝑒𝑒𝑒𝑒𝑐𝑐𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒
Equilibrium state is also in the following chemical reactions
ii. Reaction of sulphur dioxide with oxygen:2SO2 (g)+ O2 (g)⇌ 2SO3(g)

iii. Reaction of hydrogen with iodine:

H2(g)+ I2(g)⇌ 2HI(g).
Q2. How would you identify that dynamic equilibrium is established?
Ans: Chemical equilibrium/Dynamic equilibrium:
Definition:
“The state of a reversible chemical reaction in which the rate of forward reaction becomes equal to the
rate of backward reaction and the concentrations of reactants and products remain constant is called
chemical equilibrium/Dynamic equilibrium”.
Explanation:
Consider a general chemical reaction in which reactant. A reacts with reactant B in gaseous state, in a
closed container, to form products C and D.
A(g) + B(g) ⇌ C(g)+ D(g)
The detail about this general reversible reaction is given below:
i. Concentrations at the start:
At the start of the reaction the concentrations of A and B are maximum while that C and D are zero.
ii. Concentrations after some time:
With the passage of time the concentrations of C and D gradually increase while that of A and B
gradually decrease.
iii. Variation of rate of forward and backward reactions:
Change in concentrations of reactants or products per unit time is called rate of reaction.
In the beginning, the rate of forward reaction is maximum while rate of backward reaction is almost zero
but as the time passes and sufficient amounts of C and D are formed then the rate of backward reaction
increases while that of forward reaction decreases until rate of forward reaction becomes equal to the
rate of backward reaction. Thus, a state of dynamic equilibrium is established.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 2

iv. Concentration at equilibrium state:

The concentrations of reactants or products remain constant at equilibrium state. These concentrations
are called equilibrium concentrations.

Q3. Compare the different macroscopic characteristics of forward and reverse reactions?
Forward reaction Reverse reaction

It is defined as the conversion of reactants into It is defined as the conversion of products

products per unit time or the rate of chemical back into reactants per unit time or the rate of
reaction taking place in forward rection, chemical reaction taking place in forward
rection,

Characteristics

i. It is a reaction in which reactants reacts to i. It is a reaction in which product reacts to

form product. form reactants.

ii. It takes place from left to right ii. It takes place from right to left.

iii. At the beginning, rate of forward reaction is iii. At the beginning, rate of reverse reaction is
very fast. very slow.

iv. It slow down gradually iv. It speeds up gradually...

Q4: What information is required to predict the direction of chemical reaction?

Ans: Prediction of direction of reaction:
The direction of reaction can be predicted by means of [product]/ [reactants] ratio.
[𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖 𝑐𝑐𝑜𝑜 𝑝𝑝𝑐𝑐𝑐𝑐𝑝𝑝𝑝𝑝𝑐𝑐𝑖𝑖𝑝𝑝]
Qc=
[𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑝𝑝]
By comparing the ratio with Kc we have three possibilities:
When the ratio is less than kc:
if the ratio is less then Kc. The system is not at equilibrium and more product is required to reach the
equilibrium. Therefore, reaction will proceed in forward direction to form products.
When the ratio is greater than kc
If the ratio is greater than Kc The system is not at equilibrium and more reactant are required to reach
the equilibrium. Therefore, the reaction will go in the reverse direction to form reactants.
When the ratio is equal to kc
If the ratio is equal to Kc then the reaction is at equilibrium i.e. rate of forward reaction is equal to the
rate of reverse reaction.
Q5: Relate the active mass with the rate of chemical reaction?
Ans: Active mass:
Active masses are molar concentration of reacting substances. Molar concentration is the number of
moles per dm3 or litre.
Active mass and the rate of chemical reaction
The rate of a chemical reaction is directly proportional to the product of active masses of the reacting
substances.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 3

Which means when we increase the Molar concentration of reacting substances the rate of reaction also
increases and vice versa.
Q6: At equilibrium a mixture of N2, H2, and NH3 gas at 500°C is determined to consist of
0.602mol/dm3 of N2, 0.420mol/dm3 of H2 and 0.113mol/dm3 of NH3. What is the equilibrium
constant for the reaction for the reaction at this temperature?
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
Given: Concentrations of Nitrogen (N2) = 0.602mol/ d𝑚𝑚3
Concentration of hydrogen (H2) = 0.420mol/ d𝑚𝑚3
Concentrations of NH3 = 0.113mol/ d𝑚𝑚3
Required:
Value of Kc =?
Solution:
Writing equilibrium constant expression for the above reaction:
[𝑁𝑁𝑁𝑁3 ]2
Kc=
[𝑁𝑁2 ][𝑁𝑁2 ]3
[0.113𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
=
[0.602𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ][0.420𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]3
[0.012769𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
=
[0.602𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ][0.074088𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]3
[0.012769𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2 [0.012769𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
= −3 3 =
[0.602𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ][0.074088𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚 ] [0.0446𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]4
-3 -2
= 0,28630[mol/dm ]
0.28630𝑚𝑚𝑒𝑒𝑙𝑙 −2 𝑐𝑐𝑚𝑚6
Q7: State conditions necessary for the chemical equilibrium.
Ans: Conditions necessary for equilibrium:
Followings are the conditions necessary for chemical equilibrium:
i. Closed container:
Equilibrium state can only be attained in closed container. It cannot be attained in open container
because in open container the gaseous reactants and products will escape due to which there will be no
possibility of equilibrium.
ii. Constant concentrations:
When equilibrium state is attained by a reaction in a closed container then the concentrations of various
species in the reaction become constant. These concentrations are called equilibrium concentrations.
iii. Effect of catalyst on equilibrium:
A catalyst cannot change the equilibrium point, it only speedy up the rate forward and backward
reactions. Thus, it helps to attain the equilibrium in short time.
Q8. Write equilibrium constant expression for the following reactions.
a. N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
Kc for this reaction is
[𝑁𝑁𝑁𝑁3 ]2
Kc =
[𝑁𝑁2 ][𝑁𝑁2 ]3
b. 2H2 (g) + O2 (g) ⇌ 2H2O (g) Kc for this reaction is:
[𝑁𝑁2𝑂𝑂]2
Kc =
𝑁𝑁2]2 [𝑂𝑂2 ]

c. 4NH3 + 5O2 ⇌ 4NO (g) + 6H2O (g)

Kc for this reaction is
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 4

[𝑁𝑁𝑂𝑂]4 [𝑁𝑁2𝑂𝑂]6
Kc =
[𝑁𝑁𝑁𝑁3]4 [𝑂𝑂2]5

Q9. A reaction between gaseous sulphur dioxide and oxygen gas to produce gaseous sulphur
trioxide take place at 6000C. At this temperature, the concentration of SO2 is found to
1.50mol/dm3. Using the balanced chemical equation, calculate the equilibrium constant for this
system. Ans: balanced chemical equation:
2SO2(g) + O2(g) →2SO3
Solution:
Concentration of SO2 =1.50mol/dm3
Concentration of O2 =1.250mol/dm3
Concentration of SO3 =3.50mol/dm3
Find Kc =?
[𝑆𝑆𝑂𝑂3] 2
Formula = Kc=
[𝑂𝑂2 ][𝑆𝑆𝑂𝑂2 ]2
[3.50𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
=
[1.250𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ][1.50𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
12.25[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
=
2.8125[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]3
4.353[mol/dm3]-1

Q10: Describe the effect of temperature on equilibrium constant?

Ans: Effect of equilibrium constant:
Equilibrium constant is changed if we change the temperature of the system. For example, when the
forward reaction is exothermic then increasing the temperature decreases the value of equilibrium
constant. When the forward reaction is endothermic then increasing the temperature increases the value
of equilibrium constant.
LONG QUESTIONS:
1. SO3 (g) decomposes to form SO2 and O2 (g). For this reaction write,
i. Chemical equation
2SO3→ 2SO2 (g) + O2 (g)
[𝑆𝑆𝑂𝑂2] 2 [𝑂𝑂2 ]
ii. Kc expression: Kc=
[𝑆𝑆𝑂𝑂3 ]2
[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2 [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]
iii. Unit of Kc =
[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
= mol/dm3
Q2.a. Describe equilibrium state with the help of graph and an example.
Ans: Equilibrium state:
History:
Chemical equilibrium was first discovered by a French chemist Claude Louis Berthollet in 1803.
Definition:
“The state of a reversible chemical reaction in which the rate of forward reaction becomes equal to the
rate of backward reaction in called equilibrium state.
“The state of a reversible chemical reaction at which the reactants are continuously changing to products
and the products are continuously changing to the reactants back but the concentrations of reactants and
products remain constant is called chemical equilibrium/ equilibrium state.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 5

Explanation:
i. Change of a liquid to gas in a closed container:
Consider a closed container which is partially filled with a liquid at a given temperature. At the start, and
the vapour molecules are collected at the liquid surface. At the passage of time the collected gas
molecules over the liquid surface converts to liquid back (condensation starts). In the beginning rate of
evaporation is faster than the rate of condensation but with the passage of time the rate of evaporation
becomes equal to the rate of condensation and thus a state of dynamic equilibrium is established.
v. Graphical representation:

b. Define law of mass action.

Ans: Law of mass action:
History:
This law was presented by two Norwegian chemists Cato Maximilian Guldberg and Peter Waage in
1864.
Definition/Statement:
“This law states that the rate of a chemical reaction is directly proportional to the product of active
masses of the reacting substances”.
Active masses:
The term active masses mean molar concentration of reacting substances. Molar concentration is the
number of moles per dm3 or litre. The molar concentration of reacting substances is expressed by
enclosing their symbols or formulas in square brackets i.e. []
For example:
Consider the following general chemical equation.
A+B C+D
Let, [A] and [B] = molar concentrations of A and B
And [C] and [C] = molar concentrations of C and D
Now according to law of mass action: rate of forward reaction is directly proportional to the
concentration of the reactants A and B
Rf ∝ [A] [B] Rf = forward
⟹ Rf = Kf [A][B] ate
Where kf is the rate constant for the forward rection.
Similarly, for rate of reverse reaction,
Rr ∝ [C] [D] Rr = reverse
⟹ Rr = Kr[C] [D]
Where Kris the rate constant for the reverse reaction.
At equilibrium state,
Rate of forward reaction = rate of reverse reaction
Therefore, we can write,
Rf = Rr
Kf [A][B]= Kr[C][D]
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 6

Thus, it is clear that rate of reaction is proportional to the concentration of the reactants.
Q3. Derive an expression for the equilibrium constant and explain its units.
Ans: equilibrium constant:
The ratio of the mathematical product of the concentration of reacting substances called equilibrium
constant”. OR
“The ratio of the product of the concentration of the products to the product of the concentration of
reactants at equilibrium is called equilibrium constant
Denotation
It is denoted by Kc where the subscript c indicates the equilibrium concentrations of various species in
term of mole/om3 or litre.
Derivation of expression for the equilibrium constant:
Consider the following general reaction
A+B⇌ C+D
Then Kc for this reaction will be
K𝑜𝑜 [𝐶𝐶][𝐷𝐷] K𝑜𝑜
= = Kc
K𝑐𝑐 [𝐴𝐴][𝐵𝐵] K𝑐𝑐
[𝐶𝐶][𝐷𝐷]
Kc = [𝐴𝐴][𝐵𝐵]
For more general reaction Kc is written as:
aA +bB ⇌ cC+dD
[𝐶𝐶]𝑐𝑐 [𝐷𝐷]𝑎𝑎
Kc =
[𝐴𝐴]𝑎𝑎 [𝐵𝐵]𝑏𝑏
Where [A], [B],[C] and [D] represents molar concentration of reactants and products while a,b,c and d
represent the number of moles from the balanced chemical equation.
Units of equilibrium constant:
The unit of equilibrium constant is independent of pressure, concentration and catalyst depends the
equilibrium constant expression.
Q3.b How Can you predict direction of reaction for the Kc value.
Ans: Prediction of direction of reaction:
The direction of reaction can be predicted by means of [product]/ [reactants] ratio.
[𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖 𝑐𝑐𝑜𝑜 𝑝𝑝𝑐𝑐𝑐𝑐𝑝𝑝𝑝𝑝𝑐𝑐𝑖𝑖𝑝𝑝]
Qc=
[𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑝𝑝]
By comparing the ratio with Kc we have three possibilities:
When the ratio is less than Kc:
if the ratio is less then Kc. The system is not at equilibrium and more product are required to reach the
equilibrium. Therefore, reaction will proceed in forward direction to form products.

When the ratio is greater than Kc

If the ratio is greater than Kc The system is not at equilibrium and more reactant are required to reach
the equilibrium. Therefore, the reaction will go in the reverse direction to form reactants.
When the ratio is equal to Kc
If the ratio is equal to Kc then the reaction is at equilibrium i.e. rate of forward reaction is equal to the
rate of reverse reaction.
Q4.(a). Kc has different units in different reaction. Prove it with suitable examples.
Ans: Units of equilibrium constant:
The unit of equilibrium constant depends on the equilibrium constant expression. We have two cases
regarding the units of equilibrium constant:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 7

Case-1:
It may have no units if the number of moles of reactants and products are equal in the balanced chemical
equation.
Example:
H2(g) + I2(g) ⇌ 2HI (g)
Kc for this reaction is:
[𝑁𝑁𝐻𝐻]2 [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚3 ]2
Kc= = = No units
[𝑁𝑁2 ][𝐻𝐻2 ] [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ][𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]
Case-2:
It may have units for the reaction in which the number of moles of product is greater than the reactants in
a balanced chemical equation.
Example:
N2O4(g) ⇌ 2NO2(g)
Kc for this reaction is:
[𝑁𝑁𝑂𝑂2 ]2 [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
Kc= =
[𝑁𝑁2 𝑂𝑂4 ] [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]
= mol.dm-3
Case-3:
It may have units for the reaction in which the number of moles of product is less than the reactants in a
balanced chemical equation.
Example:
N2(g) + 3H2(g) ⇌ 2NH3 (g)
Kc for this reaction is:
[𝑁𝑁𝑁𝑁3 ]2 [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
Kc= 3 =
[𝑁𝑁2 ][𝑁𝑁2 ] [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ][𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]3
[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2 1 1
= = = [𝑚𝑚𝑐𝑐𝑖𝑖2
[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]4 [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2 𝑝𝑝𝑚𝑚−6 ]
Q4.(b). How can you predict the extent of reaction from the value of Kc value?
Ans: Extent of chemical reaction:
The value of Kc tells us about the extent of reaction from which quantities of reactants or products can
also be predicted.
Consider the general reaction:
aA +bB ⇌ cC+dD
[𝐶𝐶]𝑐𝑐 [𝐷𝐷]𝑎𝑎
Kc =
[𝐴𝐴]𝑎𝑎 [𝐵𝐵]𝑏𝑏
The extent of reaction depends upon the magnitude of Kc , so when
i. Kc value very small:
When the concentration of [A]and [B] is large and that of [C] and [D] is small, the equilibrium, mixture
will contain large number of reactants and small number of products. It reflects that the reaction does not
proceed appreciably in the forward direction.
ii. Kc value very large:
When the concentration of [A] and [B] is small and that of [C] and [D] is large, the equilibrium, mixture
will contain large number of products and small number of reactants. It indicates that the reaction is
completed in the forward direction
iii . Kc value neither very small nor very large (moderate):
If Kc value is neither very small nor very large then neither the forward nor the reverse reaction goes to
completion. Thus, equilibrium mixture will contain appreciable amount of product and reactants.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 8

Q5. (a). Kc expression for a reaction is given below,

[𝑁𝑁2𝑂𝑂 ]2 [𝐶𝐶𝑖𝑖2]2
Kc =
[𝑁𝑁𝐶𝐶𝑖𝑖]4 [𝑂𝑂2 ]
For this reaction write,
i. Reactants and products ii. Derive the units of Kc
Ans: Reactants and products:
Reactants: HCl4 + O2
Products: 2Cl2 + 2H2O.
ii. The units of Kc
[𝑁𝑁2𝑂𝑂 ]2 [𝐶𝐶𝑖𝑖2]2
Kc =
[𝑁𝑁𝐶𝐶𝑖𝑖]4 [𝑂𝑂2 ]
[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2 [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]2
Kc =
[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]4 [𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]
1
Kc =
[𝑚𝑚𝑐𝑐𝑖𝑖 𝑝𝑝𝑚𝑚−3 ]
Q5. (b). Explain the importance on the importance of equilibrium constant, support your answer
with examples and reasons?
Ans: Importance/applications of equilibrium constant:
The value of equilibrium constant is specific and remains constant at particular temperature. The
equilibrium constant can be used to predict:
i. The direction of chemical reaction.
ii. The extent of chemical reaction.
iv. The effect of change in conditions upon a chemical reaction in equilibrium state.
The detail is given below
1. Prediction of direction of reaction:
The direction of reaction can be predicted by means of [product]/ [reactants] ratio.
[𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖 𝑐𝑐𝑜𝑜 𝑝𝑝𝑐𝑐𝑐𝑐𝑝𝑝𝑝𝑝𝑐𝑐𝑖𝑖𝑝𝑝]
Qc=
[𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖 𝑐𝑐𝑐𝑐𝑖𝑖𝑐𝑐𝑖𝑖𝑖𝑖𝑐𝑐𝑖𝑖𝑝𝑝]
By comparing the ratio with Kc we have three possibilities:
When the ratio is less than kc:
if the ratio is less then Kc. The system is not at equilibrium and more product are required to reach the
equilibrium. Therefore, reaction will proceed in forward direction to form products.
When the ratio is greater than kc
If the ratio is greater than Kc The system is not at equilibrium and more reactant are required to reach
the equilibrium. Therefore, the reaction will go in the reverse direction to form reactants.
When the ratio is equal to kc
If the ratio is equal to Kc then the reaction is at equilibrium i.e. rate of forward reaction is equal to the
rate of reverse reaction.
2. Extent of chemical reaction:
The value of Kc tells us about the extent of reaction from which quantities of reactants or products can
also be predicted.
Consider the general reaction:
aA +bB ⇌ cC+dD
[𝐶𝐶]𝑐𝑐 [𝐷𝐷]𝑎𝑎
Kc =
[𝐴𝐴]𝑎𝑎 [𝐵𝐵]𝑏𝑏
The extent of reaction depends upon the magnitude of Kc , so when
i. Kc value very small:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 9

When the concentration of [A} and [B] is large and that of [C] and [D] is small, the equilibrium, mixture
will contain large number of reactants and small number of products. It reflects that the reaction does not
proceed appreciably in the forward direction.
ii. Kc value very large:
When the concentration of [A} and [B] is small and that of [C] and [D] is large, the equilibrium, mixture
will contain large number of products and small number of reactants. It indicates that the reaction is
completed in the forward direction
iii. Kc value neither very small nor very large (moderate):
If Kc value is neither very small nor very large then neither the forward nor the reverse reaction goes to
completion. Thus, equilibrium mixture will contain appreciable amount of product and reactants.

3. The effect of change in external conditions:

Once a system has attained the equilibrium it will remain in the same state indefinitely, if the condition
does not change. However, the equilibrium state of a system is disturbed if external conditions are
changed i.e. concentration, pressure, temperature. Changing these conditions will disturb the
equilibrium. Whenever the equilibrium is disturbed by changes in the external conditions, the system
always tends to restore equilibrium.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 10

Topic wise questions

Q1. What are irreversible and reversible reactions?
Ans: Irreversible reactions:
“Those chemical reactions which proceed in forward direction only are called irreversible reactions”.
Or”Those chemical reactions in which reactants are changed into products only and products are not
changed to reactants are called irreversible reactions”.
Characteristics of irreversible reactions:
Irreversible reactions have the following characteristics:
i. These reactions proceed in one direction only.
ii. They are represented by a single arrow sign ( )
iii. No equilibrium state is established in irreversible reactions.
iv. These reactions go to completion.

Example:
A few examples of irreversible reactions are given below:
i. Reaction of carbon with oxygen:
C(S)+O2 (g) C O2 (g)
Ii.Reaction of magnesium with HCl:
Mg(g) + HCl(g) MgCl2(s)+ H2(g)
Reversible reactions:
Those chemical reactions which proceed both in forward and backward directions are called reversible
reactions”.
Characteristics of reversible reactions:
A reversible reaction has the following characteristics:
i. These reactions proceed in two directions i.e. forward and backward.
ii. These reactions never go to completion i.e. the reactants are not fully converted into products.
iii. Their reversibility can exist in closed containers only.
iv. A state of dynamic equilibrium is established in all reversible reactions.
v. These reactions are represented by double arrow sign (⇌ ).
Examples:
Following are a few examples of reversible reactions:
i. Reaction of nitrogen with hydrogen:
N2 (g)+3H2(g)⇌ 2NH3(g)
At the start reaction goes in forward direction but as soon as soon amount of ammonia is formed, the
ammonia molecules dissociate to nitrogen and hydrogen. Thus, the reaction is reversed.
Some other examples are:
ii. Reaction of Sulphur dioxide with oxygen:
2SO2(g)+ O2(g)⇌ 2SO3(g)

H2(g)+ I2(g) ⇌ 2HI(g)

Q2.How can equilibrium constant be recognize:

Ans: in order to recognize the equilibrium constant of chemical reactions, following methods can be
used:
I: Physical method: it includes Refractometry, polarimetry, Spectrophotometry etc.
ii. Chemical methods: such as titration.
CHEMISTRY
Class 10th (KPK)

NAME: __________________________

F.NAME: _________________________

CLASS:___________ SECTION: ________

ROLL #: _____ SUBJECT: ____________

ADDRESS: ___________________________________

__________________________________________

SCHOOL: _____________________________________

https://web.facebook.com/TehkalsDotCom/

https://tehkals.com/
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 11

UNIT 10
ACIDS, BASES AND SALTS
SHORT QUESTIONS:
Q1. When a clear liquid is placed in a beaker. How can you identify whether it as an acid, base or
neutral?
Ans: Different methods is used to determine the whether the given solution/ liquid is acidic, basic or
neutral.
Litmus paper:
One of them is litmus paper test. In this method litmus paper is dipped in a beaker. If it turns the blue
litmus paper to red then the given liquid will be acidic. If it turns red litmus paper then the given liquid
will be basic. If the litmus paper remains unchanged it will be neutral liquid.
pH scale:
We can also use pH scale to measure the acidity or basicity of a solution. pH scale is a number from 0 to
14. From 0 to 7 are acids. From 7 to 14 are bases while if a liquid has a pH of 7. It will be neutral
Q2.justify H+ ion as a Lewis acid?
Ans: H+ ion as a Lewis acid:
According to Lewis concept a positively charged ions that can accept an electron pair can act as Lewis
acid.
As H+ is positively charged ion and it has tendency to accept lone pair of electrons so it acts as a Lewis
acid.
H+ + :NH3 ⟶ NH4+
(Acid) (Base) (Ammonium ion)
Q3. Distinguish strong acids from weak acids? Give two example of each.
Strong acid:
Those acids which ionizes completely in aqueous solutions and give higher concentration of H+ ions are
called strong acids”. A strong acid is strong electrolyte.
HCI, H2SO4 and HNO3 are the examples of strong acids because they completely ionize in water.
HCI (aq)⟶ H+ + CI-
H2SO4 (aq)⟶ H+ + SO4-
HNO3 (aq)⟶ H+ + NO3-
Weak acids:
“Those acids which do not completely ionize in aqueous solutions and give lower concentration of H+
ions are called weak acids”. A weak acid is weak electrolyte.
Examples:
CH3COOH (aq) ⇌ H++ CH3COO-
Acetic acid (CH3COOH) is a weak acid because when it is added into water, very few molecules of
CH3COOH are dissociated. Some other weak acids are H2S, H2CO3, H2SO3 and HNO2 etc.
Q4. Compare the physical properties of acid and bases.
Ans:
Acids Bases

i. Acids have sour taste i. Base have bitter taste

ii. It turns blue litmus paper to red. ii. It turns red litmus paper to blue
iii. Acids produce H+ ions when iii. Base produces OH- \ when
dissolved in water. dissolved in water.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 12

iv. Acids solution have PH values less iv. Basics solution have PH values
than 7. greater than 7.

