LOYOLA INTERNATIONAL SCHOOLS

QATAR
Academic Session: 2024 -2025
Practice WORKSHEET

NAME: _________________________________ Roll No:______________________

CLASS: X Topics: Acid, base and salt

1. A compound X of sodium is used as an antacid and it decomposes on

strong heating.
(i) Name the compound X and give its chemical formula.
(ii) Write a balanced chemical equation to represent the decomposition of
X
(iii) Give one use of compound X besides an antacid.

Answer: (i) Compound ‘X’ is Sodium bicarbonate. Its chemical formula is

NaHCO3.
(ii) Decomposition reaction of ‘X’:

(iii) Besides the use of antacid, it is also used in fire extinguishers.

2. You are provided with 90ml of distilled water and 10 ml of concentrated

sulphuric acid to prepare dilute sulphuric acid.
(i) What is the correct way of preparing dilute sulphuric acid? Give reason.
(ii) What is this process called.
(iii) How will the concentration of H3O+ ions change on dilution?
Answer:
(i) Add 10 mL of concentrated sulphuric acid slowly to 90 mL of water with
constant stirring.
(ii) Dilution of acid is a highly exothermic process. If water is added to
concentrated sulphuric acid, heat generated causes the mixture to splash
leading to burns and the glass container can break.
(iii) Decreases per unit volume.
3. Observe the given figure and answer the questions that follow:

(i) Identify the gas X.

(ii) Write the chemical reaction involved.
(iii) Which type of chemical reaction is taking place?
Answer:
(i) The gas X is hydrogen gas (H2). This is because the reaction taking place
is between a metal and an acid, which typically produces hydrogen gas.
(ii) The chemical reaction involved is:
Metal + Acid → Salt + Hydrogen gas
For example, if the metal is zinc (Zn) and the acid is hydrochloric acid (HCl),
the reaction would be:
Zn + H2SO4 → ZnSO4 + H2
(iii) The type of chemical reaction taking place is a single displacement
reaction. This is because the metal is displacing the hydrogen from the acid.
4. You have four solutions A, B , C and D. The pH of solution A is 6, B is 9, C
is 12 and D is 7.
(i) Identify the most acidic and most basic solutions.
(ii) Arrange the above four solutions in the increasing order of H+ ion
concentration.
Given data:
 a. The pH of solution A is 6.
b. The pH of solution B is 9.
c. The pH of solution C is 12.
d. The pH of solution D is 7.
As we know that;
a. The pH value represents the nature of the solution.
b. If the pH is more than 7 implies that the solution is basic in nature.
c. If the pH is less than 7 implies that the solution is acidic in nature.
d. For neutral solutions, the pH value is 7.
e. The pH value can be calculated by the formula pH=-
logH+ where H+ is the concentration of hydronium ion H+.
From the given data we can say that;
a. Solution A is acidic in nature.
b. Solution B is basic in nature.
c. Solution C is basic in nature and it is more basic than solution B as its
pH is more than that of solution B.
d. Solution D is neutral in nature.
Hence, the increasing order of given solutions H+ ion concentration is
C< B< D< A
5. (i) Write the chemical formula of hydrated copper sulphate and
anhydrous copper sulphate
(ii) Write chemical names and formula of plaster of Paris and gypsum.
Answer: (i) Hydrated Copper sulphate⇒CuSO4.5H2O
Anhydrous Copper Sulphate⇒CuSO4
(ii) Plaster of paris- CaSO4.1/2H2O- Calcium sulphate semihydrate.
Gypsum- CaSO4.2H20
6. Mrs. Tomas uses a compound of sodium X to make pakoras crispy. It is a
mild non-corrosive basic salt, also used as an ingredient in antacids. It is
produced using sodium chloride as one of the raw materials.

(i) Identify the compound of sodium X . Is the pH value of X solution lower

than or higher than 7?

(ii) Write the chemical equation of preparation of X .