Q5 A carbonated drink has [H+] = 3.2 × 10-3 M, classify the drink as neutral acidic or basic with
reason.
Ans: Solution:
Data: hydrogen ion concentration = [H+] = 3.2 × 10-M
Determination of PH
PH = -log [H+]
Putting the value of [H+] we get:
PH = - log [3.2x10-3]
=PH=-(log3.2+log10-3) ∵ log mn = logm + logn
=PH=-[log3.2-log10-]3
=PH= - (0.5051) –(-3) log 10 ∵ logmn = n log m
=PH = - 0.5051 + 3log10
=PH= -.0.5051 +3 (1) ∵ log10=1
=PH= 0.5051 +3
=PH= 2.49
As the pH is less than 7 so the carbonated drink is acidic solution.
OR
We can also solve this problem by comparing the given [H] + of the solution with that of neutral water.
As we know that [H]+ = [OH]- = 1×10-7
If [H ]+ ˃ 1×10-7 the solution will be acidic.
If [OH] - ˃ 1×10-7 the solution will be basic.
As in the given solution [H] += 3.2×10-3 M ˃ 1×10-7 the solution is acidic.
Q6. Write the chemical name of an acid present in the following.
Ans: (a). Apple juice: Malic acid
(b).Grape: Tartaric acid
(c). Lemon juice: Citric acid
(d). Sour milk: Lactic acid.
Q7.What determine the strength of a base? Give one example of each solution of strongly acidic
and weakly acidic.
Ans: Strong bases:
“Those bases which completely dissociate in aqueous solution and give a higher concentration of OH-
are called strong bases”.
Strong bases completely ionize in water and almost no unionized molecule is left behind.
Examples:
Examples of some of the strong bases are given below:
NaOH (aq)⟶ Na+ OH-
KOH (aq) ⟶ K+ + OH-
LiOH (aq)⟶ Li + OH-
Weak bases:
“Those bases which do not dissociate completely in aqueous solution and give a lower concentration of
OH- are called weak bases”.
Examples:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 13

Some bases which do not completely ionize in water are given below:
NH4OH (aq)⇌ NH4+ + OH-
Ba(OH)2(aq) ⇌ Ba+2+2OH-
Mg(OH)2(aq)⇌ Mg+2+20H-
Q8. Calculate the pH and pOH of O.5 M solution of HCl.
Calculate the PH and POH of 0.5M HCL solution.
Given:
Molarity of hydrochloric acid (HCI) solution= 0.05M
Required:
To calculate the PH and PH
Solution:
Chemical equation for ionization of hydrochloric acid is:
HCI → H+ + CI-
0.5M 0.05M
5
Hydrogen ion concentration [H+] = 0.5 = = 5x10-1 M
10
Determination of PH
PH = -log [H+]
Putting the value of [H+] we get:
PH = - log [5x10-1]
=PH=-(log5+log10-1) ∵ log mn = logm + logn
=PH=-log5-log10-1
=PH= - (.06989) – (-1) log 10 ∵ logmn = n log m
=PH = - 0.6989+1log10
=PH= -.06989 +1 (1) ∵ log10=1
=PH= -.06989 +1
=PH= 0.301
Determination of POH:
We know that:
PH + POH = 14
POH = 14 - PH
Putting the value of PH we get:
POH = 14-0.3o1
⟹POH = 13.
Result:
PH = 0.301 and POH = 13.69
Q9. Calculate the PH and POH of 0.005M H2SO4 solution.
Given:
Molarity of H2SO solution= 0.005M
Required:
To calculate the PH and PH
Solution:
Chemical equation for ionization of nitric acid is:
H2SO → 2H+ + SO4-2
0.005M 0.005M
5
Hydrogen ion concentration [H+ ]:0.005 = = 5x10-3 M
1000
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 14

Determination of PH
PH = -log [H+]
Putting the value of [H+] we get:
PH = - log [5x10-3]
=PH=-(log5+log10-3) ∵ log mn = logm + logn
=PH=-log5-log10-3
=PH= - (.06989) – (-3) log 10 ∵ logmn = n log m
=PH = - 0.6989+3og10
=PH= -.06989 +3 (1) ∵ log10=1
=PH= -.06989 +3
=PH= 2.301

Determination of POH:
We know that:
PH + POH = 14
POH = 14 - PH
Putting the value of PH we get:
POH = 14- 2.301
⟹POH = 11.699
Result:
PH = 2.301 and POH = 11.699
10. Calculate the PH of 0.2M NaOH solution?
Given:
Concentration of NaOH solution = 0.2M
Required:
POH =?
Solution:
Chemical equation for ionization of sodium hydroxide is:
NaOH → Na+ + OH-
0.2M 0.2M
1
Hydroxide ion concentration [OH-]: 0.2M = = 10-1M
10
Determination of POH
POH = -log [OH-]
Putting the value of [OH-] we got:
POH = - log [2x10-1]
POH =-(log2+log10-1) ∵ log mn = logm + logn
POH =-log5-log10-3
POH = - (0.301) –(-1) log 10 ∵ logmn = n log m
POH = - 0.301+ 1 log10
POH = -.0.301+1 (1) ∵ log10=1
POH = 0.699
Determination of PH:
We know that:
PH + POH = 14
PH = 14 – POH
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 15

Putting the value of PH we get:

PH = 14- 0.699
⟹PH = 13.301
Result:
PH = 13.301 and POH = 0.699
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 16

LONG QUESTIONS:
Q1, (a). What is salt?
Salt:
“The substance obtained due to neutralization reaction of an acid base reaction is called salt”.
Composition of salt:
A salt consists of positive ions combined with negative ions. Positive ions come from a base while
negative ions come from an acid i.e. In NaCI Na+ is from NaOH while CI- is from HCI.
Examples of some salts:
Examples of salts are given below:
ii. Silver bromide (AgBr)
iii. Potassium sulphate (K2SO4)
iv. Ferric phosphate (FePO4).
Q1. (b). write down the different types of salts with example?
Ans: Types of salts:
There are three types of salts i.e. neutral salt, acidic salts and basic salts their detail is given below:
i. Neutral salts:
“The salts formed when hydrogen atom of an acid is completely replaced by a metal ion or group of
atoms behaving like metal ion are called normal salts”.
Neutral salts are formed when a strong acid react with strong base.
Examples:
NaOH + HCI →NaCI + H2O
Base Acid Normal Salt
Some other examples of normal salts are given below:
i. Potassium sulphate (K2SO4)
ii. Sodium phosphate (Na3PO4)
iii. Ammonium sulphate [(NH4)2SO4]
iv. Sodium carbonate (Na2CO3)
ii. Acidic salts:
“The salts formed when hydrogen atom of a polyprotic acid is partially replaced by a metal ion or group
of atoms behaving like metal ion are called acidic salts”.
Examples:
H2SO4 + KOH →KHSO4 + H2O
These acids can further react with bases forming neutral salt
KHSO4 + KOH →K2SO4 + H2O
Some other examples of acidic salts are given below:
i. Ammonium bi phosphate [NH4) H2PO4]
ii. Potassium bicarbonate (KHCO3)
ii. Sodium bicarbonate [(NaHCO3] etc.
iii. Basic salts:
“The salts formed when hydroxide ions (OH-) of a base are partially neutralized by an acids are called
basic salts”.
Basic salts are formed by poly acid bases only e.g.
Examples:
Pb(OH)2, Mg(OH)2, AI(OH)3 etc.
Pb(OH)2 + HCI →Pb(OH)CI + H2O.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 17

Q2. (a). Define the auto-ionization of water. How can you find the pH of Water?
Ans: Auto-ionization of water:
The reaction in which two water molecules produce ions is called as the self-ionization or auto-
ionization of water.
Explanation:
In order to understand the concept of self-ionization or auto ionization of water, we take one molecule of
water and its dissociation at 250C, as
H2O(l) →H+(aq) + OH-(aq)
Equilibrium constant expression for this reaction is:
�𝑁𝑁 + ] [𝑂𝑂𝑁𝑁 − ]�
Kc= [𝑁𝑁2 𝑂𝑂]
As concentration of H2O remains constant and the above equation can be written as:
Kc [H2O] = [H+] [OH-]
Kw = [H+] [OH-]
where Kw= Kc [H2O]
Dissociation constant of water (Kw):
Kw is called dissociation constant or ionization constant of water. It is defined as “ the product of molar
concentration of H+(H3O+) and OH- ions is called dissociation constant of water”. The value of Kw of
water at 250C is 1.0x10-14 i.e.
Kw = [H+] [OH-] =1x10-14 mol/dm3 of water at 250C
As one molecule of water produces one H+ and oneOH- ion on dissociation.
Therefore, we can say that,
[H+] [OH-] = 1x10-14
[H+] = [OH-]
Or [H+] [H+] = 1x10-14
(H+)2 = 1x10-14
(H+)2 = 1x10-14
Therefore
(H+)= 1x10-7
And [OH-] = 1.0× 10-7
In water at 250C, (H+)= 1x10-7Mand [OH-] = 1.0× 10-7M
Kw = [H+] [OH-]
Kw = 1x10-7M × 1x10-7M
Kw = 1x10-14 M2
pH Definition:
PH can also be defined as:
“The negative logarithm of molar concentration of H+ ions is called PH”.
PH = -log [H+]
PH of Water:
According to this scale, pH of water is calculated as,
pH = -log [H+]
putting values of [H+],
pH = -log[1.0× 10-7]
pH = - (-7.0) log10 log10= 1
pH = 7.0
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 18

Q.2(b). Why some acids are called monoprotic, diprotic and polyprotic acids. Explain your answer
with suitable examples.
Ans: Acids can be classified in term of number of protons that can be given by per molecule of an acid
when added to water. Acids are classified as,
i. Mono-protic acids
ii. Poly-protic acids
Monoprotic or monobasic acids:
“Those acids which give one proton per molecule are called monoprotic acids or monobasic acids”.
Examples:
HCI, HNO3, CH3COOH, HBr, HCN etc are some of the examples of monoprotic acids because they give
only one portion per molecule.
HCI (aq)⟶ H+ + CI-
HNO3 (aq) ⟶ H+ + NO-
CH3COOH (aq)⟶ H++CH3COO-
HBr (aq)⟶ H++ Br-
HCN (aq)⟶ H+ + CN-
Polyprotic acids:
“Those acids which give more than one proton per molecule are called polyprotic acids or polybasic
acids”.
These are further divided into the following subgroups:
i. Diprotic acids:
“Those acids which give two protons per molecule are called diprotic acids or dibasic acids”.
Examples:
H2SO4H2CO3 etc. are the examples of diprotic acids because they give two protons per molecule.
H2SO4 (aq)⟶ 2H+ + SO-2
H2CO3 (aq) ⟶ 2H+ + CO3-2
ii. Triprotic acids:
“Those acids that give three protons per molecule are called Triprotic acids or tribasic acids”.
Example:
Phosphoric acid is an example of triprotic acid as clear from the following chemical equation:
H3PO4(aq)⟶3H+ + PO4-2
Q3. (a). Discuss the concept of lewis acids and bases with examples.
Ans: The Lewis concept:
Introduction:
G.N Lewis presented his own concept of acids and bases in 1923.
Definitions of acids and bases:
Acids:
According to this concept an acid is a species that can accept an election pair.
Base: Base is a species which can donate electron pair.
An acid is electrophile (electron loving) while a base is a nucleophile (nucleus loving).
Species which acts as Lewis acids:
Those compound in which central atom has less than eight electrons in valance shell or positively
charged ions that can accept an electron pair act as Lewis acids. e.g. BF3, AICI3,H+ etc.
Species which acts as Lewis Base:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 19

Those compounds in which central atom has lone pair of electrons in valance shell or negatively charged
ions that can donate an electron pair can act as Lewis bases. act as Lewis bases e.g. NH3, H2O,CN-,CI-

Example:

Q3. (b) Give the bronsted-lowery definition of acids and bases. Write equation that explain the
definition.
Ans: Introduction:
Bronsted and Lowry presented a broader concept about acids and bases in 1923.
Definitions of acids and bases:
According to Bronsted-Lowry concept.
Acids: Acids are defined as the substances which donate or tend to donate protons (H+ ions).
Bases: Bases are defined as the substances which accept or tend to accept protons.
Examples:
i. When ammonia (NH3) is added to water, the following reaction occurs:
+
HCl (aq) + NH3 (aq)⟶ N𝑯𝑯𝟒𝟒(𝒂𝒂𝒂𝒂) + Cl-(aq)
(Acid) (Base)
In the above example the ammonia accepts a proton from HCI, therefore, it acts as a base while HCI
donates a proton and therefore it acts as an acid.
ii.HCl + H2O ⟶ H3O+ + Cl-
Acid Base
In this example water act as a bronsted-lowery base and HCl act as bronsted-lowery acid?
+
iii. H2O (l) + NH3 ⟶ N𝑯𝑯𝟒𝟒(𝒂𝒂𝒂𝒂) + OH
In the above example the ammonia accepts a proton from H2O, therefore, it acts as a base while H2O
donates a proton and therefore it acts as an acid.
Q4. Below are two equations showing how two alkalis react with water.
NaOH (aq) + H2O (i) ⇌ Na+ (aq) + OH-
NH3 (aq) + H2O ⇌NH4+ (aq) + OH-(aq)
A). name both alkalis.
Ans: NaOH = sodium hydroxide
NH3 = ammonia
B. which is classified as weak alkali and why?
NaOH is a strong base while NH3 is weak base.
c. What is the likely pH of each alkali?
PH of NaOH is13 while that of NH3 is 11.6
Q5. Write the balanced neutralization reaction of,

i. Strong acid and strong base:

 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 20

HCl + NaOH → NaCl+ H2O

(Acid) (Base)

ii.Strong acid with weak base:

HCl + NH4OH → NH4Cl + H2O

iii.weak acid and strong base:

CH3COOH + NaOH → CH3COONa + H2 O

iv.weak acid and weak base:

CH3COOH + NH4OH → CH3COONH4 + H2 O

Q5.(b). Define pH and pOH.

Ans: Meaning of P in pH and pOH
P stands for potenz (potential to be). Thus, PH means potential of H+ ions while pOH means potential of
OH+ ions while it denotes negative log i.e.=-log.
pH Definition:
PH can also be defined as:
“The negative logarithm of molar concentration of H+ ions is called PH”.
PH = -log [H+]
According to this scale, pH of water is calculated as,
pH = -log [H+]
putting values of [H+],
pH = -log[1.0× 10-7]
pH = - (-7.0) log10 log10= 1
pH = 7.0
pH Definition:
pOH can also be defined as:
“The negative logarithm of molar concentration of OH+ ions is called poH.
pOH = -log [OH+]
According to this scale, pOH of water is calculated as,
pOH = -log [OH+]
Putting values of [OH+],
pOH = -log[1.0× 10-7]
pOH = - (-7.0) log10 log10= 1
pOH = 7.0
Comparison of pH values:
A solution having PH value of 7 is neutral, less than 7 is acidic while a solution having PH value more
than 7 is basic.
Q6. (a). According to your understanding which one is the three acid definitions is the broadest?
Explain.
Ans: The three basic definitions of acid and bases are as follow;
1. The Arrhenius concept (The classical concept):
Introduction: The first concept about acids was presented by Arrhenius in 1884.
Definitions of acids: According to this concept acids are defined as follows:
Acid:” The compound which gives H+ ions in water is called acid”.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 21

Examples of Arrhenius acids:

HCI, H2SO4, HNO3, HBr, HI, CH3COOH etc. are some of the examples of Arrhenius acids because
when these are added to water, they ionize to give H+ ions which react with water to form hydronium
ions H3O+. The chemical equations for the ionization of some acids are as follows:
HCI(aq) + H2O(I)⟶ H3O+(aq)+CI(aq)
HNO3(aq)+H2O(I)⟶ H3O+(aq)+NO3-(aq)
Introduction:
Bronsted and Lowry presented a broader concept about acids in 1923.
Definitions of acid:
According to Bronsted-Lowry concept.
Acids: Acids are defined as the substances which donate or tend to donate protons (H+ ions).
Examples:
i. When ammonia (NH3) is added to water, the following reaction occurs:
+
HCl(aq) + NH3(aq)⟶ N𝐻𝐻4(𝑖𝑖𝑎𝑎) + Cl-(aq)
Proton donor Proton acceptor
(acid) (base)
In the above example the ammonia accepts a proton from HCI, therefore , It acts as a base while HCI
donates a proton and therefore it acts as an acid.
The Lewis concept:
Introduction:
G.N Lewis presented his own concept of acids and bases in 1923.
Definitions:
According to this concept an acid is a species that can accept an election pair.
An acid is electrophile (electron loving)).
Species which acts as Lewis acids:
Those compound in which central atom has less than eight electrons in valance shell and positive ions
act as Lewis acids i.e. they accept electron pair e.g. BF3, AICI3, H+ etc.
Q6.(b). Write the uses of any three salts.
Ans: Uses of salts:
i. Sodium carbonate (Na2CO3):
Sodium carbonate (Na2CO3) is called soda ash or washing soda. It is used as cleaning agent in
laundries and as water softener. It is also used as raw material in the manufacture of glass. It is also
used in paper industry, leather industry and petroleum refining industry.
ii. Sodium bicarbonate (NaHCO3):
It is also called as baking soda because it is used in baking of cakes and other confectionaries. It is also
as antacids in medicines and in toothpastes etc.
iii. Copper sulphate (CuSO4.5H2O)(Blue vitriol):
It is used as electrolyte in copper electroplating process. It is also used to kill algae in water reservoirs
and in agric substancriculture spray.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 22

TOPIC WISE QUESTIONS

Q. What are amphoteric substances?

Ans: Amphoteric substances:
“Those substances which can act both as an acids and a base are called amphoteric substances”.
Examples:
i. Water is amphoteric because it acts as a base with an acid while it acts as an acid with a base.
HCI + H-OH ⟶ H3O+ + CI-
Acid Base conjugate acid conjugate base
NH3 + H2O ⟶ NH+ + OH-
Base Acid conjugate acid conjugate base
ii. During self-ionization of water some water molecules acts as an acid while some acts as a base:
H2O + H2O⟶ H3O+ + OH-
Acid Base conjugate acid conjugate base.
Q. What is neutralization reaction?
Ans: Neutralization:
“The reaction of an acid with a base to form salt and water is called neutralization reaction”.
Explanation with example:
For example, when HCL reacts with NaOH, NaCI and water and formed.
HCI + NaOH → NaCI + H2O
Acid base salt water
In order to understanding the process of neutralization, we need to write the acid, base and salt in their
ionic forms.
H+ + CI- + Na+ + OH-→ Na+ + CI- + H2O
In solution HCI exist as H+ or H3O+ and CI-, and NaOH exist as Na+ and OH-. In neutralization H+
reacts with OH- to form water, leaving Na+ and CI- ions in the solution which are present on both sides
of the equation and they have not reacted. They are called spectator ions.
Thus, the net reaction of neutralization is the reaction of H+ with OH- to form water as given below:
H++ OH-→ H2O
The Na+ and CI- ions remain in the solution and can be obtained by evaporation the solution.
Q. Write down different method of preparation of salts?
Preparation of Salts:
Various preparation methods of salts are given below:
i. By neutralization reaction:
One of the most important and common method of preparation of salt is neutralization reaction in which
an
acid reacted with a base to form salt and water
NaOH + HCI → NaCI+H2O
Base Acid salt water
ii. By the reaction of acid and metal (Direct displacement method:
In this method H+ of an acid is replaced by the reactive metal to produce respective salt and hydrogen
gas. For example, magnesium (Mg), Calcium (Ca), Zinc (Zn) etc
2HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)
iii. By the reaction of acids with carbonates and bicarbonate
When an acid reacts with carbonate such as sodium carbonate (Na2CO3) or bicarbonate such as sodium
bicarbonate (NaHCO3) it produces salts e.g.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 23

Na2 CO3 + 2HCI →2NaCI + CO2 +H2O

NaHCO3 + HCI →NACI + CO2+H2O
iv. By the reaction of an acid and metallic:
The metallic oxide such as copper oxide (CuO), Calcium oxide (CaO), react with acids to form salt and
water.
H2SO4(aq) + CaO(aq) → CaSO4(aq) + H2O(l)
Q.What are double salts?
Ans: Double salts:
Definition:
“The type of salts which consist of two specific salts containing water of crystallization are called double
salts”.
Preparation:
Double salts are formed by mixing the saturated solutions of two specific salts in a simple mole ratio,
followed by crystallization. Double salts crystallize out containing water molecules in them. These water
molecules are called water of crystallization.
Examples:
Following are some of the examples of double salts:
Salt name Chemical formula

Potash alum K2SO4, AI2 (SO4)3, 24H2O

Chrome alum K2SO4, Cr2 (SO4)3, 24H2O

Ferric alum (NH4)2SO4,Fe2(SO4)3, 24H2O

Q. Describe the uses of salts?

Ans: Uses of salts:
Salts have many different uses, ranging from household to big industries. Some important uses of
different salts are given below:
i. Sodium chloride (NaCI):
It is daily used in our food to give it taste. It is used for seasoning and preserving food. In industry it is
used as basic raw material for the extraction of sodium preparation of caustic soda (NaOH), washing
soda etc. one of the major applications of sodium chloride is de-icing of roadways in sub-freezing
weather.
ii. Calcium sulphate (CaSO4. 2H2O):
It is also called gypsum. It is used as fertilizer in the preparation of plaster of Paris, and in cement
industry.
iii. Sodium carbonate(Na2CO3):
Sodium carbonate (Na2CO3) is called soda ash or washing soda. It is used as cleaning agent in
laundries and as water softener. It is also used as raw material in the manufacture of glass. It is also
used in paper industry, leather industry and petroleum refining industry.
iv. Sodium bicarbonate (NaHCO3):

It is also called as baking soda because it is used in baking of cakes and other confectionaries. It is also
as antacids in medicines and in toothpastes.
v. Copper sulphate (CuSO4.5H2O) (Blue vitriol):
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 24

It is used as electrolyte in copper electroplating process. It is also used to kill algae in water reservoirs
and in agriculture spray.
vi. Magnesium sulphate (MgSO47H2O) (Epsom Salt):
It is used as antacid and laxative in medicines. It is also used in dye industries.
vii. Potash alum (K2SO4.AI2 (AO4)3, 24H2O):
It is used for water purification to remove suspended impurities. It is also used in textile industry and
as blood coagulant in small injuries.
viii. Potassium nitrate (KNO3):
It is used as a fertilizer and for the manufacture of flint glass.
ix. Calcium Carbonate (CaCO3):
It is used in the preparation of cement and in ceramics industry.
x. Sodium sulphate:
It is used in the manufacture of paper, detergents and glass etc.
CHEMISTRY
Class 10th (KPK)

NAME: __________________________

F.NAME: _________________________

CLASS:___________ SECTION: ________

ROLL #: _____ SUBJECT: ____________

ADDRESS: ___________________________________

__________________________________________

SCHOOL: _____________________________________

https://web.facebook.com/TehkalsDotCom/

https://tehkals.com/
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 25

UNIT 11
ORGANIC CHHEMISTRY
SHORT QUESTIONS
Q1. Define functional group? Give example of functional groups containing oxygen.
Ans: Functional group:
A functional group is an atom or group of atoms attached with R that is responsible for the specific
properties of an organic compound.
Explanation: A functional group is the active part of an organic compound. Most of the organic
compounds consist of two parts i.e.
i. The hydrocarbon part which is an alkyl group/
ii. The functional group part.
For example:
In methanol (CH3-OH),-CH3 is the alkyl group (R) while –OH is the functional group part.
Example of functional groups containing oxygen:
Examples:
The functional groups containing oxygen are given in the table below:
Functional group Name of the classes Examples Name of
compound

-OH Alcohols CH3-OH Methyl alcohol

-CHO Aldehydes CH3-CHO Ethanal

-CO- Ketones CH3-CO-CH3 Propanone

-COOH Carboxylic acids CH3-COOH Ethanoic acid

-O-R Ether CH3-O-CH3 Di methyl ether

Q2. How can we obtain the organic compounds from natural sources?
Ans:
Q3. What are cycloalkanes?
Ans: Cyclic alkanes:
“The type of alkanes in which the carbon atoms are arranged in cyclic form are called cyclic alkanes or
cyclo-alkanes.
General formula:
Cycloalkanes have two less hydrogen atoms than in corresponding alkanes.
These have the general formula similar to alkenes i.e. CnHn2
Examples:

Q4. Write down examples of three unsaturated hydrocarbons with structural and condensed
formulae?
Ans: Unsaturated hydrocarbons:
“The hydrocarbons containing at least one carbon-carbon double or triple bond are called unsaturated
hydrocarbons”.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 26

Examples of unsaturated hydrocarbons:

Examples Structural condensed formulae
formulae

1. Ethene CH2 =CH2

2. Propene CH2 =CHCH3

3. Butene CH2 =CHCH2CH3

Q5. Define hydrocarbons, and briefly discuss their importance?

Ans: Hydrocarbons:
The compounds of carbon and hydrogen are called hydrocarbons”.
Classification of hydrocarbons: Hydrocarbons are classified into two main groups:
Saturated hydrocarbons (alkanes)
Unsaturated hydrocarbons (alkenes and alkyne)
Importance of hydrocarbons:
Hydrocarbons are most important natural resources. They are used as electric and heat energy because
they produce a large amount of heat when burned. Hydrocarbons are the main constituents of
petroleum and natural gas. The gasoline that serves as fuel for automobiles consists of hydrocarbons.
Natural gas mainly consists of methane and ethane and is used for heating and cooking purposes.
Beside fuel hydrocarbons are also used as fragrances, detergents, medicines and many other things.
Q6. How alkyl radicals are formed. Discuss with examples.
Ans: Alkyl radical/group:
“A radical or group of atoms obtained by removing one hydrogen atom from an alkane is called alkyl
group”.
General formula: The general formula of alkyl radical is CnH2n+1, where n is the number of carbon
atoms i.e. 1,2,3,4 etc
General Symbol: Alkyl radical are denoted by a general symbol-R.
Naming an alkyl radical: Alkyl radicals are named by replacing-ane of corresponding alkane by-yl.
Examples:
Number of Name of formula Name of Alkyl formula
C-atoms alkane (CnH2n+2) (CnH2n+1)
Radical

1 Methane CH4 Methyl CH3

2 Ethane C2H5 Ethyl C2H5

3 Propane C3H8 Propyl C3H7

4 Butane C4H10 Butyl C4H9

 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 27

5 Pentane C5H12 Pentyl C5H11

Q7. List some uses of organic compounds.

Ans: Uses of organic compounds: The things we use in our daily life are mostly organic compounds
such as the food we eat, the clothes we wear etc.
Our dependence on organic compounds is increasing day by day. It has changed our life style.
1: Uses of as food: The food we eat in our daily life such as milk,meat,egg,vegetables etc. consists of
carbohydrates,proteins,vitamins,fats etc. Which are all organic compounds.
2: Uses as clothing: The clothes we wear are made up of fibres.These fibers are either natural such as
cotton, silk, wool etc or synthetic fibers such as nylon, polyester and acrylic etc. All these are organic
compounds.
3: Uses as medicine: Most of the medicines that we use are organic compounds. These are naturally
synthesized from plants and are used as medicines. Most of the lifesaving drugs such as antibiotics,
anti-inflammatory, anti-malarial etc. are synthesized in the laboratory.
4: Uses as fuel: The fuels which we use, such as petrol, diesel oil, compressed natural gas (CNG), coal
and natural gas are organic compounds.
5: Uses as chemical materials: The chemicals that we use such as rubber, paper, ink, plastic, fibers,
fertilizers, pesticides, insecticides, cosmetics, paints, detergents etc. are all organic compounds.
6: Uses as life molecules: Thousands of organic molecules are taking part in our body functions.
There are four main groups of organic molecules that are carbohydrates, proteins, lipids and nucleic
acid that combine to build cells and their parts. These molecules are called life molecules.
Q8: Give the general formula of the following homologues series?
Ans:
a. Alkanes CnH2n+2

b. Alkenes CnH2n

c. Alkynes CnH2n-2

Q9. Why organic compounds are volatile in nature?

Ans: Organic compounds are volatile due to the following reason.
Reason: Volatile are those substances which easily evaporate and change into gaseous state at
relatively low temperature. The volatility of a substance depends upon the strength of intermolecular
attractive forces. Weaker the intermolecular attractive force more volatile will be the substance and vice
versa.
Since organic compounds have generally weak inter molecular forces due to their nonpolar nature that
is why organic compounds are volatile in nature.
Q10. The chemical properties of a homologous series are always the same?
Ana: The chemical properties of a homologous series are always the same due to the following reason:
Reason: The chemical properties of a homologous series depend on the functional group because it is
the functional group which takes an active part in a chemical reaction.
As all the members (homologues) of a homologous series have the same functional group that is why
chemical properties of a homologous series are always the same.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 28

LONG QUESTONS
Q1.List the different characteristics of organic compounds.
Ans: Characteristic properties of organic compounds:
Organic compounds have the following general properties:
i. Origin: The main source of organic compounds is plants and animals.
ii. Composition: Carbon is an essential component of all organic compounds. However, beside carbon
they also contain hydrogen as essential part. They may also contain some other elements like sulphur,
nitrogen, oxygen and halogen.
iii. Thermal instability: Many organic compounds are thermally unstable and decompose to simple
substances on heating. This property is of great commercial importance e.g. as in the cracking of
petroleum.
iv. Low melting points and boiling points: Organic compounds have generally low melting points and
boiling points due to weak intermolecular forces. They can be easily broken down and are generally
volatile in nature.
v. Bonding: Organic compounds are generally covalent in nature.
vi. Solubility: As most of the organic compounds are non-polar therefore, they are soluble in non-polar
solvent like benzene, acetone, and ether and less soluble or insoluble in polar solvents like water.
vii. Electrical conductivity: Most of the covalent compounds are non-polar therefore, poor conductors
of electricity in molten or solution form.
viii. In flammability: Most of the organic compounds are inflammable. They burn out to give carbon
dioxide, water vapours and energy.
ix. Reactivity: The reactions of organic compounds are much slower than the inorganic compounds.
x. Isomerism: The compounds having same molecular formula but different structures are called
isomers and this phenomenon is called isomerism. Isomerism is common in most organic compounds.
For example, butane has two isomers n-butane and iso-butane both have the molecular formula C4H10
but they have different structures.
b. Which of these is not an unsaturated molecule?
i. C6H6 ii. C6H6 iii. C8H18 iv. C3H6
C. Define destructive distillation of coal. Name the different types of products obtained by the
destructive distillation of coal.
Ans: Destructive distillation:
The heating of a compound in the absence of air is called destructive distillation.
Destructive distillation of coal:
The process in which coal is heated in the absence of air is called destructive distillation of coal.
Products of destructive distillation of coal:
During this process, the coal is converted into coal gas, coke and coal tar and ammmonical liquior,
which are the sources of other organic compounds.
Q2. What is catenation?
Ans: Catenation:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 29

The self-linking ability of carbon atoms to covalently bond with other carbon atom to form straight
chain, branched chain and rings is called catenation.
b. How does catenation contribution to the diversity of organic compound?
Ans: Catenation contribute to the diversity of organic compound by allowing carbon atoms to bond
together in many possible arrangement .Due to catenation variety of molecules with different structures
including chains and rings of many shapes and sizes are formed which have different properties.
Examples:

Q3. What information about a compound is provided by structural formula?

Ans: Structural formula:
Structural formula of a compound is the arrangement of different atoms of various elements around the
carbon atoms present in a molecule of a compound.
Importance:
A structural formula shows number and types of atoms present in a molecule and also shows the bonding
arrangement of the atoms.
In structural formula, all the bonds are shown with their exact number. Single bonds are represented by a
single line between the bonded atoms.
Example: Structural formula of butane C4H10,

b. How are structural formula used in organic chemistry?

Ans: structural formula have particular importance in the study of organic chemistry. They show the
arrangement of atoms in the molecules as far as which atoms are bonded to which and whether single,
double, or triple bonds are used.
For example, the molecular formula C4H10 does not tell which atoms are bonded to which other atoms
but structural formula shows all arrangement. For example:

Q4. (A). what do term saturated and unsaturated mean when applied to hydrocarbons?
Ans: Hydrocarbons:
The compounds of carbon and hydrogen are called hydrocarbons”.
Classification of hydrocarbons: Hydrocarbons are classified into two main groups:
i. Saturated hydrocarbons (alkanes)
ii. Unsaturated hydrocarbons (alkenes and alkynes)
i. Saturated hydrocarbons: “The hydrocarbons which contain all carbon-carbon single bonds are
called saturated hydrocarbons or alkanes”.
General formula: They have the general formula of CnH2n+2, where n is the number of carbon atoms.
Examples:
Methane (CH4), Ethane (C2H6), propane (C3H8) and butane (C4H10) etc are the examples of saturated
hydrocarbons.
ii. Unsaturated hydrocarbons: “The hydrocarbons containing at least one carbon-carbon double or
triple bond are called unsaturated hydrocarbons”. They are further classified to:
a. Alkenes: “The hydrocarbons which contain at least one carbon-carbon double bond are called
alkenes”.
General formula: They have the general formula of CnH2n, where n is the number of carbon atoms.
Example:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 30

Ethene (C2H4), propene (C3H6), Butene (C4H8) and pentene (C5H10) are the examples of alkanes.
b. Alkyne: The hydrocarbons which contain at least on carbon─carbon triple bonds are called
alkynes.”
General formula: They have the general formula of CnH2n-2, where n is the number of carbon atoms.
Examples: Ethyne (C2H2), propyne (C3H4), butyne (C4H6), and pentyne (C5H8) etc are the examples of
alkynes.
b. What other meanings do these term have in chemistry?
Ans: Saturated:
In chemistry term saturated also refer to chemical solutions. A solution which can’t dissolve more
solute is called saturated solution.
Unsaturated:
A solution which can dissolve further amount of solute to form a saturated solution is called
Unsaturated solution.
c. Classify alkenes, alkanes, alkynes, and aromatic hydrocarbons as either saturated or
unsaturated.
Ans: Alkanes: The hydrocarbons which contain all carbon-carbon single bonds are called saturated
hydrocarbons. As alkanes contain all C-C singles bonds so alkanes are saturated hydrocarbons.
Unsaturated hydrocarbons: The hydrocarbons containing at least one carbon-carbon double or triple
bond are called unsaturated hydrocarbons. Alkenes and alkynes contain double and triple bonds and
aromatic hydrocarbons contain alternate single and double bonds. So, alkenes, alkynes and aromatic
hydrocarbons are unsaturated.

Q5. Can you explain the term homologous series?

Ans: Homologous series :( Homo = same, logos = properties). “A serried of organic compounds having
same chemical properties but each member differs from the adjacent member by methylene group (-
CH2-) is called homologous series while each member of homologous series is called homologue”.
Properties of homologous series:
i. They have the same general formula.
ii. They have the same functional group.
iii. They have same chemical properties.
iv. Each member of homologous series differs from adjacent member by –CH2- group.
v. They have the same general methods of preparations.
Examples:
There are seven homologous series of the organic compounds they are hydrocarbons, alcohols,
carboxylic acids, carbonyl compounds (aldehydes and ketones), ethers, amines and alkyl halides.
b. How straight chain hydrocarbons are named.
Naming of alkanes (nomenclature): “The naming of alkanes under certain rules is called
nomenclature”.
Rules for naming alkanes (straight chain): Simple straight chain alkanes can be named by the
following rules:
i. Count the number of carbon atoms in the formula of alkanes.
ii. Give prefixes meth for 1, eth for 2, prop for 3, but for 4 carbon atoms respectively etc.
iii. Add suffix-ane to the corresponding prefix. Thus, the full name of simple straight chain alkane is
obtained.
Examples:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 31

Chemical
Number of Greek numerals
formula Full Name
C-atoms (Prefixes)
(CnH2n+2)

CH4 1 Meth- Methane

C2H5 2 Eth- Ethane

C3H8 3 Prop- Propane

C4H10 4 But- Butane

C5H12 5 Pent- Pentane

C3H14 6 Hex- Hexane

C7H16 7 Hept- Heptane

C8H18 8 Oct- Octane

C9H20 9 Non- Nonage

C10H22 10 Dec- Decane

C. name the straight chain alkane with the molecular formula C8H18.
Ans: As the number of carbon atom is eight and the prefix Greek numerals oct is used for 8. So, the
name of given compound C8H18 is octane.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 32

TOPIC WISE QUESTIONS

Q1.What is vital force theory? Why it was rejected?
Ans: Vital force theory:
According to this theory organic compounds cannot be prepared in laboratory. They are only prepared in
the bodies of living organisms under the influence of a supernatural force called vital force.
For example:
Urea (from urine), tartaric acid (from grapes), citric acid (from lemon) and sucrose (from cane sugar) are
organic compounds.
Rejection of vital force theory:
In 1828, a German chemist Friedrich Wohler prepared an organic compound (urea) in the laboratory by
heating ammonium connate and rejected the vital force theory.
Ammonium cynate is obtained by heating solid ammonium chloride with solid potassium cynate.
NH4CI(s) + KCNO(s) →NH4CNO(s) + KCI(s)
NH4CNO(s)→H2NCONH2 (urea)
Q2. Define organic compounds and organic chemistry?
Ans: Organic compounds:
“The compounds of carbon and hydrogen called hydrocarbons and their derivatives are called organic
compounds”.
Composition of organic compounds:
All organic compounds contain carbon and hydrogen as an essential ingredient beside these elements
they may also contain halogens, sulphur, oxygen, nitrogen.
Derivatives of hydrocarbon:
When hydrogen atom of hydrocarbon is replaced by an atom or group of atoms then the resulting
compound will be the derivate of that hydrocarbon.
For example:
If we remove one H from ethane C2H6 then ethyl group (C2H5) is obtained thus ethyl alcohol(C2H5OH),
ethyl chloride (C2H5CI), ethyl bromide (C2H5Br) are the examples of derivatives of ethane.
Organic chemistry:
“The branch of chemistry which deals with the study of hydrocarbons and their derivatives is called
organic chemistry”. For example in this branch we study about alkanes like methane, alcohols like
ethyl alcohol etc.
Q3. Define molecular, structural, condenced and dot and cross formula?
Ans: Molecular formula:
The formula which represents the actual number of atoms in one molecule of organic compound is
called the molecular formula.
Example:
The molecular formula of propane is C3H8, and butane isC4H10,
It shows that propane consists of three carbon and eight hydrogen atoms and
Structural formula:
The structural formula a compound is the arrangement of different atoms of various elements around
the carbon atoms present in a molecule of a compound.
Example:
Structural formula of butane is.

Condensed formula:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 33

The condensed formula of a molecule is the formula where the groups of atoms are shown in order as
they appear in the structural formula with no bonds or dashes.
Example:
Hexane has six carbon and fourteen hydrogen atoms with molecular formula of C6H14. The condensed
formula of hexane is CH3 (CH2)4CH3.
Dot and cross formula:
A structural formula in which electrons are shown as dots and cross between various atoms in one
molecule of a compound are called dot and cross formula.
Example:
In methane molecule, the four electrons of carbon is represented by dots (●) and cross (×) is used to
represent the electrons of four hydrogen atoms. The molecules of methane and of propane is shown
below.
Q4. Explain the classification of organic compound?
Ans: Classification of Organic compound: On the basis of structure of carbon chain, organic
compound are classified into the following two groups:
i. Open chain alkanes
ii. Cyclic alkanes
i. Open chain organic compound or aliphatic organic compound: “The type of organic compound
which consist of open chain of carbon atoms are called open chain or aliphatic organic compound”.
Open chain organic compound are further classified into two types which are given below:
a. Straight chain organic compound s: “The type of open chain organic compound which contain
straight chain of carbon in their molecules are called straight chain organic compound”.
A carbon atom in straight chain organic compound is not directly bonded to more than two carbon
atoms. They are commonly named as n-alkanes (normal-alkanes).
Examples:
Some examples of straight chain alkanes are given below:
CH3-CH2-CH2-CH3 (n-butane)
CH3-CH2-CH2-CH2- CH3 (n-pentane)
CH3-CH2-CH2-CH2- CH2-CH3 (n-hexane)
b. Branched chain organic compound: “The type of open chain organic compound which do not
contain straight chain of carbon in their molecules are called straight chain organic compound”.
At least one carbon atom in branched chain alkanes is directly bonded to more than two carbon atoms.
They are commonly named as iso-alkanes.
Examples:

ii. Cyclic alkanes: “The type of organic compound in which the carbon atoms are linked together to
form a close chain structure
Are called cyclic alkanes or cyclo-alkanes”.
These have the general formula similar to alkenes i.e. CnHn2
The closed chain alkanes are further divided into two groups. These are,
i. Homocyclic or Carbocyclic organic compound
ii. Heterocyclic organic compound
i. Homocyclic or Carbocyclic organic compound:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 34

Organic compounds which are in close chain structure are called Homocyclic compounds. The ring is
composed of only carbon atoms.
Homocyclicorganiccompound are further divided into two types.
a. Ali-cyclic organic compound
b. Aromatic organic compound
a.Ali-cyclic organic compound:
The cyclic organic compound which is composed of only carbon atom is called Ali-cyclic organic
compound.
These organic compounds have properties similar to open chain organic compound but differ in their
structure and formulae.
Example:

Aromatic organic compound:

The cyclic organic compound having alternate single and double bonds in its structure are known as
aromatic organic compounds.
Examples:

The important member of this class is benzene and the derivatives of benzene i.e. Naphthalene,
Anthracene.
ii. Heterocyclic organic compound:
The organic compound which contain one or more atoms other than carbon such as sulphur, oxygen or
nitrogen in the ring are called heterocyclic organic compound.
Example:
Examples are furan, thiophene and pyridine.

Q5. What are alkanes? Give examples.

Ans: Alkanes:
“The saturated hydrocarbons containing all carbon carbon single bonds are called alkanes or pyramids.
Reason of calling paraffin’s: Paraffin is a Latin word meaning “little affinity”. Since alkanes contain C-
C and C-H single bonds, therefore they have little affinity towards chemical reactions that is why they
are called paraffin’s.
Reason of calling saturated hydrocarbons: Since in alkanes each carbon atom is bonded with four
other atoms, therefore no further atom can be added to alkanes. Hence, they are called saturated
hydrocarbons.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 35

General formula: The general formula of alkanes is CnH2n+2 where n is the number of carbon atoms e.g.
if n=1 then the formula will be CH4 which is called methane. Similarly, if n=2 then the formula will be
C2H6 called ethane etc.

Example:
S. No. Name of alkane Chemical formula (CnH2n+2)

1 Methane CH4

2 Ethane C2H6

3 Propane C3H8

4 Butane C4H10

5 Pentane C5H12

Q7. Describe the sources of organic compound?

Ans: Sources of organic compounds:
Sources of organic compounds may be natural or they may be prepared synthetically.
Natural sources of organic compounds: Coal, petroleum and natural gas are then main sources of large
variety of organic compounds. They are called fossil fuels. Similarly, plants are also a source of organic
compounds.
Formation of fossil fuels:
Coal, petroleum and natural gas are called fossil fuels because they are formed from the decay of plants
and animals buried under ground. After a long period of time the plants and animals buried under
ground. After a long period of time the plants and animals were changed to fossil fuels.
The detail of natural sources is given below:
i. Coal: Coal is a brown black solid mass and a major source of organic compounds.
Formation of coal: coal is formed from the remain of plants. Under the chemical and bacterial action on
the remain of plants and trees, It is converted into peat. Peat under high temperature and pressure is
converted into coal.
Coal as a source of organic compound:
Coal is a rich source of organic compounds. These organic compounds are obtained by the process of
destructive distillation.
Destructive distillation of coal:
The process in which coal is heated in the absence of air is called destructive distillation of coal.
Products of destructive distillation of coal:
During this process, the coal is converted into coal gas, coke and coal tar and ammmonical liquior,
which are the sources of other organic compounds.
Uses: Coal is a major source of organic compounds. It is used as a solid fuel.
ii.Petroleum:
Petroleum is the combination of two Latin words pet means rock, and oleum means oil.
Petroleum is also an important source of organic compounds. It may be defined as follows:
“A dark brown coloured and unpleasing smelling liquid that consists of mixture of various
hydrocarbons, found in sedimentary rock of earth is called petroleum”.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 36

It is also called rock oil, crude oil and liquid gold.

Composition of petroleum: Petroleum consists of hydrocarbons majority of which are open and cyclic
alkanes and aromatic compounds.
Uses: After refining petroleum is used as a fuel in the form of petrol, diesel, kerosene etc. It is also used
for the production of useful products like synthetic rubber, plastics and explosives etc.
iii. Natural gas: It is also a natural source of organic compounds. It may be defined as:
“A flammable gaseous mixture consisting of low molecular hydrocarbons found naturally inside earth is
known as natural gas”. It is usually found together with petroleum.
Composition: Natural gas consists of low boiling point hydrocarbons. These hydrocarbons are 85%
methane and 15% ethane, propane and butane. It may also contain small amounts of hydrogen sulphide
(H2S), nitrogen (N2) and (CO2) which are often removed during refining process.
Uses: Natural gas is used as fuel for domestic as well as industrial purposes. It is also used as a fuel in
automobiles as compressed natural gas (CNG). It is also used for the preparation of carbon black and
also as a basic raw material in the preparation of fertilizers.
iv.Plants: Plants are the main source of organic compounds. These compounds are mainly protein,
carbohydrates, vitamins, fats and oils. these compounds are obtained from plants in the form of leaves,
stems, fruits, flowers, seed sand roots etc. these compounds are called Natural products.
v. Animals: Animals are also good source of organic compounds. Most organic compounds such as
protein, carbohydrates, vitamins, fats, etc are obtained from animals in form of milk, meat, butter and
egg etc
Synthetic sources: Organic compounds are also prepared in laboratory and industries. In earlier times it
was thought that organic compounds cannot be prepared in laboratory (Vital force theory) but after the
synthesis of urea (H2NCOH2) from inorganic compound this theory was rejected and a large number of
organic compounds were prepared in the laboratory and industries.
Q8. What is functional group? Explain with examples.
Ans: Functional group:
A functional group is an atom or group of atoms attached with R that is responsible for the specific
properties of an organic compound.
Explanation: A functional group is the active part of an organic compound. Most of the organic
compounds consist of two parts i.e.
i. The hydrocarbon part which is an alkyl group/
ii. The functional group part.
For example:
In methanol (CH3-OH),-CH3 is the alkyl group (R) while –OH) is the functional group part.
Classification of functional groups: Functional groups can be classified into following types:
i. Functional groups containing Carbon, Hydrogen and Oxygen:
Organic compounds containing carbon, hydrogen and oxygen as a functional groups are alcohols (-OH)
Carbonyl compound which may be aldehydes or ketones (C=O), ethers (-O-) and carboxylic acids (-
COOH) and the derivatives such as esters, acid halides and acid amides.
Examples:
Functional General Name of the Examples Name of
group formula classes compound

-OH R-OH Alcohols CH3-OH Methyl alcohol

-CHO R/H- CHO Aldehydes CH3-CHO Ethanal

 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 37

-CO- R-CO-R Ketones CH3-CO-CH3 Propanone

-COOH R-COOH Carboxylic acids CH3-COOH Ethanoic acid

-O-R R-O-R Ether CH3-O-CH3 Di methyl ether

ii. Functional groups containing C, H and N: functional groups containing carbon hydrogen and
nitrogen are called amines. Functional group of amines is -NH2. The general formula is R-NH2.
For examples methyl-amine (CH3-NH2)
iii. Functional groups containing C,H and X:
Functional groups containing carbon hydrogen and halogens are called alkyl halides. Functional group
of alkyl halides is halogens represented by ‘X’. The general formula is R-X. X may be F, Cl, Br, or I for
examples methyl-chloride (CH3-Cl)
CHEMISTRY
Class 10th (KPK)

NAME: __________________________

F.NAME: _________________________

CLASS:___________ SECTION: ________

ROLL #: _____ SUBJECT: ____________

ADDRESS: ___________________________________

__________________________________________

SCHOOL: _____________________________________

https://web.facebook.com/TehkalsDotCom/

https://tehkals.com/
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 38

Unit 12
HYDROCARBONS
Short Questions:
Q1. How would you test that alkenes undergoes an addition reaction?
Ans: Addition reaction of alkenes: alkenes are unsaturated hydrocarbons and can be converted to
saturated hydrocarbon. Addition reaction is characteristics properties of alkenes. One of the addition re
action is addition of halogens (Halogenation).
Halogenation of alkene:
When bromine is added to ethene in the presence of an inert solvent like carbon tetra chloride (CCl4),
the double bond of it is converted into single bond. The red colour of bromine is disappear and
produces 1, 2-dibromoethane.