(iii) Write the chemical reaction involved when X is heated.
(iv) State the chemical properties on which the following uses of X are
based:
Answer:
(i) The compound 'X' is a constituent of baking powder. It is called baking
soda.
(ii) NaCl+H2O+CO2+NH3→NH4Cl+NaHCO3
(iii). Chemically, the compound is sodium hydrogen carbonate with the
formula NaHCO3. Upon heating, the compound 'X' will release carbon
dioxide gas.
2NaHCO3→Na2CO3(s)+H2O(l)+CO2(g)
(iv) It is a mild non-corrosive base.
When baking soda is heated or mixed with water, CO2 is produced which
causes bread and cake to raise making them soft and spongy.
7. (i) What are strong and weak acids?
(ii) In the following list of acids, separate strong acids from weak acids.
Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric
acid.
Answer: Strong acids are acids that completely ionize in water. Weak acids
are acids that only partially ionize in water.
Strong acids: Hydrochloric acid, nitric acid, sulphuric acid
Weak acids: Citric acid, acetic acid, formic acid
8. State reason for the following statements:
(i) Tap water conducts electricity whereas distilled water does not.
(ii) Dry hydrogen chloride gas does not turn blue litmus red whereas dil.
HCl does.
(iii) During summer season, a milkman usually adds a very small amount
of baking soda to fresh milk.
(iv) For dilution of acid, acid is added to water and not water into acid.
(v) Ammonia is a base but does not contain hydroxyl group.
Answer:

(i) Tap water contains ions that conduct electricity, distilled water does not
contain ions. Ions are the current carriers in liquids, hence distilled water
does not conduct electricity.

(ii) Dry HCl does not form ions but an aqueous solution of HCl furnishes H+
and Cl- ions, these ions carry electric currents.

(iii) Baking soda does not allow milk to change into curd by neutralizing
lactic acid formed with time. This delays the curdling of milk.

(iv) Adding water to acid is highly exothermic. If water is added to acid, the
acid may splash out and may cause accidents. Hence acids are added to
water with regular stirring.

(v) Ammonia dissolves in water and accept H+ from H2Omolecules to

release OH– ions in solution. Therefore, it is basic in nature.

9. (i) Discuss the role of pH in:

Digestive system, and Causes of tooth decay.

(ii) Give the constituents of baking powder.
(iii) Why does cake or bread swell on adding baking powder? Write
chemical equation.
(i) Role of pH in digestive system:

In the stomach, hydrochloric acid is secreted as food enters the stomach. It turns
the pH of the stomach between 1 and 3

. This pH is important for the activation of the enzyme pepsin, which helps in the
digestion of protein in food.
Cause of tooth decay:
• Tooth decay starts when the pH of acid formed in the mouth falls below
5.5 because then the acid becomes strong enough to attack the enamel
of our teeth and corrode it.
(ii) Baking powder containing sodium hydrogen carbonate and tartaric
acid.
(iii)It is due to carbon dioxide

10. Observe the given figure and answer the following questions:

(i) C02
(ii) C02 act as a fire extinguisher and hence it extinguishes burning candle.

(iii)
(iv) On passing excess C02, lime water becomes clear due to the formation
of soluble calcium bicarbonate.
11. Anhydrous copper sulphate (CuSO4) was dissolved in one beaker and
hydrated copper sulphate (CuSO4.5H2O) was dissolved in another beaker.
What heat changes do you expect in these beakers and why?
Answer:
When Anhydrous copper sulphate is dissolved in water it releases lot of
heat energy from the reaction thus the process is called exothermic
reaction
Whereas hydrated copper sulphate already has some moles of water, hence
less heat is emitted.
12. Metal compound A reacts with dilute Hydrochloric acid to produce
effervescence. The gas evolved extinguishes a burning candle. Write a
balanced chemical equation for the reaction if one of the compounds
formed is Calcium chloride.