Q2. Which one is more reactive between alkane and alkene? Explain.
Ans: Alkenes are more reactive than the corresponding alkanes due to the following reason:
Reason: Alkenes contain C-C double bonds and double bonds are weaker and can easily be broken.
Therefore, alkenes are more reactive. On the other hand alkanes contain all C.C single bonds which are
stronger and cannot be easily broken that is why alkenes are more reactive than the corresponding
alkanes.
For example, ethane does not react with bromine solution while ethane reacts easily with bromine
solution decolourizing its red colour.
Q3. Justify alkenes and alkynes as unsaturated hydrocarbons.
Ans: Unsaturated hydrocarbons:
The hydrocarbons containing at least one carbon-carbon double or triple bond are called unsaturated
hydrocarbons. Alkenes contain C=C double and alkynes contains C≡C triple bonds. Therefore, alkenes
and alkynes are termed as unsaturated hydrocarbons.
Q4. Why alkane is inert in nature?
Ans: Alkanes are chemically inert in nature due to the following reason:
Reason: Alkanes are chemically inert in nature because they contain carbon-carbon single bonds. The
single bonds are very strong and stable and high energy is required to break them; therefore, alkanes
are chemically inert as compared to alkynes and alkenes because they contain double or triple bonds
which can easily be broken.
Q5. What happened when alkyl halide is reduced?
Ans: Reduction of alkyl halides:
Reduction means addition of hydrogen. Alkyl halides on reaction with nascent hydrogen in the
presence of Zinc dust and HCl form the corresponding alkane’s i.e. methyl halide will form methane,
ethyl halide will form ethane etc.
General reaction of alkyl halide and nascent hydrogen to form alkane is:
R─X + 2[H] → R─H + HX
Methyl iodide gives methane and hydrogen iodide HI.
CH3─I+ 2[H] → CH3─H+ HI
Similarly, ethyl bromide gives ethane and hydrogen bromide HBr.
CH3─ CH2 ─Br + 2[H] → CH3─ CH2 ─H+ HBr
Q6. Can you predict the products if KMnO4 solution reacts with alkene?
Ans: Oxidation of alkanes by KMnO4 (Baeyer’s test):
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 39

Alkenes react with cold dilute potassium permanganate solution to form glycol. Glycols are the
alcohols containing two hydroxyl groups (-OH) on two adjacent carbon atoms.
The reaction of potassium permanganate with ethane is given below:
3CH2=CH2+2KMnO4+4H2O → 3CH2-CH2+2MnO2+2KOH
│ │
OH OH
(Ethylene glycol).
Q7. Why colour of bromine water discharges on addition to ethene?
Ans: when bromine water having red brown colour is added to ethene in the presence of inert solvent
like carbon tetra chloride, its colour is discharged. Because during this reaction bromine water reacts
with ethene in carbon tetra chloride to form ethylene bromide which is colourless compound.

Q8. Compare the reactivity of alkane and alkene.

Ans: Alkenes are more reactive than the corresponding alkanes due to the following reason:
Reason: Alkenes contain C-C double bonds and double bonds are weaker and can easily be broken.
Therefore, alkenes are more reactive. On the other hand, alkanes contain all C.C single bonds which
are stronger and cannot be easily broken that is why alkenes are more reactive than the corresponding
alkanes.
For example, ethane does not react with bromine solution while ethane reacts easily with bromine
solution decolourizing its red colour.
Q9. Why addition reactions take place in ethane and ethyne but not in ethane?
Ans: Addition reactions take place in ethane and ethyne but not in ethane due to the following reason.
Reason: Carbon atom has four electrons in its valance shell and it can directly for bond with maximum
of four atoms.
Ethane and ethyne are unsaturated hydrocarbons containing C-C double and triple bonds respectively.
Therefore, the two carbon atoms of ethane and ethyne are directly bonded with less than 4 other atoms.
Therefore, no further atoms can be added to it i.e. addition reaction does not occur only substitution
reaction occur in ethane by the replacement of H-atoms.
Q10. Write equation for the preparation of ethene from ethyl alcohol and ethyl chloride.
Ans: Ethene from ethyl alcohol:

Ethene from ethyl chloride:

 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 40

LONG QUESTIONS
Q1. (i). write down the equations for the preparation of alkanes, alkenes and alkynes.
Ans: Preparation of alkanes:
1. Hydrogenation of alkenes:
Alkanes can be prepared by the hydrogenation of alkenes. During this reaction alkenes are
hydrogenated in the presence of Nickel (Ni) catalyst at 250- 300 0C temperature.
H2C═ CH2 + H─H →H3C ─CH3
Ethene Ethane
2. Hydrogenation of alkynes:
Alkynes are hydrogenated to alkenes in the presence of Nickel (Ni) catalyst at 250- 300 0C temperature
in the first step and in the second step, alkene is further hydrogenated and converted into alkanes.
HC ≡ CH + H─H → H2C═ CH2
H2C═ CH2 + H─H →H3C ─CH3
3. Reduction of alkyl halides:Alkyl halides on reaction with nascent hydrogen in the presence of Zinc
dust and HCl form the corresponding alkanes i.e. methyl halide will form methane, ethyl halide will
form ethane etc.
General reaction of alkyl halide and nascent hydrogen to form alkane is:
R─X + 2[H] → R─H + HX
Methyl iodide gives methane and hydrogen iodide HI.
CH3─I+ 2[H] → CH3─H+ HI
Preparation of alkenes:
1. Dehydrogenation of alcohols:
In this reaction water molecule is removed from alcohol and double bond is formed. This reaction is
carried out in the presence of concentrated Sulphuric acid at 180oC.

2. Dehydrohalogenation of alkyl halides:

When an alkyl halide is heated with alcoholic solution of potassium hydroxide (KOH) a molecule of
hydrogen halide is removed and an alkene is formed. During this reaction hydrogen is removed from
one carbon and halogen is removed from the other adjacent carbon atoms.
For example, ethyl chloride on dehydrohalogenation gives ethene and hydrogen chloride (HCl).

Preparation of alkynes:
1. Dehalogenation of adjacent Dihalides:
The organic compound in which dihalides are attached to the adjacent carbon atoms are called vicinal
dihalides.
The reaction occurs in two steps.
Step 1.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 41

Vicinal dihalides such as 1, 2-dibromoethanethane is heated with alcoholic potassium hydroxide

solution, removal of hydrogen takes place from one carbon and bromine from other. It results in
double bond and produces bromoethane and hydrogen bromide.

Step 2. In the next step another molecule of hydrogen bromide is removed and the double bond is
converted into triple bond.

2. Dehalogenation of Tetra halide:

The compound contain four halogens atoms at two adjacent carbon atoms are called tetra halides.
When alkyl tetra halides for example 1, 1, 2,2-tetrabromoethane is treated with reactive metal like zinc
(Zn) dust. It eliminates two bromine and form triple bond, producing ethyne and zinc bromide (ZnBr2).

Q1.(ii) Draw the molecular, dot, and cross, condensed and structural formula of each of the
following.
Propene, Butyne, Pentane, Heptyne, butane.

s.no Molecular Condensed formula Dot and Structural

formula cross formula
formula

Propene C3H6 CH2CHCH3

Butyne C4H6 CH3CH2CCH

Pentane C5H12 CH3CH2CH2CH2CH3

Heptyne C7H12 CH3CH2CH2CH2CH2C≡CH

Butane C4H10 CH3CH2CH2CH3

Q2. (i). the general formula of alkanes is CnH2n+2. Determine the general formula of cycloalkane?
Ans: Cycloalnaes: The alkanes in which carbon atoms are arranged in a ringorcyclic structure is called
cycloalkanes.The general formula of Cycloalnaes: The general formula of cycloalkanes is CnH2n.
Cycloalkanes have less than two hydrogen atom than in corresponding straight chain alkanes.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 42

(ii). write a balanced equation for the complete combustion of each of the following.
a. Methane b. Ethane c. Ethyne
a.Combustion of Alkanes: Alkanes burn completely in the presence of excess of air (oxygen) to
produce a lot of heat, carbon dioxide and water. The reaction is highly exothermic and thus alkanes is
used as a fuel.
CH4 + 2O2 → CO2 + 2H2O + heat
Combustion of Alkenes: On complete combustion, alkenes produce carbon dioxide and water with
the release of high amount of energy.
C2H4 + 3O2 → 2CO2 + 2H2O + heat
C.Combustion of Alkynes:On complete combustion, alkynes produce carbon dioxide and water with
the release of high amount of energy,
2C2H2 + 5O2 → 4CO2 + 2H2O + heat.
(iii). Explain briefly that why ethyne (a) undergoes addition rection in two steps?
Answer: In addition reaction of ethyne first triple bond is converted into double bond and then double
bond is converted into single bond. That is the reason ethyne undergoes addition rection in two step.se
Example: hydrogenation of ethyne:
Step 1.HC ≡ CH + H─H → H2C═ CH2 Step 2. H2C═ CH2 + H─H →H3C ─CH3.
Q3. (i). Give an example reaction of that would yield the following products. Name the organic
reactants and products in each reaction.
Ans: a). Alkanes:
Hydrogenation of alkenes: alkanes can be prepared by the hydrogenation of alkenes. During this
reaction alkenes are hydrogenated in the presence of Nickel (Ni) catalyst at 250- 300 0C temperature.
H2C═ CH2 + H─H →H3C ─CH3
Ethene Ethane
b). Mon halogenated alkanes: Alkanes react with halogens in the presence of UV light and produce
alkyl halide and hydrogen halide.
H3C ─H + Cl ─ Cl → H3C─Cl + HCl
Methane methyl chloride c). Di
halogenated alkanes:
Cl─CH2─H + Cl ─ Cl → Cl─CH2─Cl + H─Cl
methyl chloride Dichloromethane
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 43

d). Tetra halogenated alkanes:

Cl3C─H + Cl ─ Cl → CCl4 + H─Cl
Dichloromethane tetrachloromethane
(ii). (a). Alkanes are unsaturated hydrocarbons. Explain the word unsaturated.
Ans: The word unsaturated means the organic compound having at least one carbon-carbon double or
triple bond. The unsaturated hydrocarbons having hydrogen less than that of saturated hydrocarbons.
Therefore, unsaturated hydrocarbons can easily undergo addition reaction.
(b). Describe the bonding between two carbon atoms in ethene.
Ans: bonding in ethene: Ethene is an unsaturated hydrocarbon containing two carbon atoms that are
bonded to each other. With each carbon atom also bonded two hydrogen atoms.

(c). which functional group is present in alkene?

Ans: In alkene C═C double bond functional group is present.
(d). Describe a simple chemical test to determine whether an unknown hydrocarbon is
unsaturated. Describe the result if the test is positive.
Ans: The two widely used tests for determining the unsaturation in compound is bromine water test
and Baeyer’s test.
1. Bromine water test: add a few drops of bromine water to the substance under test and shake. If
there are any carbon═ carbon double bonds then the red coloured bromine water will become
colourless. The red colour of bromine is disappearing. During this test bromine water reacts with
ethene to form ethylene bromide which is colourless compound.

2. Baeyer’s test:
This test is used for determining the presence of double bond in compounds. Alkenes is reacted with
acidified aqueous solution of potassium permanganate (KMnO4) and form ethylene glycol (1, 2-
ethanediol). During this reaction purple colour of KMnO4.

3H2C ═CH2 + 2KMnO4 + 4H2O → 3H2C─ CH2 + 2MnO2 + 2KOH

│ │
b OH OH
Q4. Using structural formula, give balanced equations for the following reactions.
(a). Ethene with Chlorine:
Chlorine readily react with ethene in the presence of inert solvent carbon tetra chloride to form
dichloro ethane.

(b). Ethene with hydrogen, name the catalyst used. Which industrial process uses a similar
reaction?
Hydrogenation of ethene:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 44

When hydrogen (H2) is added to ethene, the double bond is converted into single bond and produces
ethane. The reaction occur in the presence of nickel as a catalyst at 250-3000C.

(c). Ethene with hydrogen bromide:

The hydrogen (HBr) react with reacts with ethene and produces Ethyl bromide (Bromoethane).

(d). Ethene with KMnO4:

Alkenes react with acidified aqueous solution of potassium permanganate (KMnO4) to form glycol.
Glycol are alcohols which contain two hydroxyl groups (-OH) on two adjacent carbons.
3H2C ═CH2 + 2KMnO4 + 4H2O → 3H2C─ CH2 + 2MnO2 + 2KOH
│ │
b OH OH
Q5. Illustrate the following accordingly has been instructed.
(A). Alkane from Alkyl Halide
Reduction of alkyl halides: Alkyl halides on reaction with nascent hydrogen in the presence of Zinc
dust and HCl form the corresponding alkanes i.e. methyl halide will form methane, ethyl halide will
form ethane etc. General reaction of alkyl halide and nascent hydrogen to form alkane is:R─X + 2[H]
→ R─H + HX Methyl iodide gives methane and hydrogen iodide HI.CH3─I+ 2[H] →
CH3─H+ HI(b). Bromoethane from Ethene: When bromine is added to ethene in the presence of an
inert solvent like carbon tetra chloride (CCl4), the double bond of it is converted into single bond. The
red colour of bromine is disappearing and produces 1, 2-dibromoethane.

(c) Ethylene glycol (1, 2-ethanediol) from Ethene:

Alkenes react with acidified aqueous solution of potassium permanganate (KMnO4) to form glycol.
Glycol are alcohols which contain two hydroxyl groups (-OH) on two adjacent carbons.
3H2C ═CH2 + 2KMnO4 + 4H2O → 3H2C─ CH2 + 2MnO2 + 2KOH
│ │
b OH OH
(d). Oxalic acid from Acetylene:
The reaction of acetylene with potassium permanganate gives carboxylic acid and carbon dioxide on
breaking the molecule of carbon─carbon triple bond.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 45

TOPIC WISE QUESTIONS

Q2. What are addition reaction?
Ans: Addition reaction: The reaction in which two or more substances react to form only one
substance are called addition reaction.
With regard to organic compounds addition reactions can be defined as:
“the reaction in which molecules like H2, Cl2,HCl etc. are added to alkene and alkynesis called
addition reaction. Addition reaction occur only in unsaturated hydrocarbons. During addition reaction
unsaturated hydrocarbons are changed to saturated hydrocarbons

Q3. Write down the physical properties of Alkanes;

Ans: Physical properties:
i. Physical state: The first four members (methane, ethane, propane, butane) of alkane series are gases.
Next thirteen members (from C5H12 to C17H36) are colourless liquids and higher members of the series
are solids.
ii. Solubility: Since alkanes are non-polar therefore, they are soluble in non-polar solvents like
benzene, acetone, ether etc. However they are insoluble on polar solvents like water.
iii. Meting points and boiling points: The melting points and boiling points of alkanes increases with
the increase in molecular masses because generally higher molecular masses alkanes have stronger
intermolecular forces.
iv. Density: the density of alkanes increases regularly with increase in molecular mass.
V. viscous: Alkanes become more viscous as their molecular sizes increase.
vi. Flammable: Alkanes are flammable. With the increase of atomic mass the percentage of carbon in
alkanes molecules also increases. As a result, alkanes become less flammable.

Q4. Give important chemical reactions of alkanes.

Ans: Chemical properties: As carbon atoms of alkanes are directly bonded with 4 other atoms
therefore, only Substitution reaction reactions can occur in alkanes. Alkanes are chemically inert at
room temperature due to all C-C and C-H single bonds presents in them. However at higher
temperature, absorption of light etc the following reactions take place in them.
i. Halogenation: The substitution of hydrogen of an alkane by halogen is called halogenations.
Example: For example chlorine reacts with methane in the presence of diffused sunlight to form
chloro-methane (methyl chloride).
H3C ─H + Cl ─ Cl → H3C─Cl + HCl
Methane methyl chloride
This reaction does not stop here. The remaining three hydrogen atoms are also replaced by chlorine
atoms to form di, tri and tetra chloro-methane respectively
Cl─CH2─H + Cl ─ Cl → Cl─CH2─Cl + H─Cl
methyl chloride Dichloromethane
Cl─CH2─Cl + Cl─Cl → Cl3CH+ HCl
Dichloromethane Chloroform (tri-Chloromethane)
Cl3CH + Cl─Cl → CCl4
Chloroform Carbon tetrachloride
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 46

ii. Combustion: Alkanes react with oxygen or air at higher temperature to form carbon dioxide, water
vapours with evolution of large amount of heat.
Examples:
CH41g+O21g→ CO21g+H2Og+Heat
2C2H +7021g 4CO21g+6HOg+ Heat
In limited supply of oxygen, incomplete combustion of alkanes takes place and produce carbon
monoxide, water and carbon.
3CH41g+ 4O21g→ 2CO+ 6H2O + C

Q5. What is alkene? How it can be named?

Ans: Alkenes:
The unsaturated hydrocarbons containing at least one C-C double bond are called alkenes”.
General Formula: They have the general formula of CnH2n
In alkenes all the carbon atoms are not bonded with 4 other atoms i.e. at least two carbon atoms are
bonded with 3 other atoms. Addition reaction occur in alkenes.
Examples:
i. Methene (C2H4)4
ii. Propene (C3H6)
iii. Butene (C4H8)
iv. Pentene C5H10
Rules for naming alkenes:
The IUPAC rules for alkenes are as follow.
1. Select the longest continuous chain containing double bond (C═C) as the parent chain.
2. The parent name is derived from the named of the identical alkanes, in which the last –ane of
alkanes is replaced –ene.
3. Number the chain so as to include both carbon atoms of the double bond. Numbering begins from
the end which is nearer to the double bond.
4. The position of double is shown by numbering the alkene, so that minimum number is assigned to
the double bond
5. Designate the location of the double bond by using the number of the first atom of the double bond
as a prefix.
6. Indicate the location of the branches by numbers of the carbon atoms to which they are attached.

Q6. Write down physical and chemical properties of Alkenes.

Ans: Physical properties of alkenes:
i. Physical state: The first three members of alkene (ethene, propene, butene) are gases. Other
members are liquids and higher are solids
ii. Solubility: alkenes are non-polar therefore, they are soluble in non-polar solvents like benzene,
acetone, ether etc. However they are insoluble on polar solvents like water.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 47

iii. Meting points and boiling points: The melting points and boiling points of alkenes increases with
the increase in molecular masses because generally higher molecular masses alkenes have stronger
intermolecular forces.

Chemical properties Alkenes:

Because of the unsaturated nature of alkenes, they easily undergoes addition reaction and in this way,
they are converted into saturated compounds.
Important reaction of alkenes: Important reaction of alkenes include halogenation, addition of
hydrogen halides, oxidation by KMnO4, and hydrogenation. Theses reaction has already been discuss
in exercise.
Q7. Define alkynes. Give the rules for naming of alkynes.
Ans: Alkynes:”
The hydrocarbons which contain at least on carbon─carbon which contain at least on carbon- carbon
triple bonds are called alkynes.”
General formula: They have the general formula of CnH2n-2, where n is the number of carbon atoms.
Examples: Ethyne (C2H2), propyne (C3H4), butyne (C4H6), and pentyne (C5H8) etc are the examples of
alkynes.
Rules for naming alkenes:
The IUPAC rules for alkenes are as follow.
1. Select the longest continuous chain containing carbon- carbon triple bond (C ≡ C) as the parent
chain.
2. The parent name is derived from the named of the identical alkanes, in which the last –ane of
alkanes is replaced –yne.
3. Number the chain so as to include both carbon atoms of the triple bond. Numbering begins from the
end which is nearer to the triple bond.
4. The position of triple bond is shown by numbering the alkyne, so that minimum number is assigned
to the triple bond
5. Designate the location of the double bond by using the number of the first atom of the triple bond as
a prefix.
6. Indicate the location of the branches by numbers of the carbon atoms to which they are attached.

Q8. Write down physical and chemical properties of Alkynes.

Ans: Physical properties of alkynes:
i. Physical state: The first three members of alkyne (ethyne, propyne, butyne) are gases. Other
members are liquids and higher are solids
ii. Solubility: alkynes are non-polar therefore, they are soluble in non-polar solvents like benzene,
acetone, ether etc. However they are insoluble on polar solvents like water.
iii. Meting points and boiling points: The melting points and boiling points and density of alkynes
increases with the increase in molecular masses because generally higher molecular masses alkenes
have stronger intermolecular forces.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 48

iv.Combustion: on complete combustion, they produce carbon dioxide and water with the release of
high amount of energy,.
Chemical properties Alkynes:
Because of the unsaturated nature of alkynes, they easily undergoes addition reaction and in this way,
they are converted into saturated compounds.

Important reaction of alkenes:

1. Halogenation: Alkynes react with halogens such as chlorine and bromine in the presence catalyst
phosphorus trichloride (PCl3). The addition of halogens take place in two steps.
Step 1. In the first step a halogen molecule, i.e. chlorine (Cl2) or bromine (Br2) is added to triple bond.
Triple bond is converted into double bond and forms 1, 2-dichloroethene.

Step 2. In the second step another halogen molecule, i.e. chlorine (Cl2) or bromine (Br2) is added to
double bond. thw double bond is converted into single bond and forms 1,1,2,2-tetra chloro ethene.

2. Oxidation with KMnO4:

The oxidation of ethyne with potassium permanganate givs carboxylic acid and carbon dioxide on
breaking the molecule at carbon – carbon triple bond.
CHEMISTRY
Class 10th (KPK)

NAME: __________________________

F.NAME: _________________________

CLASS:___________ SECTION: ________

ROLL #: _____ SUBJECT: ____________

ADDRESS: ___________________________________

__________________________________________

SCHOOL: _____________________________________

https://web.facebook.com/TehkalsDotCom/

https://tehkals.com/
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 49

UNIT 13
BIOCHEMISTRY
Q1. Differentiate between glucose and fructose?
Ans: Difference between glucose and fructose:
Glucose and fructose are hexoses having same molecular formula C6H12O6. The main difference
between these two compounds is that glucose is pentahydroxy aldehyde having aldehydic functional
group, while fructose is pentahydroxy ketone having ketonic functional group.

Q2. Write down four uses of lipidsAns: i. Source of energy:

Lipids are good source of energy. One gram of lipids contains approximately twice more energy than a
gram of carbohydrates and protein.
Ii. As a part of protoplasm:
lipids are an important part of cell-protoplasm and plasma membrane.
iii. Act as a solvent:
lipids act as a solvent for some vitamin like A, D and E.
iv. Thermal insulator:
In mammals, a layer of fats is present under the skin. This layer acts as a thermal insulator. They
insulate the body from excessive heat or cold.
Q3. How do you differentiate between simple and complex lipids?
Ans: Simple Lipids:
The type of lipids which produce fatty acids and alcohol upon hydrolysis are called simple lipids. They
are also known as triglycerides.
Example: Fats, oils and waxes.
Complex Lipids:
The types of lipids which produce fatty acids, alcohols and some other substance upon hydrolysis are
known as complex lipids.
Example: phospholipids, Glycolipids, Sullpholipids
Q4. What is meant by denaturing of protein?
Ans: Denaturing of protein:The process in which protein lose their natural structure by heat or some
chemical substance is called\denaturing of protein.Due to denaturing the function of protein is
disturbed and they cannot perform their normal function.
Example: When egg is heated its protein (albumin) becomes hard thus denaturing of its protein
occurs.
Q5. How would you classify vitamins?
Ans:Classification of vitamins:
There are two types of vitamins.
i. Fats soluble vitamins ii. Water soluble vitamins
i.Fats Soluble Vitamins:
Vitamins which dissolve in fats are called fat soluble vitamins. These vitamins are a, D, E and K.
ii. Water Soluble Vitamins:
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 50

Vitamins which dissolve in water are called water soluble vitamins. These vitamins are B-complex and
Vitamin c. Vitamin B–complex include eight vitamins i.e. B1, B2, B3, B5, B6, Boltin, Folic acid and
B12.
Q6. Vitamin are vital for us?
Ans:Vitamins are vital for us because it plays an important role in the healthy development and growth
of our body. Our body needs a small amount of vitamins and minerals every day to remain healthy,
function properly and prevent in future from health problems. It also play important roles in bodily
function such as metabolism, immunity and digestion.
Q7.Write down the of sucrose hydrolysis
Ans: Hydrolysis of sucrose: On
hydrolysis sucrose produce one unit of Glucose and one unit of Fructose.
C12H22O11 + H2O → C6H12O6 + C6H12O6
Sucrose + H2O → Glucose + Fructose
Q8. Draw the general formula of amino acid. Identify the different parts and functional groups
present in it.
Ans: General formula of amino acid:Amino acid is an organic compound having central carbon
atom called alpha carbon, which is attached to basic amino group (NH2), acidic carboxyl group
(COOH), a side chain alkyl group (R) and hydrogen atom.