Answer:

When a metal compound A on reacting with hydrochloric acid shows

effervescence which shows the evolution of carbon dioxide gas and it is
confirmed by putting off the candle flame.
So, metal compound A is a calcium carbonate which on reacting with HCl
gives calcium chloride and carbon dioxide as gas along with water.
CaCO3(s) + 2HCl(aq) → CaCl2(s) + CO2(g) + H2O(l)
13. A metal compound A reacts with dilute sulphuric acid to produce a gas
which extinguishes a burning candle. Identify the compound A and the gas
produced. Write a balanced chemical equation for the reaction if one of the
compounds formed in the reaction in sodium sulphate.
When sodium carbonate reacts with sulphuric acid, it produces carbon
dioxide gas with effervescence.
Carbon dioxide is used as fire extinguisher; hence it extinguishes a burning
candle.
Therefore, the metal compound A is sodium carbonate.
14. How does the enamel of the teeth undergo damage due to the eating of
chocolates and sweets? What should be done to prevent it.
Answer:
Tooth enamel is made of calcium phosphate. It does not dissolve in water
but it starts corroding when the pH in the mouth decreases to 5.5 or less.
When we eat chocolates, small pieces of these stick to our teeth. The
bacteria present in our teeth start decaying the food particles as a result of
which small amount of acid is produced. This acid, decreases the pH of the
mouth and results in the decaying of tooth enamel.
15. Name the gas which is usually produced when dil. sulphuric acid reacts
with a metal. Illustrate it with an example. How will you test the evolution
of this gas?
Answer:
Metals react with dil. sulphuric acid to give metal sulphates and hydrogen
gas.
For example,
Zn(s)+H2SO4(aq)→ZnSO4(aq)+H2↑
Test for hydrogen gas:
Take about 5 m1 of dilute sulphuric acid in a test tube and add a few pieces
of zinc granules to it. Hydrogen gas is evolved during this reaction. Now
bring a burning candle near the hydrogen gas-filled test tube. It will put off
with a pop sound

16. The soil in a field is highly acidic. List any two materials which can be
added to this soil to reduce its acidity. Give reason for your choice.
Answer:
If the soil in the field is highly acidic, then we need to add bases in the soil
the two bases which we use are
1: calcium hydroxide Ca(OH)2
2: calcium carbonate CaCO3
these bases have power to neutralize the excess acid in the field. the bases
neutralize the acids and thus makes the field safer from acidic medium. if
acidic medium is being in the field then it reduces its fertility.
17. List the important products of the Chlor- alkali process. Write one
important use of each.
Answer:
The important products formed in this process are sodium hydroxide,
chlorine, and hydrogen gas.
2NaCl+2H2O⟶2NaOH+Cl2+H2
An electric current is passed through the brine to form H2 at the cathode
and Cl2 at the anode, leaving a solution of sodium hydroxide.

Uses of sodium hydroxide:

1. It is used in the manufacturing of paper.

2. It is used for making soaps and detergents.

Uses of chlorine:

1. It is used in the production of bleaching powder.

2. It is used in the production of hydrochloric acid (HCl).

Uses of Hydrogen gas:

1. It is used as fuel for rockets.

2. It is used in the hydrogenation of oils to obtain vegetable ghee.

18. How is washing soda prepared from sodium carbonate? Give its
chemical equation. State the type of this salt. Name the type of hardness of
water which can be removed by it?

19. Complete the following table:

Preparation of Plaster of Paris:

Uses of plaster of Paris:
(i) It is used as a fire proofing material.
(ii) it is used in hospitals for setting fractured bones in the right position to
ensure correct healing.
Preparation of bleaching powder:

Uses of bleaching powder:

Bleaching powder used in bleaching cotton, wood pulp, clothes.
Oxidising agent used in chemical industries.
Disinfectant to kill germs in drinking water.
20. Account for the following
(i) State the relation between hydrogen ion concentration of an aqueous
solution and its pH.
(ii) An aqueous solution has a pH value of 7. Is this solution acidic, basic
and neutral?
(iii) Which has a higher pH value, 1M HCl or 1 M NaOH solution?
Answer:
(i) There is a direct relation between hydrogen ion concentration of an
aqueous solution and its pH.
The formula will be:
pH = -log [H+]
(ii) The aqueous solution having a pH value ranging between 0-7 is known
to be acidic in nature, whereas it will be basic if the value will range
between7-14.
However, for the pH value equal to 7, the aqueous solution is denoted as
neutral in nature.
(iii) 1 M NaOH solution.
21. Blue litmus solution is added to two test tubes A and B containing dilute
HCl and NaOH solution respectively. In which test tube a colour change will
be observed? State the colour change and give its reason.
Answer:
Blue litmus in dilute HCl (Test tube A)
• HCl is acidic in nature.
• The colour of blue litmus changes from blue to red due to dilute acid.
Blue litmus in NaOH (Test tube B)
• The colour of the blue litmus will not change due to the basic
solution.
So, the colour changes will be observed in test tube A. The colour is
blue to red.
22. Identify the basic salt from the following salts:

Answer: (i)
23. (i)Identify the acid and the base whose combination forms the common
salt. Write the formula and chemical name of this salt. Name the source
from which it is obtained?
(ii) What is rock salt? Mention its colour and the reason it is due to,
(iii) What happens when an electric current is passed through brine? Write
the chemical equation for it.
Answer:
(i) HCl is acid and NaOH is base whose combination forms the common salt.
Its formula is NaCl (Sodium chloride). It is obtained from sea water.
(ii) Rock salt is the common name for the mineral “halite”. Its chemical
formula is NaCl. It may be white or light blue or yellow depending upon
impurities present in it.
(iii) When electricity is passed through brine it decomposes to form sodium
hydroxide along with the evolution of chlorine gas at anode and hydrogen
gas at cathode. Sodium hydroxide solution is also formed near the cathode.

24. Identify the acid and base for ammonium chloride salt. Write the
nature(acidic/basic/neutral) and pH value of this salt.
Answer:
HCl, NH4OH=>NH4OH+HCl → NH4Cl+H2O
Nature of salt-acidic as it is formed by neutralisation of a strong acid and
weak base. Its pH value will be less than 7 (pH range 1-6)
25. What happen when Zinc reacts with HCl or NaOH?
Write the chemical equation and name of the salt produced in each case.
Answer:
(i) When zinc (Zn) reacts with dilute hydrochloric acid (HCl) it results in
the production of zinc chloride (ZnCl2) and hydrogen gas(H2)
Zn (s)+ 2HCl(l) →ZnCl2(s) + H2 (g)
(ii) When Zn metal is added to NaOH, it results in the formation of Sodium
zincate (Na2ZnO2) salt along with Hydrogen gas.

26. (i) What is water of crystallisation?

(ii) With the help of equations, state what happens when
(a) baking soda is heated during cooking?
(b) gypsum is heated at 373k?
Answer:
(i) The number of water molecules present in one formula unit of a salt is
known as the water of crystallization.
For example, in hydrated Copper sulphate (CuSO4·5H2O), 5 water
molecules are present.
So, the water of crystallization is 5 in this hydrated species.
(ii) (a) Sodium bicarbonate (baking soda) decomposes on heating to form
sodium carbonate, carbon dioxide and water.
The chemical reaction involved is:
2NaHCO3→Na2CO3+CO2+H2O

(b) When gypsum is heated at ,

CaSO4.2H2O ------- > CaSO4.1/2H2O (Plaster of Paris) + 1 1/2 H2O

27. Give reason for the following:

(i) Only one half of water molecules is shown in the formula of plaster of
Paris.
(ii) Sodium hydrogen carbonate is used as an antacid.
(iii) On strong heating, blue coloured copper sulphate crystals turn white.
Answer:
(i) Only one half of water molecule is shown in the formula of Plaster of
Paris because 2 formula units of CaSO4 /Calcium sulphate share 1 molecule
of water of crystallization.

(ii) Sodium hydrogen carbonate is used as an antacid because of the

alkaline nature it reacts with the excess acid in our stomach and thus
neutralizes it and gives relief to the stomach.