Q9. Briefly describe the sources and deficiency symptoms of Vitamin A.

Ans: Vitamin A.
Vitamin A is fat soluble which is important for growth, vision and immune system.
Sources:
Vitamin A is found in milk, butter, fish oils, eggs, fresh green vegetables and fruits.
Deficiency Symptoms: Deficiency of Vitamin A cause night blindness, dry skin, burning and irritation
of eyes.
Q10. Identify the different sources of proteins? Also, list the four uses of protein?
Ans: Sources of proteins: There are two main sources of protein animal sources and plant sources.
i. Animal Sources of Protein:
Animal sources of proteins are fish, meat, eggs, milk cheese etc.
ii. Plant Sources of Proteins:
pulses and beans are the plant sources of proteicarn and are used as a food source.
Important function of protein: Some important function of protein are given below.
I. as Oxygen carrier: Haemoglobin is a protein which carries oxygen to all cells of body.
ii. Body structure: Skin, nail, hair, hoofs, horns and feather are composed of proteins.
iii. Growth: Proteins are essential for the physical and mental growth especially in children.
iv. Enzymatic action: Enzymes are proteins, which are produced by the cells of living organisms.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 51

Enzymes catalyze the biochemical reactions going on in our bodies.

v. As Body regulators: Hormones and enzymes are the chemical regulators of the body.
vi. Body Defense System: The antibodies that help us to fight against diseases are large proteins
molecules
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 52

LONG QUESTIONS
Q1. What function do carbohydrates perform in living organisms?
Ans: Function of carbohydrates:1. Source of energy:
Carbohydrates are used by our body as a rich source of energy.
2. Source of food:
Carbohydrates are used as a source of food. For example, many vegetables fruits and cereals contain
carbohydrates. It is also used as a common sweetener for food.
3. Structural material:
Carbohydrates serves as a structural material in living organism. For example, plant cell wall is made
up of cellulose similarly exoskeleton of insects is made up of chitin.
4. Energy reservoir:
Glucose is stored in animal muscles and liver cell in the form of glycogen. It serves as a long term
energy reservoir in the body, converted back into glucose when needed. Plants store excess energy in
the form of starch.
5. Medicinal Uses: Constipation and diarrhea are mainly controlled bythe use of carbohydrates fibers.
Q2. (a). Distinguish between monosaccharaides, disaccharides and polysaccharides and also give
example of each one.
Ans: Carbohydrates:
Definition: “Polyhydroxy ketones or polyhydroxy aldehydes are called carbohydrates”.
Polyhdroxy means having many hydroxyl groups.
Common name: Carbohydrates are commonly known as sugars.
Composition: Carbohydrates are poly functional (alcohol+aldehydes or ketones) organic compounds
which mainly consist of carbon, hydrogen and oxygen some time along with nitrogen (chitin) or
sulphur (keratin sulphate).
Classification of carbohydrates: Carbohydrates are classified into the following three groups:
1. Monosaccharides 2. Oligosaccharides 3. Polysaccharides
Their detail is given below:
1. Monosaccharides:
Definition: “The simplest carbohydrates which cannot be further hydrolyzed into smaller units are
called monosaccharides”.
General formula: They have the general formula of Cn (H2O) n where n=3, 4, 5 and so on.
Composition: Monosaccharides are either aldoses having aldehydic functional group (for example
glucose) or ketoses having ketonic functional group for examples glucose) or ketoses having ketonic
functional group for example fructose.
These may be trioses (C3H12O6), tetroses (C4H8O4), pentoses (C5H10O5) and hexoses (C6H12O6).
General properties of monosaccharides: Some general properties of monosaccharides are:
i. Solubility: They are soluble in water.
ii. Physical state: They are crystalline solid at room temperature.
iii. Taste: They have sweet taste.
iv. Colour: They are colourless.
v. hydrolysis: They cannot be hydrolyzed further.
Examples: Some examples of carbohydrates along with their structures are given below:
In straight forms these structures can be written as following
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 53

2. Oligosaccharides: “Carbohydrates containing two to nine monosaccharide units are called

oligosaccharides.” OR
“The carbohydrates which yield two to nine monosaccharide units on hydrolysis in the presence of an
acid or enzyme are called oligosaccharides.”
Formation: They are formed when two to nine monosaccharide molecules combine with each other
by the loss of water molecules. These molecules are bonded with each other through glycosidic
linkage.
Types: Oligosaccharides have many types but two of them are described below:
a. Disaccharides: “Those oligosaccharides which consist of two monosaccharide units are called
disaccharides.”
Examples:
Disaccharides Monosaccharides
Maltose → Glucose+Glucose
Lactose → Glucose+Galactose
Sucrose → Glucose+Fructose
b. Trisaccharides: “Those oligosaccharides which consist of three monosaccharide units are called
trisaccharides.”
Examples: Reffinose, kestose and maltotriose (C18H32O16) etc.
General properties of oligosaccharides: Some general properties of oligosaccharides are:
i. Solubility: They are soluble in water.
ii. Physical state: They are crystalline solids.
iii. Taste: They are sweet taste.
iv. Colour: They are colourless.
v. Hydrolysis: They give two to nine monosaccharide units on hydrolysis.
3. Polysaccharides: “The biopolymers of monosaccharides which consist of 100 or more
monosaccharide units joined together through glycosidic linkage are called polysaccharides.”
Polysaccharides have high molecular weight and they hydrolyzed to give many molecules of
monosaccharides e.g.
General properties of polysaccharides:
i. Physical state: They are amorphous solids.
ii. Taste: They are tasteless and are called non-sugars.
iii. Solubility: They are insoluble in water.
iv. Hydrolysis: They give many molecules of monosaccharides on hydrolysis.
Examples: Cellulose, starch, dextrin and glycogen etc. are the examples of polysaccharides.
Function: Polysaccharides perform two main functions in animals and plants.
i. They are used as energy storage of cell.
ii. They are used as structural unit of cell
2. B. How carbohydrates are important to living organisms?
Ans: Importance of Carbohydrates: Carbohydrates are very important to living organism because
they perform very important function in living organism such as,
1. Source of energy:
Carbohydrates are used by our body as a rich source of energy.
2. Source of food:
Carbohydrates are used as a source of food. For example many vegetables fruits and cereals contain
carbohydrates. It is also used as a common sweetener for food.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 54

3. Structural material:
Carbohydrates serves as a structural material in living organism. Forexample plant cell wall is made up
of cellulose similarly exoskeleton of insects is made up of chitin.
4.
Energy reservoir:
Glucose is stored in animal muscles and liver cell in the form of glycogen. It serves as a long term
energy reservoir in the body, converted back into glucose when needed. Plants store excess energy in
the form of starch.
5. Medicinal Uses:
Constipation and diarrhea are mainly by the use of carbohydrates fibers.
Q3. a. How are proteins important to living organism?
Ans: Importance of proteins: Proteins are very important to living organisms because it performs
many important function in body. Some important function of protein are given below.
i. As Oxygen carrier: Haemoglobin is a protein which carries oxygen to all cells of body.
ii. Body structure: Skin, nail, hair, hoofs, horns and feather are composed of proteins.
iii. Growth: Proteins are essential for the physical and mental growth especially in children.
iv. Enzymatic action: Enzymes are proteins, which are produced by the cells of living organisms.
Enzymes catalyze the biochemical reactions going on in our bodies.
v. As Body regulators: Hormones and enzymes are the chemical regulators of the body.
vi. Body Defence System: The antibodies that help us to fight against diseases are large proteins
molecules.
3. b. Explain the nature of bonding in protein?
Ans: Nature of bonding in Protein:
In protein three types of bonding may occur.
1. Peptide Bonding 2. Hydrogen bonding 3. Disulphide bridges
1. Peptide Bonding: The bonding between carbonyl group (-C=O) and NH group are called peptide
bonding. Amino acid are linked together through peptide bonding to form proteins.

2. Hydrogen bonding:
The hydrogen bonding is formed between O of carbonyl group (-C=O) and h of –NH- group in
proteins.
3. Disulphide bridges/bonding:
The disulphide bonds occur only in sulphur containg protein. In these –SH- group are bonded to form
disulphide linkage,–H-S-S-H
Q4. a.Define the term Lipid?
Ans: Lipid:
Origin of word lipid: the word lipid is derived from Greek word lipose which means fat.
Definition: lipids are defined as biological molecules obtained from plant and animal tissue which are
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 55

not soluble in water but are soluble in non-polar organic solvents, such as alcohol, chloroform, ether
etc.
Composition of lipids: lipids are generally composed of carbon, hydrogen and oxygen. Generally,
lipids are esters of long chain fatty acids and alcohols. These esters are made up of three fatty acids,
therefore they are called triglycerides.

4. b. Distinguish between fats and oils.

Ans:

Fats Oils

Those triglycerides which contain higher Those triglycerides which contain higher
proportion of saturated fatty acidscomponents are proportion of unsaturated fatty acids components
called fats. are called oils.

They are solid or semi-solid at room temperature They are liquid at room temperature

Fats are mainly present in animals. Fats are mainly present in plants and fish.

Fats have high melting point Oils have low melting point

4 C. List four foods you eat that contain lipids.

Ans: Food that contain lipids:
foods that contain lipids are Milk, butter, Peanut, groundnut, walnut and coconut.
4. d. How lipids are important to our body?
Ans: Important functions of Lipids: lipids perform many important function in the body. Which are
given below;
1. Source of energy: The most important function is the long-term storage of energy. One gram of fats
contains approximately twice more energy than a gram of carbohydrates and protein.
2. Thermal insulator:
In mammals, a layer of fats is present under the skin. This layer acts as a thermal insulator. They
insulate the body from excessive heat or cold.
3. Protective layer:
the fatty tissue in our body are made from lipids. A protective layer of fat around our heart, kidneys
etc. reduces the impact of any external jerk or shock.
4. Regulatory hormone:
lipids such as Cholesterol etc. act as hormones to regulate body function.
Q4.a. how would you justify DNA as a genetic code of life?
Ans; DNA has the ability to store and transmit genetic information. The genetic information for the
cell are present in DNA. The genetic information for the cell are present in the form of special codes.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 56

These molecules are translated and expressed by synthesis of specific proteins. These proteins perform
various function according to the direction which are given by the codes present in DNA.

4. b. Distinguish between DNA and RNA.

Ans:

DNA RNA

DNA is double-stranded structure RNA is single-stranded structure

In DNA the pentose sugar is deoxyribose In RNA the pentose sugar is ribose

In DNA the nitrogen bases are adenine, cytosine, In RNA the nitrogen bases are adenine, cytosine,
guanine and thymine guanine and uracil

4. c. Explain the function of DNA.

Ans: Function Of DNA:
Genetic information: DNA has the ability to store and transmit genetic information. The genetic
information for the cell are present in DNA. The genetic information for the cell are present in the
form of special codes.
Protein synthesis: DNA also instructs how to synthesize a particular protein from a particular amino
acids. These instruction are known as genetic code.
Mutation: Mutation is a sudden chemical change in a DNA molecule that can lead to the synthesis of
protein with different amino acid sequence a DNA molecule that can lead to the synthesis of protein
with different amino acid sequence. Changes in DNA molecules. Changes in DNA molecules may be
caused by mutagens like radiations, chemical agents or viruses.
Q5.a. Define the term Vitamins and classify it.
Ans: Vitamins:
Origin of word vitamin: The word vitamin was originally vitamin, because the first one that was
found was amine hence the name vital amine or vitamin, subsequently studies of other such substances
showed that they were not all amine, so the “e” were dropped.
Definition of vitamin: Vitamins are organic compound that cannot be synthesized by an organism but
are very essential for the maintenance of normal metabolism and therefore must be included in the diet.
Classification of vitamins:
There are two types of vitamins.
i. Fats soluble vitamins ii. Water soluble vitamins
i.Fats Soluble Vitamins:
Vitamins which dissolve in fats are called fat soluble vitamins. These vitamins are vitamins A,
vitamins D, vitamins E and vitamins K.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 57

ii. Water Soluble Vitamins:

Vitamins which dissolve in water are called water soluble vitamins. These vitamins are B-complex and
Vitamin c. Vitamin B–complex include eight vitamins i.e. B1, B2, B3, B5, B6, Boltin, Folic acid and
B12.

Q5.b.Explain the importance sources of vitamins.

Ans: Sources of different vitamins are given below.
Sources of vitamin A: Vitamin A is found in milk, butter, fish oils, eggs, fresh green vegetables and
fruits.
Sources of vitamin B: Vitamin B is found in bread, rice, yeast, liver, milk, meat, fish, eggs, soybean
oil, and fresh green vegetables.
Sources of vitamin C: Vitamin C is found in citrus fruits (oranges, lemons) tomatoes, fresh green
vegetables.
Sources of vitamin D: Vitamin D is found in milk, butter, eggs, fish oils, vegetables.
Sources of vitamin E: Vitamin E is found in bread, rice, eggs, liver, butter, fresh green vegetables,
and corn and soybean oil.
Sources of vitamin K: sources of vitamin K are fresh green vegetables, liver, egg yolk, meat and
cheese.
Q5.c. Write down the names of five Vitamins and their importance.
Ans: Importance of vitamins:
there are different vitamins present in our body. Each vitamin plays an important role the development
and growth of our body. Importance of different vitamins are given below.
Importance of vitamin A: Vitamin A is necessary for vision. It also keeps the cornea moist.
Importance of vitamin B: Vitamin B helps to regulate nerve impulse transmissions.
Importance of vitamin C: Vitamin C is necessary for the formation of blood, improvement of the
immune system and protection against illness, including the common cold.
Importance of vitamin D: Vitamin D regulates blood calcium, necessary for proper bones and tooth
growth.
Importance of vitamin E: Vitamin E has been considered responsible for youth preserving and
defender against the carcinogenic (cancer-causing) effects of certain chemicals.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 58

TOPIC WISE QUESTIIONS

Q1. Write the sources of carbohydrates.
Ans: Sources of carbohydrates:
Carbohydrates are the most abundant class of Carbon, hydrogen, and oxygen containing compounds. It
ranges from simple to complex units.They have varied sources.
Sources of monosaccharides: they are found in fruits, vegetables and cereals. They are also found in
honey.
Sources of disaccharides: Sucrose are present in sugarcane, sugar beet, and fruits (mango,
pineapple). Lactose are found in milk and dairy product and maltose are present in cereals.
Sources of Polysaccharides: Polysaccharides are cellulose and starch.
Cellulose is obtained from plants, for example, cotton is pure cellulose.
Starch is found in cereal crops, for example, potatoes, wheat, barely, maize, rice etc.
Q2. Define and explain term protein...Ans: Origin of word protein: The word protein is derived
from Greek word “Proteios” which means of prime importance, because they are essential for the
growth and maintenance of life.
Definition: The complex nitrogenous compounds that are made up of amino acids present in all living
organisms.
Composition of Protein: Proteins consist of carbon, hydrogen, oxygen, nitrogen and sometime
consists of sulphur. About 50-55% of the dry weight of the cell is made up of proteins.
The building block of proteins:
The building block of proteins are amino acids.Amino acid is an organic compound having central
carbon atom called alpha carbon, which is attached to basic amino group (NH2), acidic carboxyl group
(COOH), a side chain alkyl group (R) and hydrogen atom.

Amino acids are joined together by peptide linkage in protein polymer.

Q3. Write down the sources of Lipids. Sources of Lipids: Lipids obtained from animals, plants and
marine organisms. For example, salmon and whales are rich source of cod liver oil.
Animal’s sources: Milk is a rich source of animal fat from which butter, ghee, cheese etc. are
obtained.
Plants Sources: seeds of many plants such as sunflower, corn, cotton, peanut, ground nut, walnut,
coconut etc. are good source of lipids.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 59

Q4. What is nucleic acid? Describe its composition, types and uses.
Ans: Nucleic acid:
Discovery: nucleic acid were first discovered in the nuclei of white blood cells in 1868 and in sperm
head in 1872 by Johannes Friedrich Miescher, a Swiss physician and biologist.
Definition: Complex organic compound consisting of nucleotides which synthesize proteins and
transmit characters from parents to offsprings are called nucleic acid.
Explanation: Nucleic acid are found in each and every living cell as well as in viruses. They are
essential part of genes.
Composition of Nucleic acid: Nucleic acid are composed of units called nucleotides. These
nucleotides are composed of three distinct parts:
i. Sugar: nucleotides consists of five carbon sugar which may be ribose (RNA) or deoxyribose (DNA).
ii. A nitrogen-containing bases of five types, uracil, cytocine, thymine, adenine and guanine.
iii. Phosphate group: Third part is phosphate group. .
Types of nucleic acid: Naturally occurring nucleic acid are of two types.
i. Deoxyribonucleic acid (DNA) ii. Ribonucleic acid (RNA)
i. Deoxyribonucleic acid (DNA):
Discovery: DNA was first discover by Watson and Crick in 1953.
Definition: DNA is a double-stranded structure composed of deoxyribose sugar, phosphate group and
four nitrogenous bases. The four nitrogenous bases present in DNA are adenine, cytocine, thymine,
and guanine.
Explanation: pentose sugar and phosphate group make the back bone of each strand. Two strand are
linked together through bases. The strands are held together by hydrogen bonds.
Function of Nucleic acid:
Function of DNA:
Genetic information: DNA has the ability to store and transmit genetic information. The genetic
information for the cell are present in DNA. The genetic information for the cell are present in the
form of special codes.
Protein synthesis: DNA also instructs how to synthesize a particular protein from a particular amino
acids. These instruction are known as genetic code.
Mutation: Mutation is a sudden chemical change in a DNA molecule that can lead to the synthesis of
protein with different amino acid sequence a DNA molecule that can lead to the synthesis of protein
with different amino acid sequence. Changes in DNA molecules. Changes in DNA molecules may be
caused by mutagens like radiations, chemical agents or viruses.
Function of RNA:
RNA is responsible for directing the synthesis of new proteins. RNA receives, reads, decodes and uses
genetic information from DNA to synthesize
Q5. Briefly describe the sources and deficiency symptoms of Vitamin A.
Ans: Vitamin A.
Vitamin A is fat soluble which is important for growth, vision and immune system.
Sources:
Vitamin A is found in milk, butter, fish oils, eggs, fresh green vegetables and fruits.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 60

Deficiency Symptoms:
Deficiency of Vitamin A cause night blindness, dry skin, burning and irritation of eyes.
Vitamin B Complex.
Vitamin B Complex is water soluble and consist of Vitamin B1, B2, B3, B5, B6, Boltin, Folic acid and
B12. They are important for energy production, nerves and cells,
Sources: Vitamin B is found in bread, rice, yeast, liver, milk, meat, fish, eggs, soybean oil, and fresh
green vegetable.
Deficiency Symptoms:
Deficiency of Vitamin B cause skin diseases, tongue/lips inflammation, anemia, bleeding gums and
beriberi.
Vitamin C.
Vitamin C is water soluble which is important for blood vessels, gums, healing wounds and preventing
cold.
Sources:
Vitamin C is found in citrus fruits (oranges, lemons) tomatoes, fresh green vegetables
Deficiency Symptoms:
Deficiency of Vitamin C scurvy and pain in joints.
Vitamin D.
Vitamin D is fat soluble which is important for bones and teeth.
Sources:
Vitamin D is found in milk, butter, eggs, fish oils, vegetables.
Deficiency Symptoms:
Deficiency of Vitamin D cause Rickets, osteomalacia.
Vitamin E.
Vitamin E is fat soluble which acts as an antioxidant.
Sources:
Vitamin E is found in bread, rice, eggs, liver, butter, fish, soybean oil, and fresh green vegetables.
Deficiency Symptoms:
Deficiency of Vitamin E causes anemia and sterility.
Vitamin K.
Vitamin K is fat soluble which is important for blood clotting.
Sources:
Vitamin K is found in liver, egg yolk, meat, cheese, fresh green vegetables.
Deficiency Symptoms:
Deficiency of Vitamin D cause Rickets, osteomalacia.
CHEMISTRY
Class 10th (KPK)

NAME: __________________________

F.NAME: _________________________

CLASS:___________ SECTION: ________

ROLL #: _____ SUBJECT: ____________

ADDRESS: ___________________________________

__________________________________________

SCHOOL: _____________________________________

https://web.facebook.com/TehkalsDotCom/

https://tehkals.com/
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 61

CHAPTER 14
ENVIRONMENTAL CHEMISTRY
Q1: How ozone layer is depleted in the atmosphere?
Ans: Ozone layer depletion:
Ozone is present in the stratosphere layer helps to absorb ultraviolet ray. when ozone depleting
substance such as chlorofluorocarbons (CFCs), Hydro chlorofluorocarbons (HCFCs) and volatile
organic compound goes to stratosphere layer react with uv-ray .This reaction breakdown the depleting
substances and release the free cl atom. This free cl atom reacts with ozone gas and deplete the ozone
layer.
Q2: Differentiate between primary and secondary pollutant. Write the name and sources of
greenhouse gases to atmosphere.

: Primary pollutant Secondary pollutant

Primary pollutant is an air pollutant which are Secondary pollutant is not produced directly.
released directly into air. Secondary pollutant are formed from primary
pollutants.

Example: Example:
The gases like SO2 released from burning
Photochemical oxidants, secondary
fossil fuel. Carbon Ammonia etc
particulate matter

The product which escape from the chimney Acid rain, like SO2 mix with water in
of industrial unit. Exhaust of automobiles. atmosphere and cause acid rain.
Nitrogen oxide and hydrocarbon react with
sunlight cause ozone

Greenhouse gases name:

The greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous
oxide and ozone.
Sources: The main sources of greenhouse effect is human activities. The main human sources of
greenhouse gas emissions are, fossil fuel, Deforestation, intensive livestock farming, use of synthetic
fertilizers and industrial processes, natural processes like animal and plant respiration.
Q3. Define Environmental Chemistry and atmosphere.
Ans: Environmental Chemistry:
The branch of chemistry which deal with the study of environment and the changes occurring in it, is
called environmental system.
Atmosphere: the thick protective blanket of air or gases around the earth, which helps to sustain life,
is called atmosphere.
Composition: The major constituents of atmosphere are N2 and O2. Its minor constitutions are CO2,
Noble gases and some trace gases.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 62

Q4. Sketch and briefly discuss the composition of atmosphere, by mentioning the percentage of
each component.
Ans: Sketch of atmosphere:

Percentage of each component:

Element Chemical Formula Percentage

Nitrogen N2 78.084

Oxygen O2 20.95

Argon Ar 0.93

Water H2O 0.0 - 0.4

Carbon dioxide CO2 0.00397

Neon Ne 0.0018

Helium He 0.000524

Ozone O3 0.00006

Krypton Kr 0.000114

Hydrogen H2 0.01

Q5. How the acid rain effect the building material or statues?
Ans: Acid rain: The rain having PH less than 5.6is called acid rain.
Effect of acid rain on building materials: Acid rain damages building material such as steel, paint,
plastic, cement sculptural work, material especially of marble and limestone.
CaCO3 +H2SO4 → CaSO4 +CO2 + H2O
The calcium sulphate is soluble in water and washed away with rain water.
The historical statues in Greece and Italy and The Taj Mahal in India were damaged due to acidic rain.
Q6: Increase in concentration of CO2 cause greenhouse effect, justify it.
Ans: As we know that CO2 is produced by burning fuels like oil, natural gas , diesel and organic
petroleum.CO2 is released to the atmosphere where it remain for many years. This leads to an
increasing concentration of CO2 in our atmosphere. Which in turn cause average temperature on earth
to raise. The CO2 is greenhouse gas which emission causes global warming.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 63

Q7: Briefly discuss how the acid rain affect the aquatic life.
Ans: Effect of Acid rain on aquatic life:
The rain which PH is less than 5.6 is called acid rain. The aquatic life like fish, plants and
microorganism are very sensitive to acidity .i.e. at PH-5, most fish eggs cannot hatch. Some adult fish
die. Ia fish or animal survive in acidic water but food they eat might not be available as food. i.e., frog
can tolerate the condition at around PH-4 but mayflies the food of frog are more sensitive and not
survive below PH-5.6.
Q8: List the sources which produce CO and CO2 to the atmosphere.
Ans: The following are sources which produced CO and CO2 to atmosphere.
CO: Natural sources: CO is one of the gaseous pollutant .its natural sources are Volcanic eruption,
Natural gas emission and forest fires. .
Anthropogenic sources: Most of carbon monoxide released to atmosphere by human activities.
Automobile release 75% of CO to the environment. Besides this incomplete combustion of fossil fuels,
smoking, forest fires and steel industries are the main sources of carb on monoxide.
Sources of CO2:
the main sources of carbon dioxide gas emission are our everyday activities such Cooking and baking
etc. vehicle and industrial emission, petroleum production and thermal power plant are also the source
of CO.
Q9: what are the adverse effects of global warming?
Ans: Global Warming: The gradual increase in the average temperature of the earth due to emission
of greenhouse gases is called global warming
Effect of Global warming:
Global warming is a phenomenon of climate change characterized by general increase in average
temperature. It is adversely effecting sea level, ozone layer, crop yield, precipitation (rain and snow
fall) and health.
Global warming is harming the environment in several ways include
Desertification increase in temperature around the world changes the water cycle and rainfall patterns
which causes desertification of certain areas.
Increases melting of ice and snow:
Snow and ice are melting at a faster pace due to increase in temperature.
Sea level rise:
Increase in temperature cause ocean waters to expand on other hand glaciers and ice are melting due to
rise in temperature which rise the sea level.
Strong storms and cyclone:
Rise of temperature also increase the frequency of strong cyclone and strong storms
Q10:What is the importance of ozone?
Ans: Ozone : Ozone is an allotropic form of oxygen, consisting of three chemically bonded oxygen
atoms
Importance of ozone:
The ozone acts as a protective layer in the atmosphere. it save earth and living thing from harmful UV
rays from sun.it also helps to remove the pollutant from the surface of the earth.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 64

Long questions
Q1: Sketch and identify the different layer of atmosphere.
A: Definition:
The layer of gases surrounding the earth is called atmosphere.it extends up to about 500km from the
earth’s surface.
Layers of Atmosphere:
The atmosphere is divided into four layers based on the variation in temperature in each layer.
(i) Troposphere
(ii) Stratosphere
(iii) Mesosphere
(iv) Thermosphere / Ionosphere
Troposphere :
The first layer of the atmosphere which is closest to Earth’s surface is called troposphere .we live in
this layer.it contains approximately 75% of atmosphere mass and 99% of total mass of water vapor
aerosol.
Characteristics of Troposphere :
The few characteristics of Troposphere are given below:
a. Height:
The average height of this layer from the earth’s surface is about 11km.It height is depends upon the
latitude and season and pressure. It is lowest over the poles and highest at equator and by season it is
lower in winter and higher in summer. The pressure, moisture content, density of air also decrease with
height
b. Main components:
The major components of this layer are N2, O2, and water vapours.70 to75% of the atmosphere gases
are present in this layer. Dust, particles are also present here.
phenomenon occurring in Troposphere:
All the weather phenomenon like cloud formation, winds, rainfall, snowfall takes place in this layer.
Lapse rate:
The change in temperature of atmosphere with increase in height is called lapse rate. It may be positive
or negative
Positive lapse rate:
If the temperature increase with height it is called positive lapse rate.
Negative lapse rate:
If the temperature decrease with height it is called negative lapse rate.
The air of this layer is warmer than other layers because it is heated from the earth’s surface below.
D. Temperature:
The temperature range of this layer is from 15℃to -56. ℃. It shows negative laps rate.
ii. Stratosphere:
The layer which is above the Troposphere is called Stratosphere.
It is second layer of the atmosphere. It is warmer at top than bottom. The lower portion has nearly
constant temperature with height but upper part temperature increase with latitude.
Characteristics of Stratosphere
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 65

a. Height:
The height of this layer is from 11km to 50 km.
b. Temperature:
The temperature of this layer is increases from -56℃ to -2℃ with height.
c. Main component:
The major component of this layer is ozone O3.
Ozonosphere:
Stratosphere contains ozone, at height of about 30 km, therefore it is called ozonosphere.
Production of ozone:
when the oxygen molecules absorbs ultraviolet radiation, it decompose to form oxygen atom. This
oxygen atom react with another oxygen and ozone is produced.
O2(g) + O●(g) → O3(g))
Phenomenon occurring in Stratosphere:
The ozone layer is present in this layer which absorbs harmful UV radiation .Thus protects the living
organism from harm full UV radiation.
The CFCs and ultra violet radiation from the sun, break down the Ozone molecule into mono atomic
oxygen and diatomic oxygen, resulting in damage to ozone layer.
O3(g)) ) →O2(g) + O●(g)

b. Differentiation between Troposphere and Stratosphere?

Ans:

Troposphere Stratosphere

The main component of this layer is N2, O2 The main component of this layer is ozone.
andCO2and water vapor

It is warmer than Stratosphere It is colder than troposphere.

The air density is more in this laye The air is less dense in this layer.

Clouds formation, rain, snowfall, and winds No clouds formation, rain, snowfall and wind
occur here.

The temperature is from 15 to -56. The temperature is from -56 to -2

Q2.a.Air is polluted in the big cities of Pakistan, justify the statement.

 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 66

Ans: Air pollution: According to world health organization (WHO), air pollution is defined as:
the substances released to air either by human activities or by natural activities, in sufficient
concentration to cause harmful effects to human beings, plants and other living thing is called Air
pollution.
Explanation: Air pollution change the physical, biological and chemical characteristics of airthat
cause adverse effects on human and other organism.
Air pollution in Pakistan: The big cities of Pakistan like Karachi, Lahore, Faisalabad and Islamabad
faces the air pollution due to following reasons.
1. Urbanization and population growth
2. Increase in number of vehicles used daily
3. Deforestation for making house and other uses.
4. Inefficient use of energy
5. Burning of garbage and plastic increase the smog and other air pollution due to worst air quality.
Q2.b.Enlist the main source of air pollution.
Ans: Pollutants: The substances that are responsible for causing air pollution are called air pollutant.
Sources of air pollution:
A: There are two main sources of air pollution.
i. Nature sources
ii. Anthropogenic/ man made sources
Natural sources: Natural sources of air pollutants are as follow,
A. Particulate:
The particulate pollutant is produced naturally by volcanic eruption, soil erosion by wind, dust storms ,
natural forest fires and salts spray from oceans . The contribution of the natural sources towards the
particulate emission is greater than man made sources. It has been estimated that natural sources
releases millions of tones particulate matter in to air.
B. Oxides of carbon (Coax):
CO and CO2 are the oxides of carbon.
I. Carbon monoxide;
The natural concentration of carbon monoxide in air is around 0.2 parts per million (ppm), and that
amount is not harmful to humans. Natural sources of carbon monoxide include volcanic eruption,
decomposition of organic matter, and electrical discharge during storms, seed germination and natural
gas emission etc.
ii. Carbon dioxide:
The natural sources of CO2 are animal and plants respiration, decomposition of organic matter, forest
fires and emissions from volcanic eruption.
iii. Oxides of nitrogen (NOx)
Bacteria and microorganisms are the main sources for emission of oxides of nitrogen into air. They
convert nitrates present in soil into oxides of nitrogen. Nitrogen oxides are produced naturally by
lightning, and atmospheric nitrogen gas into oxides of nitrogen and ammonia.
Iv. Oxides of Sulphur dioxides
The major oxides of Sulphur are Sulphur dioxide and Sulphur trioxide. They are produced by volcanic
eruptions, rock weathering and biological activities.
v. volatile organic compound:
Volatile organic compounds or VOCs, are chemicals that have a strong tendency to vaporize from
liquids or solids into gaseous states e.g. Methane. Wetlands are the largest natural source of methane.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 67

They contribute 78% of natural methane in the environment. Animals like sows, sheep and goats
during their normal digestion process produce large amount of methane.
Anthropogenic/man made sources:
The burning of different types of fuels by man that produced air pollution is called Anthropogenic
/man made sources.
I. Particulates:
Particulate matter is the sum of all solid and liquid particles suspended in air. The man-made sources
of particulate matter are combustion of fuels wood burning, construction, mining and industrial
process. ii.
Oxides of carbons;
a. Carbon dioxide:
Carbon dioxide is also added to the atmosphere through human activities, such as the burning of fossil
fuels and forests and the production of cement. Also thermal power generation and our everyday
activities such as cooking and baking released CO2.
Carbon monoxide:
CO is produced by incomplete combustion, i.e. when there isn't enough oxygen to make CO2,
Automobiles exhausts, smoking forest fires and steel industries are also the main sources of CO gas.
Oxides of nitrogen (NOx):
Automobiles exhausts, industrial activities, furnaces, thermal power generation. , jet airplanes are the
main sources of nitrogen oxides.
Sulphur oxides (SOx):
Burning of fossil fuels such as coal, oil and natural gas are the main source of Sulphur dioxide
emissions. Coal fired power stations, in particular, are major sources of Sulphur dioxide, other sources
of Sulphur dioxide are industrial processes and transportation.
Volatile organic compounds (VOCs):
Volatile organic compound e.g. methane is produced by burning fossil fuel.
Common sources of these organic compounds are:
Furniture polish and other wood finishing products
Solvents and thinners, e.g. nail polish remover with acetone or paint thinner.
Aerosols, such as air fresheners and other cleaners
Smoke from burning stoves or candle, as well as cigarettes.
Automobile exhaust and factories are also the main sources of VOCs.
Chlorofluorocarbons (CFCs) :
It is anthropogenic compounds that have been released into the atmosphere from various applications
such as in air-conditioning, refrigeration, blowing agents in foams, insulations and packing materials.
Q2.c. Prove that oxides of nitrogen and Sulphur cause air pollution.Oxides of Sulphur:
The major oxides of Sulphur are SO2 and SO3.
These oxides are produced by the burning of Sulphur containing fossil fuel. Sulphur dioxide is a gas. It
is invisible and has a nasty, sharp smell. It reacts easily with other substances to form harmful
compounds, such as sulfuric acid, sulphurous acid and sulphate particles. The main source of Sulphur
dioxide in the air is industrial activity e.g. the generation of electricity from coal, oil or gas that
contains sulphur. Sulphur dioxide is also present in motor vehicle emissions and air become
polluted.When sulphur dioxide combines with water and air, it forms sulfuric acid, which is the main
component of acid rain. Acid rain can:
Cause deforestation.
Effect the aquatic life and other organism life.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 68

Corrode building materials and paints.

Oxides of Nitrogen (NOx): Nitrogen dioxide and nitric oxide are oxides of nitrogen (NOx). When
nitrogen is released during fuel combustion it combines with oxygen atoms to create nitric oxide (NO).
This further combines with oxygen to create nitrogen dioxide (NO2). Nitric oxide is not considered to
be hazardous to health, but nitrogen dioxide is danger gas. NOX react with water, oxygen and other
chemicals to form nitric acids. It mix with water and other materials before falling to the ground and
cause acid rain NOx gases react to form smog.
2.d. Enlist the effects of air pollution.
Effects of air pollution: A variety of air pollutants have harmful effects such as;
i. carbon monoxide:
carbon monoxide reduce the amount of oxygen carried by hemoglobin around the body in
red blood cells. The result is that vital organs, such as the brain, nervous tissues and the heart, do not
receive enough oxygen to work properly. Breathing CO can cause headache, dizziness, vomiting, and
nausea.
ii. Carbon dioxide: carbon dioxide in the atmosphere increases the greenhouse effect. More thermal
energy is trapped by the atmosphere, causing the planet to become warmer than it would be naturally.
This increase in the Earth's temperature is called global warming
.iii. Sulphur dioxide: Sulphur dioxide affects human health when it is breathed in. It irritates the nose,
throat, and airways to cause coughing, wheezing, shortness of breath, or a tight feeling around the
chest .it reduced the productivity of plants and yellowing it.SO2 also damages the stone and marble.
iv. Nitrogen dioxide: NOx gases react to form smog and acid rain as well as being central to the
formation of fine particles (PM) and ground level ozone, both of which are associated with adverse
health effects. It reduces plant growth.it also effect the heart, respiratory system, skin and eyes.
V. Chlorofluorocarbons (CFCs): chlorofluorocarbons (CFCs) destroy the earth's protective ozone
layer, which shields the earth from harmful ultraviolet (UV) rays generated from the sun.
vi. Particulate matter:
It is toxic matter and affect both our lungs and heart.
Q3.what would be the result if rainwater is acidic?
Ans: Normal rainwater has a pH of 5.6 to 6. As we know that the air is polluted with the oxides of
nitrogen and Sulphur. When rainwater is exposed to the carbon dioxide and oxides of nitrogen and
Sulphur present in the atmosphere it become acidic and cause the acid rain. Acidic rain has a PH low
than normal rain. It has harmful effects on human, plants and materials. 5.6.Acid rain damages
building such as steel, paint , plastic ,cement sculptural work ,material especially of marble and
limestone.
For example
CaCO3 +H2SO4 → CaSO4 +CO2+H2O
The calcium sulphate is soluble in water and washed away with rain water.
The historical statues in Greece and Italy and The Taj Mahal in India were damaged due to acid rain.
(iii)
Q3.b.What could be done to minimize the formation of acid rain?
There are several solutions to stopping manmade acid rain
Energy conservation: The biggest step that we can take to prevent acid rain is to decrease our energy
consumption. Close the lights when we leave the room. Whenever we're not using an electrical
appliance, simply shut it off to conserve energy
Transportation: Because cars are a major contributor to acid rain pollution, it's important to find
alternate modes of transportation. By using public transit, carpools, bikes and even your feet, we're
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 69

helping reduce auto emissions...

Alternative fuels: An excellent way to prevent acid rain is to stop using non-renewable fuels and
switch over to renewable sources of energy, such as solar, wind and water energy. As the technology
for these alternative energies increases, they will become more accessible to the public. A great way
to reduce acid rain is to produce energy without using fossil fuels.

Q3.C. write down the effect of acid rain on,

i. Human (ii) Plants (iii) Soil (IV) Materials
i Human: The acid rain damages the, skin and hair of human beings. It also encourages lungs
problems, like asthma and bronchitis. Acid rain increases the acidity of water and cause the waterborne
diseases. (ii)
Plants: Acid rain removes the minerals and nutrients from the soil which is important for plant growth.
Young rootlets and leaf shoots are very sensitive to low PH at high altitudes acid fog and clouds
decrease the nutrients from trees and plant and their leaves become brown or dead. They are unable to
absorb sunlight and week to survive at freezing point.
Soil: Acid rain increase the acidity of soil and increase the amount of aluminium in soil which effect
the plant growth.
(iv).Material: The rain which have PH 5.6 is called normal rain. Acid rain have PH less than.
Q4.a. Explain ozone layer depletion.
Ans Ozone depletion: The decrease in the concentration of the ozone in stratosphere below its normal
level is called ozone depletion.
Occurrence of ozone : ozone is present in the stratosphere layer helps to absorb ultraviolet ray. When
ozone depleting substance such as chlorofluorocarbons (CFCs), Hydro chlorofluorocarbons (HCFCs)
and volatile organic compound goes to stratosphere layer react with uv-ray. This reaction breakdown
the depleting substances and release the free cl atom. This free cl atom reacts with ozone gas and
deplete the ozone layer.
Q4.B. Where does ozone layer lie in the atmosphere?
An ozone layer is mainly found in the lower portion of the stratosphere, from approximately 30
kilometers above Earth, although its thickness varies seasonally and geographically.
Ozonosphere:.The stratosphere contain ozone layer so it is also called ozonosphere.
Q4.C. what evidence can you find that depletion of ozone occurs in the atmosphere?
Chlorofluorocarbons are the main class of chemical that depleted the ozone layer in the stratosphere.
Measurements reveal that emissions of these compounds are rising, .CFCs are highly stable, synthetic
chemicals that were used in various applications from the 1930s onwards — for example, as
propellants in aerosol sprays, solvents and refrigerants. CFCs could be destroyed naturally only in the
stratosphere, in a process that releases chlorine atoms. Each of these atoms would be able to destroy
many ozone molecules and severe ozone depletion was found over Antarctica alone, thus posing a
threat to the ozone layer.
O2 (g) +O’→O3
Q4.D. recommend few ways to protect ozone layer.
Protection of ozone
Avoid the consumption of gases dangerous to the ozone layer.
Minimize the use of cars and use public transport
do not use cleaning products that are harmful to the environment and to us.
Buy local products.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 70

Maintain air conditioners

Q5. Summarize the components of stratosphere and troposphere?
Main components of Troposphere:
The major components of this layer are N2, O2, and water vapours.70 to75% of the atmosphere gases
are present in this layer. Dust particles are also present here
Main component of stratosphere:
The major component of this layer is ozone O3.
Ozonosphere:
Stratosphere has ozone layer, at a height of 30 km, therefore it is called ozonosphere.
B. Describe ozone formation.
Ans. formation of ozone: ozone is formed naturally by chemical reactions involving solar ultraviolet
radiation (sunlight) and oxygen molecules.
3O2(g) → 2O3(g)
First step: solar ultraviolet radiation breaks apart one oxygen molecule (O2) to produce two oxygen
atoms (2 O)
O2(g) → 2O(g)
Second step: Each of these highly reactive atoms combines with an oxygen molecule to produce an
ozone molecule (O3). These reactions occur continually whenever solar ultraviolet radiation is present
the stratosphere. As a result, the largest ozone production occurs in the tropical stratosphere.

C. Greenhouse effect is good or bad for us, explain it.

Ans:Greenhouse effect is good: The greenhouse effect is essential for humanity to survive, without it
the earth would be far colder. This is because if there will be no greenhouse effect then harmful solar
radiations will destroy habitat on earth. Some greenhouse gases like carbon dioxide, water
vapor and ozone absorb those radiations, they repel harmful radiations back to space and distribute
good radiations in all directions. This effect also maintain the temperature on earth.
Greenhouse effect is bad: When greenhouse gases cause an increase in temperature by stopping out-
going radiation from leaving the Earth. This causes an imbalance between in-coming and out-going
radiation and leads to warming. This effect is responsible for change in climate, so if carbon dioxide (a
greenhouse gas) will be emit as it is emitting now then there will be disturbance in climate. This may
also result in rise in temperature and possibly melt glaciers which will increase water level on earth,
this is so dangerous for us.
Predict the outcomes of global warming.
Rising seas and increased coastal flooding: Global warming increases the temperature of earth. As
temperatures increase, more rain take place, increasing the risk of flooding events.
Longer and more damaging wildfire seasons: wildfires are increasing and wildfire season is getting
as temperatures rise. Higher spring and summer temperatures and earlier spring snow-melt result in
forests that are hotter and drier for longer periods of time.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 71

More frequent and intense heat waves: Dangerously hot weather is already occurring more
frequently than it did 60 years ago heat waves to become more frequent and severe as global warming
intensifies. This increase in heat waves creates serious health risks, and can lead to heat exhaustion and
heat stroke. An increase in extreme weather events: Global warming is increasing certain types of
extreme weather events, including heat waves, coastal flooding, extreme precipitation events, and
more severe.

Topic wise:

Q: What are the effect of ozone layer depletion?

Effect of ozone layer depletion:
Ozone layer depletion increases the amount of UV radiation that reaches the Earth’s surface.
Ultraviolet (UV) radiation from the Sun can cause a variety of health problems in humans, including
skin cancers, eye cataracts and a reduction in the ability to fight off disease. Furthermore, UV radiation
can be damaging to microscopic life in the surface oceans which forms the basis Some of its major
impacts on living things are given below:
Skin cancer: Exposure to UV rays from sun can lead to increased risk for developing of several types
of skin cancer due to damages of skin tissue. In minor cases, it causes sun burn.
Eye damage: UV rays are harmful for our eyes too. Direct exposure to UV rays can lead to Cataract
problems.
Damage to Immune system: Our immune system is also highly unsafe to UV rays. Increased
exposure to UV rays can lead to weakening of the response of immune system and even impairment of
the immune system in

Aging of skin: Exposure to UV rays can lead to acceleration of the aging process of our skin. We look
older than our actual age. It can also lead to photo allergy that result in outbreak of rashes in fair
skinned people.

Other effect on human: In humans, exposure to UV rays can also lead to difficulty in breathing, chest
pain, and throat irritation and can even lead to curb of lung function.

Effect on amphibians: UV rays affect other life forms too. It adversely affects the different species of
amphibians and is one of the prime reasons for the declining numbers of the amphibian species. It
affects them in every stage of their life cycle; from hampering the growth extreme cases.
and development in the larvae stage, deformities and decreases immunities in some species.
Effect on marine life: UV rays also have adverse effect on the marine ecosystem. It adversely affects
the planktons which plays a vital role in the food chain and oceanic carbon cycle. Affecting
phytoplankton will in turn affect the whole ocean ecosystem.
Effect on plants: UV rays will also affect the plants. UV radiations can alter the time of owering in
some plant species. It can also directly affect the plant growth by altering the physiological and
developmental processes of fl the plants.
Effect on material:Ozone depletion will cause many materials to degrade faster. These materials
include PVC (used in window and doorframes, pipes and gutters), nylon and polyester.
CHEMISTRY
Class 10th (KPK)

NAME: __________________________

F.NAME: _________________________

CLASS:___________ SECTION: ________

ROLL #: _____ SUBJECT: ____________

ADDRESS: ___________________________________

__________________________________________

SCHOOL: _____________________________________

https://web.facebook.com/TehkalsDotCom/

https://tehkals.com/
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 72

UNIT: 15

ENVIRONMENTAL CHEMISTRY II:WATER

SHORT QUESTIONS: -

Q: Identify the factor which are responsible for dissolving polar substance in water?
A: Factors affecting solubility:
Water because of its polarity and ability to form hydrogen bonds, water makes an excellent solvent,
meaning that it can dissolve different kinds of molecules.
Explanation: Water molecules have a polar arrangement of the oxygen and hydrogen atoms—one side
(hydrogen) has a positive electrical charge and the other side (oxygen) had a negative charge. This
allows the water molecule to become attracted to many other different types of molecules. Water can
become so heavily attracted to a different molecule, like salt (𝑁𝑁𝑒𝑒𝑁𝑁𝑙𝑙) that it can disrupt the attractive
forces that hold the sodium and chloride in the salt molecule together and, thus, dissolve it.

2: Explain why it is advisable to drink boiled water?

A: Water treatment process improves the quality of water. In the treatment process, the removal of
suspended and dissolved solids and kills the harmful bacteria and microbes, makes the water clean and
safer for drinking. If we drink the untreated or contaminated water, there is a great risk of being
seriously ill. Boiling water is a safe precaution to prevent waterborne diseases like diarrhea, Dysentery
cholera, and Typhoid fever etc. So it is always advisable to drink treated or boiled water.
3: Why ice floats on the surface of water?
A: The density of most of the solids and liquids increases with decrease in temperature. However,
water shows a unique behavior in this regard because of hydrogen bonding. A water molecule is made
from one oxygen atom and two hydrogen atoms strongly joined to each other. Water molecules are
also attracted to each other by weaker chemical bonds (hydrogen bonds) between the positively-
charged hydrogen atoms and the negatively charged oxygen atoms of neighboring water molecules. As
the water cools below 4 C, the hydrogen bonds adjust to hold the negatively charged oxygen atoms
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 73

apart. This produces a crystal lattice, which is commonly known as ice. When water is cooled down
below 4℃, its density decreases. At 0℃, the density of water becomes 0.91 g/cm. Thus, ice is lighter
than liquid water and therefore floats on the surface of water.