(iii) On strong heating, blue coloured copper sulphate crystals turn white,
which is shown by the following reaction -

CuSO4 .5H2O (Blue) ---------> CuSO4 (white) + 5H2O

Due to loss of water of crystallization, white color is obtained

28. (i) Draw a labelled diagram to show the preparation of hydrogen

chloride gas in laboratory.
(ii) Test the gas evolved first with dry and then with wet litmus paper.
(iii) State the reason of exhibiting acidic character by dry HCl gas/ HCl
solution.
Answer:
(i) The labelled diagram shows the preparation of hydrogen chloride gas in
the laboratory:

(ii) The colour of the litmus paper is changed by the hydrogen ions. Dry HCl
gas does not contain H+ ions. It is only in the aqueous solution that an acid
dissociates to give ions. Since in this case, neither HCl is in the aqueous form
nor the litmus paper is wet, therefore, the colour of the litmus paper does
not change.

(iii) Amongst dry HCl gas and HCl solution, HCl solution will show acidic
properties. This is because dry gas does not show any effect on the pH paper
or the litmus paper as it is not composed of H+ ions which are an essential
component of an acid.

29. Define water of crystallisation. Give the chemical formula for two
compounds as examples. How can it be proved that the water of
crystallisation makes a difference in the state and colour of the
compounds?
Answer:

Water of crystallization is the fixed number of water molecules present in

one formula unit of a salt

Examples CuSO4 .5H2O

Na2CO3.10 H2O

It be proved that the water of crystallisation makes a difference in the state

and colour of the compounds by Heating a few crystals of hydrated copper
sulphate (blue colour) in a dry boiling tube. Water droplets are seen in the
boiling tub.

Colour obtained: The colour of copper sulphate changes to white

State: The blue crystal changes to white powder

30. A cloth strip dipped in onion juice is used for testing a liquid X. The
liquid X change its odour. Which type of an indicator is onion juice?
The liquid X turn blue litmus red. List the observations the liquid X will
show on reacting with the following;
(a) Zinc granules
(b) Solid sodium carbonate
Write the chemical equations for the reaction involved.
Onion juice is an olfactory indicator. Olfactory indicators give one type of
odour in acidic medium and a different odour in basic medium. As the
liquid ‘X’ turns blue litmus red, hence it is an acidic solution.
(a) Acids react with active metals such as zinc, magnesium etc. and evolve
hydrogen gas, for example,

Zn(s) +dil.H2SO4(aq) → ZnSO4+ H2(g)

(b) Acids react with metal carbonates to give carbon dioxide with brisk
effervescence.
For example, Na2CO3 + H2SO4 → Na2SO4 + CO2 + H2O

31. The table below shows the colour of universal paper (UI) paper at
different pH values.
Answer: (i) Since universal indicator paper turns purple in oven cleaner
solution, we can infer that the pH of the oven cleaner solution is around 11-
12, as indicated by the purple color on the table.
(ii) The substance in the oven cleaner solution that turns UI paper purple is
likely a strong base, such as sodium hydroxide (NaOH), commonly found in
oven cleaners for its effective cleaning properties.
(iii) If UI paper turns yellowish-green in milk, it suggests that the pH of
milk is slightly acidic, around pH 6.
(iv) When the milk turns orange upon re-testing with UI paper after being
left outside for five days, it indicates that the milk has become acidic, likely
due to bacterial fermentation, which produces acidic by-products. This
change in pH from slightly acidic to acidic suggests that the milk has
spoiled.
32. Observe the given figure and answer the following questions:

(i) Which gas is produced by the reaction of zinc and dil. Sulphuric acid?
(ii) How will you test for the presence of the gas produced?
(iii) Name the salt produced when zinc metal reacts with sodium hydroxide
solution.
(iv) Can all bases react with active metals?
Answer:
(i) Zinc react with dil. sulphuric acid to give Zinc sulphates and hydrogen
gas. For example,
Zn(s)+H2SO4(aq)→ZnSO4(aq)+H2↑

(ii) Take about 5 m1 of dilute sulphuric acid in a test tube and add a few
pieces of zinc granules to it. Hydrogen gas is evolved during this reaction.
Now bring a burning candle near the hydrogen gas-filled test tube. It will
put off with a pop sound.
(iii) Zinc reacts with NaOH to form sodium zincate with the evolution of
hydrogen gas.
2NaOH(aq)+Zn(s) Δ⟶Na2ZnO2(aq) +H2(g)
(iv) Some metal reacts with a base to form salts and hydrogen (H2) gas.
Most metals do not react with bases but zinc (Zn) metal does because it is
amphoteric. That is, it reacts with acids as well as bases.
33. Study the table related to colour change with indicators and answer the
questions that follow.