4: Explain the importance of water and its quality?

A: Water is an important requirement in our life. After air, the importance of water takes the second
place for survival on earth. Earth is the only planet in the solar system that contains water. It is very
difficult to survive even a few days without drinking water.
Water quality: It describes the condition of the water, including chemical, physical, and biological
characteristics. Water quality is measured by several factors, such as the concentration of dissolved
oxygen, bacteria levels, the amount of salt or the amount of material suspended in the water .it saves us
from many waterborne diseases. When water quality is poor, it affects not only aquatic life but the
surrounding ecosystem as well.
5: What is eutrophication? How does it pollute water?
A: Eutrophication: The excessive amount of nutrients such as nitrogen, phosphorous, nitrates etc. in
water bodies is called eutrophication. Eutrophication can have serious effects, like algal blooms that
block light from getting into the water and harm the plants and animals that need it. If there's enough
overgrowth of algae, it can prevent oxygen from getting into the water and creating a dead zone where
no organisms can survive. Hence this results in the death of aquatic animals.

6: How chemistry helps to maintain clean swimming pools?

A: Chemistry helps to maintain a clean swimming pool by killing bacteria and other microorganisms
by using chlorine based disinfectants. It can be easily applied, measured and controlled. It is fairly
persistent and relatively cheap. Chlorine itself does not kill when it is added into water, but it reacts
with water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl).Cl2(g) + H2O(l) →
HOCl(aq) + HCl(aq) Both kill microorganisms and bacteria by attacking the lipids in the cell walls and
destroying the enzymes and structures inside the cell, makes them harmless. HOCl is unstable and
produce atomic oxygen (O) which bleach the dyes and kill the germs by oxidations. Hypochlorous acid
is able to oxidize the organisms in several seconds.
HOCl(aq) → HCl(aq) +[0]
7: Make the distinction between soft and hard water?
Soft water: Soft water contains fewer minerals such as Sodium. The formula is H2O.Soft water is that
water, which easily produces good lather and does not scum with soap because it has less minerals
than hard water
Hard water: Hard water contains more minerals such as Calcium bicarbonate, Magnesium
bicarbonate, Calcium Sulphate, Magnesium Sulphate, Calcium Chloride and Magnesium Chloride.
The formula is D2O. Hard water is that water, which produces little lather and forms scum with soap.
Because of the high mineral quantity in hard water it leaves residue on things Due to the minerals
counteracting the soap particles will not forming the foaming.
8: Why water is universal solvent?
A: Water is called the universal solvent because more substances dissolve in water than in any other
chemical. This is due to polarity of each water molecule. The hydrogen side of water molecule carries
slight positive charge, while oxygen side carries slight negative charge. This helps water dissociate
ionic compounds into positive and negative ions. The positive part of ionic compound is attracted to
oxygen side of water while negative part is attracted to hydrogen side of water. For example, consider
what happens when salt dissolves in water. Salt is sodium chloride( 𝑁𝑁𝑒𝑒𝑁𝑁𝑙𝑙). The sodium portion of the
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 74

compounds carries a positive charge, while the chlorine part carries a negative charge. The two ions
are connected by an ionic bond. The hydrogen and oxygen in the water, on the other hand, are
connected by covalent bonds. Hydrogen and oxygen atoms from different water molecules are also
connected via hydrogen bonds. When salt is mixed with water, the water molecules orient so that the
negative charge oxygen anions faces the sodium ion, while the positive-charged hydrogen cations face
the chloride ion. Although ionic bonds are strong, the net effect of the polarity of all the water
molecules is enough to pull the sodium and chlorine atoms apart. Once the salt is pulled apart, its ions
become evenly distributed, forming a homogeneous solution.

9: Give some of the disadvantages of the detergents?

A: Disadvantages:
1).The major disadvantage of detergent is that they are non - biodegradable. Microorganisms like
bacteria cannot decompose detergent, while these microorganisms can easily decompose soap.
2) They causes soil and water pollution
3) Excessive alkalis used in some detergent can damage the fabric.
4) Colour may run out while using cheaper variety of detergent.
5) More amount of water is required for rinsing to remove foam, otherwise it will damage the fabric
10: Identify the different toxic substances in household wastes?
A: Household waste products that contain corrosive, toxic, ignitable, or reactive ingredients are
considered to be "household hazardous waste". It is hazardous to human health and the environment.
The following are the toxic household waste substances: Aerosols, Batteries, Automotive, Chemicals,
Fertilizer, Fluorescent light bulbs, Hair color, Kerosene, Lawn and garden pesticides Nail polish,
Shampoo and Thermometers with mercury
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 75

LONG QUESTIONS:

1a): Enlist the main sources of water?

A: Water is one of the most abundant natural resources present on earth. There are two main sources of
water;

1. Oceans (97.5%)

2. Fresh water (2.5%) Fresh

water is further subdivided into:
Lakes
Rivers
Ground water
Glaciers and ice caps.
The distribution of water on the Earth’s surface is extremely uneven. Only 2.5% of water on the
surface is fresh; the remaining 97.5% resides in the ocean. Of freshwater, 69% resides in glaciers, 30%
underground, and less than 1% is located in lakes, rivers, and swamps. Only one percent of the water
on the Earth’s surface is usable by humans, and 99% of the usable quantity is situated underground.
b): How would you categorize physical properties of water?
A: Physical properties of water:
Pure water is colourless, odourless and a tasteless liquid.
Water exists in nature in all the three states i.e. solid, liquid and gas.
Freezing point of water is 0°C and boiling point is 100°C.
Pure water is neutral to litmus. It does not change the colour of the litmus.
Pure water has minimal electrical conductivity, but it’s conductivity increases as electrolyte dissolved
in it. Water is a polar molecule.
It has heat capacity of 4.18J/g℃ Water conduct heat and have high surface tension.
C): Predict the product of reaction, (i). K (ii). Cl2 (iii). CaO (iv). CH3CHOOH (v). C, with water?
A: Reaction With Alkali Metals: Potassium (K) react with water forming potassium hydroxide
(KOH), and produce Hydrogen gas. 2K(s) + 2H2O (l) → 2KOH(aq) + H2(g)↑
Reaction with Chlorine: Chlorine gas reacts with water to produce hydrochloric acid (HCl) and
hypochlorous acid (HOCl). It produces atomic oxygen which can killed the germs by oxidation.
Cl2(g) + H2O(g) → HCl + HOCl(aq) HOCl(aq) → HCl(aq) + [O]
Reaction with Calcium Oxide: Water reacts with calcium oxide (quicklime) forming calcium
hydroxide (slaked lime).CaO(s) + H2O(aq) → Ca(OH)2(aq)
Hydrolysis Reaction: It is defined as the reaction in which H-OH bond of water molecule is broken
down by the action of salt with water. When salt is added into water the solution becomes basic or
acidic due to hydrolysis reaction. In this reaction water splits into H+ and OH- ions CH3COONa(aq) +
H2O(l) → CH3COOH(aq) + NaOH(aq) (Salt of weak acid) (weak acid)(Strong
Base)Reaction with Carbon: When steam is passed over a red-hot carbon, a mixture of hydrogen and
carbon monoxide, known as water gas is produced.
C(s) + H2O (g) → CO(s) + H2(g)↑
Red hot carbon Water Gas
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 76

2: Water is an excellent solvent. Explain how this property is beneficial for life but sometimes
harmful for us?
A: Water is the best-known solvent. It can dissolve more substances than any other solvent. Due to this
fact, it is termed as a universal solvent. This property is very beneficial for us but sometimes become
harmful for us, because mostly salts (pollutants) dissolve in water and cause water pollution. This
characteristic property of water is due to the following reasons;
i: Polarity of water molecules
ii: Hydrogen bonding in water
iii: Dielectric constant
i: Polarity of water molecules: The water molecule has polar structure. The hydrogen on one end of
the water molecule is partially positive.while the oxygen on the other end is partially negative. It is due
to the electronegativity difference between oxygen (O=3.5) and hydrogen (H=2.1) atoms. When an
ionic compound is added into water, oppositely charged ions are surrounded by water molecules.
These oppositely charged ions of ionic compounds are pulled by the water molecules and it becomes
soluble in water. For example,𝑁𝑁𝑒𝑒𝑁𝑁𝑙𝑙,𝐾𝐾𝑁𝑁𝑙𝑙, are soluble in water. When an ionic compound such as
sodium chloride (𝑁𝑁𝑒𝑒𝑁𝑁𝑙𝑙) is added to water, the sodium ion (Na+) of NaCl is attracted towards the partial
negative pole (O-δ) of water molecule while the chloride ion (Cl+) is attracted towards the partial
positive pole (H+𝛿𝛿 ) of water molecule. The ionic bond break down in NaCl, which causes the sodium
chloride to split in water and dissolves. The water molecules orient in such a way that the negative
poles are towards the positive ions. Similarly, the positive poles of water molecules orient themselves
around the negative ions. A hydration shell is formed around the ions, which prevents Na+ and Cl -
from attracting each other.
ii: Hydrogen bonding in water: Water molecule is composed of oxygen and hydrogen atoms. The
hydrogen on one end of the water molecule is partially positive .while the oxygen on the other end is
partially negative. Because of the presence of two nonbonding electrons (lone pairs of electrons) on
oxygen, water molecule forms four hydrogen bonds with other H2O molecule. These water molecules
are arranged in a tetrahedral manner. Hydrogen bonding makes water unique. Covalent compounds,
which have polar ends also form hydrogen bond with water. This behavior enables water to dissolve
some of the covalent compounds having hydroxyl group (OH˗) very easily. For example, sugar
(C12H22O11), alcohol like methyl alcohol (CH3OH) etc. will dissolve easily. iii: Dielectric constant:
Dielectric constant is based on the coulomb law in which the force of attraction between two
oppositely charged bodies “x” and “y” is directly proportional to the product of charges and inversely
proportional to the square of distance between them r2 .Mathematically it can be written as:
(𝒙𝒙)(𝒚𝒚) (𝒙𝒙)(𝒚𝒚)
𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭∞ 𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭 = Where D is the proportionality constant and is called the dielectric
𝑭𝑭𝒓𝒓 𝑫𝑫𝑭𝑭𝒓𝒓
constant of water. Greater the value of D the smaller will be the force of attraction and vice versa.
Water has a high dielectric constant of 80 at 18℃. Thus, the positive and negative ions of a polar salt
dissolved in water will have less force of attraction and would remain soluble, while other liquids have
small value of dielectric constant compared to water and therefore, these are not good solvents.3a):
Classify temporary hard water and permanent hard water?
A: There are two types of hard water;
1: Temporary hard water2: Permanent hard water
1: Temporary hard water: The temporary hardness of water is due to the dissolved Calcium
bicarbonate and Magnesium bicarbonate. These salts are soluble in water and are present in the form of
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 77

positive and negative ions as shown below:

Ca(HCO3)2(aq) → Ca2+((aq0 + 2HCO3-(aq) Mg(HCO3)2(aq) → Mg2+(aq)+ 2HCO3-(aq) 2: Permanent
hard water: The permanent hardness of water is due to the presence of chlorides (Cl-) or sulphates
(SO4-2) of calcium and magnesium i.e. MgCl2, MgCO3 and CaCl2. These salts are soluble in water and
produce the respective ions in water. Simple boiling of the water cannot decompose these
salts.CaCl2(aq) → Ca2+ + 2Cl-(aq)MgCl2(aq) → Mg2+ + 2Cl-(CaSO4(aq) ) → Ca2+((aq) + SO4_2(aq)
MgSO4 → Mg2+ + SO4_2(aq)b): What methods could be adopted to remove the temporary
hardness of water? A: Methods for Removal of Temporary Hardness:
i: By boiling the temporary hard water: Temporary hardness of water can be easily removed by
simple boiling the water. This hardness is caused by the presence of dissolved calcium bicarbonate,
Ca(HCO3)2, which decomposes on heating. The calcium carbonate (CaCO3) is formed. The calcium
carbonate is insoluble and settles down as precipitate at the bottom. , Ca(HCO3)2(aq)→ CaCO3(s) +
CO2(g)+ H2O(g) ii: Clark’s Method: This
method is used to remove the temporary hardness of water on a large scale. This is a chemical method.
A calculated amount of slaked lime, (Ca(OH)2) is added to the temporary hard water. The soluble
bicarbonate ions (HCO3-) of calcium and magnesium present in temporary hard water are converted
into their carbonate ions(CO3-2). The carbonates of calcium and magnesium are soluble in water and
settles down at the bottom. Ca(HCO3)(aq) + Ca(OH)2 → 2CaCO3(s)+ 2H2O(l)White ppt
Mg(HCO3)2(aq)+ Ca(OH)2 → MgCO3(s) + CaCO3(s) + 2H2O(l)White pptC): What methods could be
adopted to remove the permanent hardness of water? A: Methods for removal of
Permanent Hard: Permanent hardness
of water can only be removed by using chemicals, which convert soluble salts into insoluble salts on
precipitation. i:
By using washing soda: The washing soda (NaCO3) removes the permanent hardness of water. The
washing soda reacts with the soluble calcium and magnesium chloride and sulphate and converts them
into insoluble calcium and magnesium carbonate respectively
Na2CO3(aq) + CaCl2(aq) → CaCO3(s)+ 2NaCl(aq) Na2CO3(aq)+ MgCl2(aq) → MgCO3(a) +
2NaCl(aq)Na2CO3(aq) + CaSO4(aq) → CaCO3(s)+ Na2So4(aq) Na2CO3(aq)MgSO4(aq) →
MgCO3(s) + Na2SO4 (aq)ii: Ion exchange method: Zeolite is an ion exchange resin which is integral
part in the water treatment process in both consumer and industrial settings. Zeolite is naturally
occurring sodium aluminum silicates. It can also be prepared artificially. This resin is commonly
known as sodium zeolite. When hard water is passed through the resin, the sodium ions will go into the
solution while the unwanted calcium and magnesium ions take their place in the resin.
CaSO4(aq)+ Na2-Zeolite → Ca-Zeolite + + Na2SO4(aq) Soluble Insoluble
MgSO4(aq) +Na2-Zeolite → Mg-Zeolite + Na2SO4(aq) Soluble InsolubleWhen
the Na-zeolite is used up and becomes inactive then it can be regenerated by treating it with a strong
solution of common salt(NaCl).
Ca-Zeolite(S) + 2NaCl(aq)→ Na2-Zeolite(S) + CaCl2(aq)4a): Why water is important for us?
A: Water is an important requirement in our life. After air, the importance of water takes the second
place for survival on earth. Water is important for us because;
Water is vital for maintaining life. The reactions, which take place in our body and keep us alive occur
in the presence of water.
Water regulates the temperature of earth.
Water is a universal solvent, as many substances dissolve in it.
Water serves as a medium for transportation, as ships and boats move on water.
Water enables our body to excrete waste during perspiration and urination.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 78

The kidneys and liver use it to help flush out these wastes from our body.
Water is used in cooking and washing.
Running water is used to generate electricity.
Water in lakes, rivers and oceans are used as a means of transportation.
Fish and other aquatic animals and many plants live in water.
Agriculture needs large amount of water, to cultivate fruits, vegetables, and other food.
It is required for irrigating crops, as seeds cannot germinate without water.
Many industries such as petroleum, fertilizers, dye and drugs industries require large quantities of
water for various processes.
b): Write the disadvantages of hard water?
A: The following are the disadvantages of hard water;
Hard water consumes large amount of soap in washing process.
Hard water is unfit to use in steam engines and boilers. When hard water is used in the boiler, calcium
and magnesium salts settles down at the bottom as hard insulating scale. As a result, more fuel is
consumed in producing steam. If these are not removed, they block the tubes, which lead to the
engines. These make a constant threat to the explosion of boiler. This deposition of scales inside the
boiler causes overheating and reduces the life of boiler.
Use of hard water for drinking purposes for a long time causes dysentery, intestinal and stomach
diseases. If magnesium sulphate is present in the hard water, it weakens the stomach function.
c): Enlist the advantages of wastewater treatment?
A: Wastewater treatment is defined as the process of removing any harmful contaminants from water
no longer needed
Advantages of wastewater treatment:
1)It prevents disease:
It removes harmful bacteria and chemicals from water that cause disease. Thus makes the water safe
for living organisms.
It provides clean water: It filtering out harmful contaminants, and leaving a water source clean and safe
for everyone. This removes the fear of droughts, water shortages.
5a): How would you evaluate the effects of water pollution?
A: Effects of water pollution:
The effects of water pollutants are not only disturbing to people but also to plants, animals, fishes and
birds. Polluted water is unsuitable for drinking, agriculture and industry.
The major effect of water pollutants are as under;
i: Infectious disease: Water pollution is the major cause of infectious diseases in human beings. These
diseases include typhoid, cholera, dysentery, amoebiasis, ascariasis and hepatitis etc.
ii: Nutrient pollution: Nutrient pollution is a form pf water pollution. In this process, large amount of
nutrients such as nitrogen, phosphorus, nitrates etc. become part of water as a runoff from agricultural
fields or weathering of rocks. The enrichment of nutrients in water bodies is called eutrophication.
These excessive amounts of nutrients create problems such as excessive growth of algae, decrease in
dissolved oxygen in water etc. This in turn, can kill fish, carbs, oysters, and other aquatic animals.
iii: Chemical contamination: Some of the major effects of chemical contamination are as under;
Pesticides affect and damage the nervous system, liver, reproductive system, endocrine glands and
DNA etc.
Oil and petrochemical can alter the ecology of aquatic habitats and the physiology of marine
organisms. In human beings, it causes gastro-intestinal irritation, liver and kidney damage and nervous
system effects. Mercury and its compounds are used in many industries. It finds its way into
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 79

the water bodies primarily through air pollution and industrial wastes. Mercury gets into the body
through food especially seafood. In children, it causes brain damage, learning defects and incomplete
mental development. In adults, mercury causes Parkinson’s disease, Alzheimer’s disease etc.
iv: Thermal water pollution: Hot water from industrial processes is directly allowed to become the
part of the environment. This hot water effects the aquatic life in two ways;
a. The hot water decrease the solubility of oxygen as a result aquatic organisms will die due to the
shortage of oxygen. Many aquatic animals especially young cannot survive in water above 30℃ and
will die.

b.Explain how industrial wastes pollute environment?

A: Industrial wastes such as hot water, chemicals and solid materials pollute our environment in the
following ways;
Most of the industries have been started without proper planning and waste treatment plants. They just
dispose off untreated toxic wastes into nearby drains, canals or rivers. Industries produce lots of
wastes. These wastes are highly toxic due to the presence of compounds like mercury, calcium, lead,
chromium, arsenic, acids such as hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3),
oils, grease, dyes and may also contain gases in dissolved form.
Water used in industries as a coolant or for cleaning purposes dissolves all the chemicals and
detergents and causes water pollution when discharge from industries. These industrial wastes also
pollute ground water. The compounds which are discharged from industries gets into the body through
edible substances and cause different diseases.
Radioactive wastes that may leak from nuclear power stations also create many problems to the living
organisms.
c): Support the view that domestic wastes cause pollution?
A: Domestic Wastes: Domestic waste is also called solid waste or urban waste. It is either in solid or
semisolid form. It contains food, newspaper, glass bottles, cans, metals etc. Today, many people dump
their garbage into streams, lakes, rivers and seas. When rainwater or other forms of water come in
contact with these materials, it removes or extracts chemicals from these solid wastes. This process is
called leaching and the resulting mixture is called leachate. Leachate either seeps into the soil and
pollutes underground water or finds its way to rivers and streams through rainwater.
d): How would you relate the agricultural wastes and water pollution?
A: Agricultural Wastes: Agricultural wastes are wastes produced as a result of various agricultural
activities. Agricultural wastes include both natural and synthetic wastes. Natural (organic) wastes
include manure and other wastes from farming, harvesting, poultry and slaughter houses etc. whereas,
synthetic wastes consists of fertilizers in run-off water from fields, pesticides, insecticides and
herbicides that enter into water, air or soils and salt and slit drained from fields.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 80

Topic wise:

Composition of water: water is a compound of hydrogen and oxygen. Henry Cavendish proved that
water is a compound. Composition of water can be determined,
1) Volume 2) Mass .
Composition of water by volume: Water molecule composed of two Hydrogen atoms and one
Oxygen atom. Its molecular formula is H2O.Composition of water can be determined by using an
apparatus called "Hofmann voltammeter". When an electric current is passed through water containing
a little salt, water decomposes into hydrogen gas and oxygen gas.it shows that water composed of two

volumes of hydrogen and one volume of oxygen.

Composition of water by mass: Water is composed of one part of hydrogen to eight parts of oxygen
by mass. Joseph Proust determined the ratio of water by mass I.e. 1:8.
Explanation: One mole of H2O is made up of 2 moles of Hydrogen atoms and 1 mole of Oxygen atom
Mass of 1 mole of Hydrogen atoms= 1 g /mol
Mass of 1mole of Oxygen atoms = 16 g/mol
Mass of two moles of Hydrogen atoms = 2x 1 g/mol = 2 g/mol.
Mass of one mole of Oxygen atoms = 1 x 16 g /mol
Mass of one mole of water = 2 g/mol + 16 g/mol = 18 g/mol.
% of hydrogen = molecular mass of hydrogen / molecular mass of H2O ×100
%of hydrogen= 2/18 ×100=11.11
% of oxygen = Atomic mass of oxygen/molecular mass of H2O ×100
% of oxygen = 16/18=88.88
Ratio = 1 : 8
Water pollution:
Definition: water pollution occurs when undesirable foreign substance are introduced into natural
water. The substances that cause water pollution is called pollutants. Water pollution is one the main
environmental issues that we are facing, as more than 70% of the Earth’s surface is water-covered.
Sources of water pollution: The major sources of water pollution are following;
Industrial waste: waste from factories, refineries, waste treatment plants etc. that emit fluids of
varying quality directly into urban water supplies cause water pollution sources include contaminants
that enter the water supply from soils/groundwater systems and from the atmosphere via rain water.
Soils and groundwater contain the residue of human agricultural practices (fertilizers, pesticides, etc.)
and improperly disposed of industrial wastes. Atmospheric contaminants are also derived from human
practices (such as gaseous emissions from automobiles, factories and even bakeries).
Waterborne diseases: The diseases that spread due to polluted water or eating those foods that are
prepared from polluted water are called waterborne diseases. They bacterial, parasitic or viral diseases.
(1)Bacterial infections:
cholera: The symptoms are watery diarrhea and vomiting. It effects intestine and causes dehydration.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 81

Dysentery: It is the large intestinal disease, causing abdominal cramp, anal pain and bloody stool.
Typhoid: it is bacterial disease and person is suffer from typhoid fever.
(2) Viral infections:
Hepatitis A and E: Hepatitis-A virus infection (HAV) and Hepatitis E virus infection (HEV) are due
to contaminated water: it attack liver and cause jaundice.
Polio: Polio, also called poliomyelitis or infantile paralysis, is an infectious disease caused by the
poliovirus.The polio virus usually enters the environment in the feces of someone who is infected. In
areas with poor sanitation.
Protozoal infections: In this disease Amoeba enters through unsanitary food or contaminated water
effect the gastrointestinal illness.
Parasitic infections: Guinea worm and pinworm infection are common parasitic infection. In
contaminated water the egg of these worms are swallowed cause ulcers, fever, and vomiting.
Arsenicosis and fluorosis:
Fluorosis: It is an abnormal condition caused by excessive intake of water having fluorine.it effects
the bones and teeth.
Arsenicosis: Drinking water rich in arsenic over a long period leads to arsenic poisoning or arsenicos
is Most waters in the world have natural arsenic concentrations of less than 0.01 mg/dm3.The
symptoms of this disease are excess of saliva, vomiting, nausea and blood in urine.
CHEMISTRY
Class 10th (KPK)

NAME: __________________________

F.NAME: _________________________

CLASS:___________ SECTION: ________

ROLL #: _____ SUBJECT: ____________

ADDRESS: ___________________________________

__________________________________________

SCHOOL: _____________________________________

https://web.facebook.com/TehkalsDotCom/

https://tehkals.com/
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 82

UNIT 16
EXERCISE
SHORT QUESTIONS
Q1. How could you convert NaHCO3 into Na2CO3?
Ans: Calcination: sodium bicarbonate (NaHCO3) is converted into sodium carbonate (Na2CO3) by the
process called calcination, in this process NaHCO3 is heated in rotatory funnel call
calcinatory, to give anhydrous sodium carbonate.
2NaHCO3(s) → Na2CO3(s) + CO2 (g) + H2O
Q2. Enlist the different uses of urea?
Ans: Uses of urea:
it is a white crystalline organic compound. It is important due to the following usage.
1. Fertilizer: about 86% of urea is used as solid fertilizer.
2. Resins:Urea-formaldehyde resins are used as a polywood adhesive/glues.
3. Use as explosive:Urea can be used to make urea nitrate, which is highly explosive.
4. Chemical Industry:Urea is used as a raw material for manufacture of many important chemical
compounds like plastics, resins, and various adhesives etc.
6. Flame proofing agent:Urea is used as a flame proof in agent.
7. Cosmetics:it is used as an ingredient in hair conditioners, facial cleaners and lotions.
8.Repellent to Corrosion:It is used as an alternative to rock salt in the deicing roadways and runways.
It does not promote metal corrosion to extent that salt does.
9. Cigarette:It is also used as flavor enhancing additive for cigarette.
10. Medicinal uses:urea containing creams are used as tropical dermatological products to promote
rehydration of skin.
Q3. Differentiate between minerals and ore.
Ans: Minerals: The naturally combined state of metal is called is called mineral.
Ores: An aggregate of mineral and other impurities is known as ore.
Q4. What is metallurgy? What are its types?
Ans: Metallurgy: The art and science of making of making metals and alloys from their ores with
properties suitable for practical uses is called metallurgy. OR
The science that deals with the procedures used in extracting metals from their ores, purifying, alloying
metal sand creating useful objects from metal is called metallurgy.
Types of metallurgical operations: In metallurgy the ores are mined and subjected to various
mechanical and chemical processes. There is no single method for extracting metals from their ores,
But certain basic operation are , required that is,
i. Concentration of ores
ii. Extraction of metal (roasting and reduction)
iii. Refiningof metal.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 83

Q5. What is the function of forth floatation?

Ans: Forth floatation: A separating method of the mineral particles of ore from the gangue that
depends on the wetting of the minerals pieces.
Function of forth floatation: It is a process for selectively separating hydrophobic materials from
hydrophilic. In this process the ore is wetted with water. And the water insoluble impurities float on
the surface and thus separated from the ore.
Q6. On what basis the different fraction of petroleum are separated?
Ans: Fractional distillation: The type of distillation in which different fractions of petroleum are
separated according to difference in their boiling point is called Fractional distillation.
Basic principle of Fractional distillation: The fractions are separated according to difference in their
boiling point. The substances having less boiling points boils out first leaving behind others.
Q7. What is slaked lime? How slaked lime is produced.
Ans: Slaked lime: Slaked lime is calcium hydroxide Ca (OH) 2.
Preparation: when quick lime (CaO) and water are mixed together in calculated amount and the
mixture is heated, slaked lime is produced.
CaO + H2O → Ca (OH) 2
Q8. Assess the composition of urea and calculate the percentage of nitrogen in it.
Ans: Composition of urea: urea is one of the most important nitrogenous fertilizers. Its chemical
formula is NH2CONH2. The formula shows that urea is composed of nitrogen, hydrogen. Carbon and
oxygen. Percentage of nitrogen in urea:
Percentage of an element in a compound can be calculated by using following formula:
𝐴𝐴𝑖𝑖𝑐𝑐𝑚𝑚𝑖𝑖𝑐𝑐 𝑚𝑚𝑖𝑖𝑝𝑝𝑝𝑝𝑝𝑝 𝑐𝑐𝑜𝑜 𝑐𝑐𝑖𝑖𝑐𝑐𝑚𝑚𝑐𝑐𝑖𝑖𝑖𝑖 ×𝑖𝑖𝑐𝑐.𝑐𝑐𝑜𝑜 𝑖𝑖𝑖𝑖𝑖𝑖𝑐𝑐𝑚𝑚𝑝𝑝 𝑖𝑖𝑖𝑖 𝑐𝑐𝑐𝑐𝑚𝑚𝑝𝑝𝑐𝑐𝑝𝑝𝑖𝑖
Percentage of element = × 100
𝑚𝑚𝑐𝑐𝑖𝑖𝑐𝑐𝑐𝑐𝑝𝑝𝑖𝑖𝑖𝑖𝑐𝑐 𝑚𝑚𝑖𝑖𝑝𝑝𝑝𝑝 𝑐𝑐𝑜𝑜 𝑖𝑖ℎ𝑐𝑐 𝑐𝑐𝑐𝑐𝑚𝑚𝑝𝑝𝑐𝑐𝑝𝑝𝑖𝑖𝑝𝑝

Molecular formula of Urea = N2H4CO

Molecular mass of urea = 14×2 + 1×4 + 12 + 16 =
= 28+ 4+ 12 + 16 = 60g/mol.
Q9. What is gangue and where it is found?
Ans: Gangue: The earthy material like sand, rock, clay, lime stone, etc. attached with ores are called
gangue. Gangue are the impurities mostly found in ores
Q10. How blistered copper is purified?
Ans: Purification of blistered copper: The blistered copper is purified/refined by electrolytic process.
Electro-refining of Copper: the process of electro refining of copper involves following steps.
Construction:i. Anode: a large plate of blistered copper is made anode.
ii. Cathode: a thin sheet of pure copper is made cathode.
iii. Electrolyte: The solution of copper sulphate (CuSO4) and dil. Sulphuric acid (H2SO4) solution is
used as an electrolyte.
Working: During electrolysis, pure copper is deposited on the cathode.
The impurities (Ag, Au and Pt. along with Cu2O) in the anode and settle s\down at the bottom and are
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 84

removed as anode mud. The copper obtained by this method is 99.9% pure.
Reaction at anode: Cu(s) → Cu+2(aq) + 2e-
Reaction at Cathode: Cu+2(aq) + 2e- → Cu(s)
LONG QUESTIONS
Q1. How could you convert the concentration ore to its oxide?
Ans: Concentration ore to its oxide: Following methods are used to convert the concentration ore to
its oxide form.
1. Roasting: It is the process in which concentrated ore is heated alone or in the presence of some
other materials in excess of air in a process.
Procedure: the ore of metals such a copper and nickel when roasted in a furnace in the
presence of air between 50000C and 70000C are converted into their oxide i.e.
CuCO3(s) → CuO(s) + CO2 (g)
Cu (OH) 2(s) → CuO(s) + H2O (g)
2CuFeS2(s) → Cu2S(s) + 2FeS(s) + SO2 (g)
2. Smelting: It is the process in which the oxide ore in the fused state is reduced with reducing
agents such as coke to get the metal is called roasting.
Procedure: The roasted ore is mixed with coke and sand and smelted into blast furnace.
During smelting iron sulphide (FeS) get oxidized to iron oxide (FeO). The iron oxide then react
with silica (SiO2) forming iron silicate (FeSiO3).
2FeS(s) + 3O2 (g) → 2FeO(s) + 2SO2 (g)
FeO(s) + SiO2(s) → FeSiO3
Cuprous sulphide (Cu2S) is also oxidizes and form copper oxide (Cu2O).
2Cu2S + 3O2 → 2Cu2O + 2SO2 (g)
Cu2O then reacts with un-reacted FeS and form Cu2S and FeO.
Cu2O(s) + FeS(s) → Cu2S(s) FeO(s)
TheCu2Sand FeS is called matte and is removed through slag hole.
3. Bessemerization:
4. History: Bessemer process was invented by Henry Bessemer.
Bessemer converter: This process is carried out in a special kind of egg shaped or pear shaped
furnace. This furnace is called Bessemer.
Procedure: In Bessemerization matte is reacted with sand. Iron sulphide (FeS) oxidized to Iron oxide
(FeO). This iron oxide (FeO) reacts with sand (SiO2) forming (FeSiO3), slag which is float on the
surface.
2FeS + 3O2 → 2FeO + 2SO2
FeO + SiO2 → FeSiO3
Similarly Cuprous sulphide (Cu2S) is converted to cuprous oxide (Cu2O). This Cu2O reacts with Cu2S
to produce copper (Cu) in molten form and sulphur dioxide (SO2). This copper is known as blister
copper (95-97% pure).
2Cu2S + 3O2 → 2Cu2O + 2SO2
2Cu2O + Cu2S → 6Cu + SO2
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 85

Q1. b. How would you use the roasting in extraction of copper?

Ans: Roasting: It is the process in which concentrated ore is heated alone or in the presence of some
other materials in excess of air in a process.
Procedure: The concentrated ore of copper when roasted in a furnace between 50000C and 70000C in
the presence of air are converted into their oxide i.e.
CuCO3(s) → CuO(s) + CO2 (g)Cu (OH) 2(s) → CuO(s) + H2O (g)2CuFeS2(s) → Cu2S(s) + 2FeS(s) + SO2 (g)
Q1.c. What inference can you make of smelting in extraction of copper?
Ans: Smelting: It is the process in which the oxide ore in the fused state is reduced with reducing
agents such as coke to get the metal is called roasting.
Procedure: The roasted ore is mixed with coke and sand and smelted into blast furnace. During
smelting iron sulphide (FeS) get oxidized to iron oxide (FeO). The iron oxide then react with silica
(SiO2) forming iron silicate (FeSiO3).
2FeS(s) + 3O2(g) → 2FeO(s) + 2SO2(g)FeO(s) + SiO2(s) → FeSiO3
Cuprous sulphide (Cu2S) is also oxidizes and form copper oxide (Cu2O).
2Cu2S + 3O2 → 2Cu2O + 2SO2 (g)
Cu2O then reacts with un-reacted FeS and form Cu2S and FeO.
Cu2O(s) + FeS(s) → Cu2S(s) FeO(s)
TheCu2Sand FeS is called matte and is removed through slag hole.
Q1. D. can you elaborate the reason of electro-refining of copper?
Ans: Purpose of electro-refining of copper: The blistered Copper is 95-97% pure copper, beside,
this it contains iron (Fe), manganese (Mn), silver (Ag), gold (Au) etc. copper when used for electrical
industries must be highly pure. Therefore in order to purify the blistered copper the electro-refining of
copper is done.
Q2. A. List the raw materials used in Solvay process?
Ans: Solvay process: Sodium carbonate which is also known as soda ash is commercially prepared by
a process known as Solvay process.
Raw materials used in Solvay process: Raw materials used for the manufacture of sodium carbonate
are:

• Sodium chloride (NaCl)

• Lime stone (CaCO3)
• Ammonia (NH3)
• Water (H2O)
Q2.b. What basic reaction would you use to support the manufacture of soda ash?
Ans: Basic reaction:
Solvay process consists of following steps.
1. Preparation of Brine solution: At first step, a saturated solution of sodium chloride is prepared
which is known as brine.
2. Preparation of ammoniacal Brine: In this step, saturated brine solution is allowed to flown down
in ammoniating tower, where ammonia is dissolved in brine.
3. Preparation of carbon dioxide and Slaked lime: Carbon dioxide is produced by heating limestone
in lime kiln. CaCO3(s) → CaO(s) + CO2 (g)
Carbon dioxide is fed into the carbonating tower from top. Calculated amounts of quick lime (CaO)
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 86

and water mixed to produce slaked lime Ca (OH) 2 (aq)

CaO(s) + H2O → Ca (OH) 2(aq)
4. Carbonation of Ammoniacal brine: in this step, ammoniacal brine is allowed to enter the
carbonating tower, where ammoniacal brine is mixed with carbon dioxide gas, carbon dioxide reacts
with ammoniacal brine to form ammonium carbonate (NH4)2CO3
2NH3(g) + CO2 + H2O → (NH4)2CO3(aq)
Ammonium carbonate reacts with sodium chloride and form sodium bicarbonate (NaHCO3) and
ammonium chloride (NH4Cl).
(NH4)2CO3 (aq) + NaCl → NaHCO3(s) + NH4Cl (aq)
5.Filtration: The precipitate of sodium bicarbonate (NaHCO3) is separated from the solution by
filtration. It is used as baking soda.
6. Calcination: dry sodium bicarbonate (NaHCO3) is heated in rotatory funnel call calcinatory, to give
anhydrous sodium carbonate.
2NaHCO3(s) → Na2CO3(s) + CO2 (g) + H2O
7. Recovery of Ammonia: Ammonia is recovered from ammonia chloride solution and slaked lime.
Slaked lime is heated with ammonium chloride to form ammonia and calcium chloride which is the by
product.
2NH4Cl(s) + Ca (OH) 2(aq) → CaCl2 (aq) + 2NH3 (g) + 2H2O (l)

Q2.c. predict the by-products in the Solvay process.

Ans: By-products in the Solvay process:
the by-products of Solvay process is calcium chloride.
Q2.d. sketch the flow sheet diagram of the Solvay process.
Ans:

Q3.a. Enlist raw material used in the manufacture of urea?

Ans: Urea: Urea is an organic compound having a carbonyl (C═O) functional group attached to two –
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 87

NH2. . Urea is one of the most important nitrogenous fertilizers. Its chemical formula is NH2CONH2.
The formula shows that urea is composed of nitrogen, hydrogen. Carbon and oxygen.
Raw material used in the manufacture of urea material used in the manufacture of urea are
following.

• Ammonia (NH3)
• Carbon dioxide (CO2)
Ammonia (NH3): ammonia is prepared by Haber process. In this process, nitrogen and hydrogen react
when they are passed over iron catalyst at 4500C and 200 atmosphere pressure. It produces ammonia.
N2 (g) + 3H2 (g) → 2NH3 (g)Carbon dioxide: it can be prepared from natural gas (CH4).
CH4 (g) + H2O (g) → CO2 (g) + 4H2 (g)
Q3.b. What basic reactions would you use to support the manufacture of urea?
Ans: Basic reaction:
Manufacture of urea involves the following steps.
1. Reaction of Ammonia and carbon dioxide: ammonia and carbon dioxide are heated at 17o –
2000C and 100-200 atmospheric pressure to form ammonium carbamate.
2NH3 (g) + CO2 (g) → NH2COONH4
2.Urea formation: when ammonium carbamate is heated it decomposes and produce water and urea.
NH2COONH4 → NH2CONH + H2O
3. Evaporation and granulation of liquid: in this step, liquid urea is concentrated in vacuum
evaporators. It is sprayed from top of tower under pressure and hot current of air in introduced from
the bottom in opposite direction. It evaporates water from urea. It is rapidly cooled and sent to the
granules. This urea is stored to be marketed.
Q3.c. What is the advantage of recycling of untreated compound in manufacture of urea?
Ans: Advantages of Recycling: manufacture urea contain untreated ammonia and carbon dioxide and
ammonium carbamate. Ammonium carbamate is removed by reduction the pressure. When heating
ammonia and carbon dioxide is separated. The advantage of this process is that ammonia and carbon
dioxide can be recycle back to the process. Which increases urea yield.
Q3.d. Sketch the flow sheet diagram of urea manufacture process.

Q4.a.Define refining of petroleum. Describe the composition of petroleum?

Ans: Refining of petroleum:
the conversion of crude oil into useful products with different boiling range and d free from impurities
is called refining of petroleum.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 88

Composition of petroleum: petroleum is the mixture of various hydro carbons. It includes petroleum
gas such as methane, ethane, propane and butane, naphtha petrol which range from C4 – C1. Kerosene
oil ranges from C12 – C16, diesels oils from C14 – C25, lubricating oil C20 – C70 and residue which is
above C70.
Q4.b. What are the two theories about origin of petroleum?
Ans: There are two theories about origin of petroleum.
Inorganic origin: This theory was put forward by Russian chemist Mendeleev. He proposed that
steam reacted with metallic carbides at high temperature and pressure under the surface of the earth
produced petroleum. This theory did not gain popularity. According to this theory petroleum is
originated from non-living source.
Organic origin: according to this theory, the remain of plants and animals were buried under the soil
millions of year ago. These dead organic matter were converted into petroleum by the action of
bacteria under the influence of temperature and pressure of the earth. These deposits trapped between
the layers of nonporous rocks. The oil and gas thus formed could not come out and collected
underground. This theory gain popularity.
Q.4.c. write a detail note on fractional distillation of petroleum.
Ans: Fractional distillation: The type of distillation in which different fractions of petroleum are
separated according to difference in their boiling point is called Fractional distillation.
Basic principle of Fractional distillation: The fractions are separated according to difference in their
boiling point. The substances having less boiling points boils out first leaving behind others.
Fractional Column: Fractional distillation is carried out in fractionating column. It has different
compartment to collect different fractions.
Fractional distillation of petroleum: First of all crude oil is heated up to 4000C under high pressure
in a furnace. The heated mixture then passed through the fractional distillation column. The
fractionating g column is divided into different compartment. Each compartment has definite range of
temperature as hot vapours move up, they condense according to their boiling point into various
fractions. Compound with high boiling point will condense first near bottom, while those compounds
having low boiling points move to the top of column. Thus crude oil is separated into different
fractions.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 89

S.No Fraction Number of carbon BoilingPoint Uses

atoms per
molecule

1 Refinery Gas C1 – C4 Below 400C Methane (CH4)

coking, ethane
another gaseous fuel,
carbon-3 and carbon-
4 as portable energy
source and butane for
camping gas

2 Naphtha-petrol C4 – C12 400C - 1300C Naphtha used as a

(gasoline) solvent and important
chemical and as light
engine oil
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 90

3 Kerosene C12 – C16 1500C - 2000C Less volatile, less

(paraffin oil) flammable than
petrol, used for
domestic heating fuel
(paraffin), aircraft jet
fuel (kerosene)

4 Diesel Oils C14 – C225 2250C - 3000C Less volatile than

petrol, used as a fuel
in large vehicle such
as trucks, trains etc.

5 Lubricating oil C20 – C70 3000C - 4000C Viscous and used as

lubricating oil and
greases

6 Residue Above C70 Above 4000C Used on roads as it

(bitumen/ forms a thick, black,
Asphalt) tough and resistant
adhesive surface on
cooling, also used as a
roofing water
proofing material

Q5.a. write a detail note metallurgical operations.

Ans: Metallurgy: The art and science of making of making metals and alloys from their ores with
properties suitable for practical uses is called metallurgy. OR
The science that deals with the procedures used in extracting metals from their ores, purifying, alloying
metal sand creating useful objects from metal is called metallurgy.
Basic metallurgical operations: In metallurgy the ores are mined and subjected to various mechanical
and chemical processes. There is no single method for extracting metals from their ores, But certain
basic operation are required that is,
i. Concentration of ores
ii. Extraction of metal (roasting and reduction)
iii. Refining of metal.
1. Concentration of ore: the removal of useless rocky portion of the ore is called concentration of ore.
Explanation: Ore is impure metal containg large amount of sand and rocky material. These impurities
must be removed from the ore before the extraction of metal.
Crushing and grinding: Huge lumps of ores are broken down into small pieces and then reduced to
fine powder with the help of ball mill or stamp mill. This process is called pulverization.
Method used: there are mostly physical methods of concentration and also some chemical methods.
1. Hand picking: in this method the ores are concentrated to sufficient degree of purity by simple
picking it with hand and breaking the rock stones with hammer.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 91

2. Hydraulic washing:
Basis: This method is based on difference in densities of the ore and gangue.
Procedure: In this process, the ore particles are poured over a hydraulic classifier which is vibrating
inclined able with grooves and a jet of water is allowed to flow over it. The denser are settled in the
grooves while the lighter gangue particles are washed away.
Forth floatation: A separating method of the mineral particles of ore from the gangue that depends on
the wetting of the minerals pieces.
Function of forth floatation: It is a process for selectively separating hydrophobic materials from
hydrophilic. In this process the ore is wetted with water and pine oil. And the water insoluble
impurities float on the surface and thus separated from the ore.
Steps:
1. Floatation tank: concentration of copper ore is carried out in floatation tank.
2. Crushing and grinding: In this step the ore is reduced to fine powder through crushing and
grinding.
3. Froath formation: the powdered ore is suspended in water, soap or pine oil is added and a blast of
air is bubbled through the suspension to produce froth.
4. Particle of ore: the particle are wetted by oil and float at the top of the mixture in container from
which it is collected.
5. Concentrated Ore: the froth is washed with water and then filtered to obtain concentrated ore.
While undissolved particles settle down at the bottom.
ii. Extraction of metal (roasting and reduction)
See L.Q 1 (part b and c).
iii. Refining of metal.
See L.Q 1 part d.
Q5.b. Explain the process of smelting and Bessemerization with reference to copper extraction.
Ans: Smelting: It is the process in which the oxide ore in the fused state is reduced with reducing
agents such as coke to get the metal is called roasting.
Procedure: The roasted ore of copper is mixed with coke and sand and smelted into blast furnace.
During smelting iron sulphide (FeS) get oxidized to iron oxide (FeO). The iron oxide then react with
silica (SiO2) forming iron silicate (FeSiO3).
2FeS(s) + 3O2(g) → 2FeO(s) + 2SO2(g)
FeO(s) + SiO2(s) → FeSiO3
Cuprous sulphide (Cu2S) is also oxidizes and form copper oxide (Cu2O).
2Cu2S + 3O2 → 2Cu2O + 2SO2(g)
Cu2O then reacts with un-reacted FeS and form Cu2S and FeO.
Cu2O(s) + FeS(s) → Cu2S(s) FeO(s)
TheCu2Sand FeS is called matte and is removed through slag hole.
Bessemerization:
History: Bessemer process was invented by Henry Bessemer.
Bessemer converter: This process is carried out in a special kind of egg shaped or pear shaped
furnace.
This furnace is called Bessemer.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 92

Procedure: In Bessemerization matte is reacted with sand. Iron sulphide (FeS) oxidized to Iron oxide
(FeO). This iron oxide (FeO) reacts with sand (SiO2) forming (FeSiO3), slag which is float on the
surface.
2FeS + 3O2 → 2FeO + 2SO2
FeO + SiO2 → FeSiO3
Similarly Cuprous sulphide (Cu2S) is converted to cuprous oxide (Cu2O). this Cu2O reacts with Cu2S
to produce copper (Cu) in molten form and sulphur dioxide (SO2). This copper is known as blister
copper (95-97% pure).
2Cu2S + 3O2 → 2Cu2O + 2SO2
2Cu2O + Cu2S → 6Cu + SO2
Q.5.c. Enlist the different uses of urea.
Ans: Uses of urea:
it is a white crystalline organic compound. It is important due to the following usage.
1. Fertilizer: about 86% of urea is used as solid fertilizer.
2. Resins: Urea-formaldehyde resins are used as a poly-wood adhesive/glues.
3. Use as explosive: Urea can be used to make urea nitrate, which is highly explosive.
4. Chemical Industry: Urea is used as a raw material for manufacture of many important chemical
compounds like plastics, resins, and various adhesives etc.
5. Flame proofing agent: Urea is used as a flame proof in agent.
6. Cosmetics: it is used as an ingredient in hair conditioners, facial cleaners and lotions.
7. Repellent to Corrosion: It is used as an alternative to rock salt in the deicing roadways and
runways. It does not promote metal corrosion to extent that salt does.
8. Cigarette: It is also used as flavor enhancing additive for cigarette.
9. Medicinal uses: urea containing creams are used as tropical dermatological products to promote
rehydration of skin.

TOPIC WISE QUESTIONS

Q2. What is drilling of petroleum?
Ans: Drilling of petroleum: the process by which petroleum is taken out from the earth by the use of
various equipment is called drilling of petroleum.
Naturally: petroleum usually occurs at the depth of 500 feet of more. Crude oil is often associated
with natural gas which exerts pressure on the oil surface and drives it out through natural opening of
earth.
 https://web.facebook.com/TehkalsDotCom/
https://tehkals.com/ 93

Artificially: in case of artificial mining, mines are bored. If the natural gas is present with the
petroleum its pressure forces the petroleum to come out. If there is no natural gas then the air pressure
is applied to force the oil from the well.