(i) Name the solution which is acidic.

(ii) Arrange the given solutions increasing order of their pH value.
(iii) What is the name of solution P and Q?
(iv) When solution P is added to the china rose indicator, what is the colour
of solution P?
Answer:
(i) Q and R solutions are acidic. P- basic in nature.
(ii) R, Q, P
(iii) P- Milk of magnesia Mg (OH)2, Q-citric acid
(iv) P- basic solution, China rose gives green colour to the basic solution.
34. You are given a white solid which is calcium carbonate CaCO3

(i) What happens to the white solid after heating?

(ii) What will you observe in the lime water during the heating process?
(iii) Write the reaction involved.
(i) Heating of calcium carbonate results in formation of calcium oxide and
carbon dioxide. The reaction involved is:
CaCO3(s) heat−−→ CaO(s)+CO2(g)
(ii) When Carbon dioxide is passed through Lime water or Calcium
Hydroxide, it turns milky due to the formation of the Precipitate of the
insoluble milky Calcium Carbonate.
(iii) CO2+Ca(OH)2→CaCO3↓+H₂O.
35. A student takes three beaker A, B, C filled with aqueous solutions of
glucose, alcohol and hydrochloric acid respectively as shown in the
following figures.

A B C
(i) State your observation in terms of glowing of bulb when the switch is
on.
(ii) Justify your observation by giving reason in each case.
 (iii)Mentioned the change noticed with appropriate reason if the content of
beaker B is replaced by sodium hydroxide solution
Answer:
(i) Bulb A and B do not glow but bulb C glows.

(ii) Glucose and alcohol solutions do not conduct electricity as they do not
have ions.-Dil. HCl Contains, ions so the flow of current.
(iii) After replacement, bulb glows in B as NaOH solution contains ions
(Na+ and OH- ions).
36. The graph shows how the pH of the soil in a farmer’s field changed over
a period of time.

(i) At which point A, B, C or D did the farmer apply lime to the field.
(ii) What is the importance of pH in our daily life?
(iii) Give two examples showing importance of neutralisation in our daily
life.
Answer:
(i) Acidic substances range from 0 to 7 on the pH scale.

• The substance is said to be neutral at 7 pH.

• Substances are classified as basic between the pH scale of 7 and 14.
• Lime is often regarded as a strong base that produces alkaline (high pH)
solutions.
• As a result, when it is added to the soil, the soil should become more basic.
• The farmer should have applied lime to the field at point B.

(ii) The pH of the soil is an important factor in the growth of crops and
other plants. The ideal pH for the growth of shrubs and crops ranges from
6.5 to 7.3
In the human body, all the physiological reactions take place at the pH of 7-
7.8. pH is very important for our digestive system

The pH of the soil is an important factor in the growth of crops and other
plants. The ideal pH for the growth of shrubs and crops ranges from 6.5 to
7.3

(iii) Milk of magnesia, which is a base, is given as antacid in the case of

indigestion, to neutralize the excess acid produced in the stomach.

Mg(OH)2+2HCl⟶MgCl2+2H2O

• The ant sting can be painful as it has formic acid. We can neutralise this
acid effect and relieve the pain caused by the sting by using moist baking
soda which is basic in nature.

37. During electrolysis of brine, a gas G is liberated at anode. When this gas
G is passed through slaked lime, a compound C is formed, which is used for
disinfecting drinking water.
(i) Write formula of G and C
(ii) State the chemical equation involved.
(iii) What is common name of compound C? Give its chemical name.
Answer:
(i) The formula of ‘G’ and ‘C’ are,
G = Cl2
C = CaOCl2
(ii) The chemical equation involved is given below:
Ca(OH)2+Cl2→CaOCl2+H2O
(iii) The common name of compound C is Bleaching Powder. Its chemical
name is Calcium Oxychloride.
38. A liquid has a pH less than 7 which represents an acidic solution.
(i) State the nature of solution, if its pH increases from 7 to 14.
(ii) Mention the ion whose concentration increases with the increase in pH
value.
(iii) Suggest a method that is generally used for measuring pH value.
Answer:
(i) Since, there is increase in the strength of alkali, so the nature of solution
will be basic.
(ii) Hydroxide ion or hydroxyl ion or OH- ion.
(iii) A paper impregnated with the universal indicator is generally used to
measure the pH of a solution.
39. (i) What is Plaster of Paris?
(ii) How is plaster of Paris prepared?
(iii) Write equation of the reaction involve.
(iv) What happens when water is added to plaster of paris?
(v) Write an equation to show the reaction between plaster of paris and
water.

(i) Plaster of Paris is calcium sulphate hemihydrate. Its chemical formula

is: CaSO4.1/2H2O.

(ii) It is prepared by heating gypsum to a temperature of 1000C. It loses 3/4th of

its water of crystallisation and forms plaster of Paris.

(iii)2CaSO4.2H2O→(heated at 393K)→2(CaSO4).1/2H2O+1 1/2H2O

Gypsum Plaster of Paris Water

(iv)

40. Baking soda is used in small amounts of making bread and cakes. It help
to make these soft and spongy. An aqueous solution of baking soda turns
red litmus blue. It is also used in soda acid fire extinguisher. Use this
information to answer the following questions.
(i) Write the equation for the reaction between baking soda and acid.
(ii) How does it help in extinguishing fire?
(iii) What is the reaction involved when it is heated?
(iv) Is the pH value of baking soda solution lower than or higher than 7?
Answer:
(i) Baking soda reacts with the acidic ingredients of bread and cake to form
carbon dioxide gas which makes the foodstuff to rise and thus makes it soft
and spongy.

(ii) Soda acid fire extinguishers contain a mixture of sulphuric acid and
baking soda. They react to release carbon dioxide which forms a layer over
the burning substance and cuts the supply of oxygen of the fire.

(iii) NaHCO3+H2SO4→Na2SO4+2H2O+2CO2

(iv) The pH of baking soda solution is greater than 7 since, it is a salt of a

strong base, NaOH and a weak acid, H2CO3.
41. A girl met with an accident and her leg got fractured. She went to an
orthopaedical for treatment. On examination the doctor mixed a white
powder in water and applied it to her leg along with the cotton and gauze.
After a while, it turned into white, solid, hard mass. The doctor said that it
would support her fractured bone and help it to join the right position.

Answer:
(i) The chemical name and formula of the white coloured powder which is used
by doctors for supporting fractured bones is:
White powder- Plaster of paris
Chemical name of white powder- Calcium sulphate hemihydrate
Formula - CaSO4.1/2H2O
White hard solid mass- gypsum
Chemical name: Calcium sulphate dihydrate

The plaster of paris should be stored in a moisture-proof container because it

absorbs moisture (water) from the atmosphere easily and turns into a hard
substance (gypsum).

CaSO4.1/2 H2O+11/2H2O→CaSO4.2H2O

Plaster of paris Gypsum

(iii) When this white powder is mixed with water a hard-solid mass is obtained.
The balanced chemical equation for the change is
CaSO4.12H2O+1/2H2O→CaSO4.2H2O

CaSO4.1/2 H2O CaSO4.2H2O

Plaster of paris Gypsum

42. (i) Why does bee sting cause pain and irritation?
(ii) Rubbing of baking soda on the sting area gives relief. How?
Answer:
(i) When a bee stings a person, it injects an acidic liquid into the skin which
causes pain and irritation. The name of the chemical substance
is methanoic acid or formic acid.
(ii) If the bee stings a person, then rubbing a mild base like baking soda
solution on the stung area gives relief. Being a base, baking soda neutralizes
the acidic liquid injected by the bee sting and cancels its effect.
43. Explain why hydrochloric acid is a strong acid and acetic acid, a week
acid. How it can be verified?
HCl is completely ionised in aqueous solution whereas acetic acid is
partially ionised in aqueous solution. HCl gives dark red colour with pH
paper whereas CH3COOH gives orange colour.
44. Give suitable reason for the following statements:
(i) We feel burning sensation in the stomach when we overeat.
(ii) The crystal of washing soda change to white powder on exposure to air.
Answer:
(i) When we overeat excess of acid is produced in the stomach Which
causes burning sensation.
(ii) Washing soda is sodium carbonate decahydrate which when exposed to
air loses 10 molecules of water and changes to White powder.
45. To. a solution of sodium hydroxide in a test tube, two drops of
phenolphthalein are added.
(i) State the colour change observed.
(ii) If dil HCl is added dropwise to the solution, what will be the colour
change?
(iii) On adding few drops of NaOH solution to the above mixture the colour
of the solution reappears. Why?
Answer:
On adding phenolphthalein to NaOH solution, the colour becomes pink.
(ii) On adding dilute HCl solution dropwise to the same test tube, the pink
colour disappears and the solution again becomes colourless.
(iii) On again adding NaOH to the above mixture, pink colour reappears
because the medium becomes basic again.
46. Write one point of difference between each of the following:
(i) A hydrated salt and an anhydrous salt.
(ii) Washing soda and soda ash.
(iii) Baking soda and baking powder.
Answer:
(i) Hydrated salt is a salt with water as water of crystallisation whereas
Anhydrous salt is the salt which gives away its water of crystallisation.
(ii) Washing soda is sodium carbonate having ten molecules of water
crystallisation (Na2CO3.10H2O) and hence anhydrous, whereas soda ash is
sodium carbonate (Na2CO3).
(iii) Baking soda is sodium bicarbonate (NaHCO3) whereas baking powder
is a mixture of baking soda (NaHCO3) and tartaric acid (C4H6O6).
47. A compound ‘X’ on electrolysis in an aqueous solution produces a
strong base. ‘Y’ along with two gases ‘A’ and ‘B’. ‘B’ is used in the
manufacture of bleaching powder. Identify X, Y, A, and B. Write chemical
equations.
Answer:
we know that common salt, i.e., NaCl is used for the manufacture of sodium
hydroxide, i.e., NaOH, and this process is called the chloro-alkali process.
The chemical equation of this process is-
2NaCl(aq)+2H2O(l)⟶2NaOH+Cl2(g)+H2(g)

X=sodium chloride y=sodium hydroxide A=hydrogen gas B=Chlorine gas.

The active ingredient in bleaching powder is calcium

hypochlorite, Ca(OCl)2, and so gas "b" must be chlorine since chlorine is
reacted with calcium hydroxide to make calcium hypochlorite and calcium
chloride.

48. Give two important uses of washing soda and baking soda.
Answer:

Uses of Washing Soda:

(i) It is used for removing the permanent hardness of the water.

(ii) It is used in glass, soap, and paper industries.

Uses of Baking Soda:

(i) It is used in soda-acid fire extinguishers.

(ii) It is used in making baking powder. Baking powder is a mixture of

baking soda and a mild edible acid called tartaric acid. When baking
powder is heated or mixed in water, it releases that makes cakes or
bread fluffy.

49.What happens to the crystals of washing soda when exposed to air?

Answer:
When exposed to air, sodium carbonate decahydrate (Na2CO3.10H2O) or
washing soda crystal slowly loses its water of crystallisation and gets
converted into white powder.
Na2CO3.10H2O→Na2CO3.H2O+9H2O
The phenomenon exhibited by washing soda is called efflorescence.
50. Plaster of Paris should be stored in a moisture-proof container. Explain
why?
Answer:
Plaster of Paris is a white powder and on mixing with water, it changes to
gypsum giving a hard solid mass.

Hence, it should be stored in a moisture-proof container