CLASS 10TH
Chemical Reactions and Equations
In-text questions set 1
1. Why should a magnesium ribbon be cleaned before burning in the air?
Solution:
Because magnesium metal combines with ambient oxygen to generate magnesium
oxide (MgO) layer, a very stable chemical, magnesium ribbon should be cleaned before
burning in the air. Hence, the ribbon must be cleaned by removing the coating of MgO
in order to stop more reactions with oxygen.
2. Write a balanced equation for the following chemical reactions.
i) Hydrogen + Chloride —-> Hydrogen chloride
ii) Barium chloride + Aluminium sulphate —-> Barium sulphate + Aluminium
chloride
iii) Sodium + Water —-> Sodium hydroxide + Hydrogen
Solution:
i) H2 + Cl2 → 2HCl
ii) 3BaCl2 + Al2(SO4)3 →3BaSO4 + 2AlCl3
iii) 2Na + 2H2O → 2NaOH + H2
3. Write a balanced chemical equation with state symbols for the following
reactions
i) Solutions of Barium chloride and Sodium sulphate in water react to give
insoluble Barium sulphate and solution of Sodium chloride.
ii) Sodium hydroxide solution in water reacts with the hydrochloric acid
solution to produce Sodium chloride solution and water.
Solution:
i) BaCl2 + Na2SO4 → BaSO4 + 2NaCl
ii) NaOH + HCl → NaCl + H2O
In-text questions set 2
1. A solution of a substance, ‘X,’ is used for whitewashing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Solution:
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i) The substance ‘X’ which is used in whitewashing is quick lime or Calcium Oxide
and its formula is CaO.
ii) CaO + H2O → Ca(OH)2
2. Why is the amount of gas collected in one of the test tubes in Activity 1.7
double the amount collected in the other? Name this gas.
Solution:
In activity 1.7, water hydrolyses to release H2 and O2 gas, which results in twice as
much gas being collected in one test tube as in the other. Here, two molecules of
hydrogen and one molecule of oxygen gas are released during electrolysis; as a result,
twice as much hydrogen would be recovered as oxygen.
In-text questions set 3
1. Why does the colour of copper sulphate solution change when an iron nail is
dipped in it?
Solution:
Because iron is more reactive than copper, iron displaces copper from the copper
sulphate solution when an iron nail is dipped in it. As a result, the copper sulphate
solution's hue changes. The response is
Fe + CuSO4 → FeSO4 + Cu
2. Give an example of a double displacement reaction other than the one given in
Activity 1.10.
Solution:
A double displacement reaction occurs between sodium chloride (NaCl) and
silver nitrate (AgNO3). Because white silver chloride precipitate forms during the
process, positive and negative ions exchange places. The following is a chemical
reaction diagram.
–
Ag+ + NO3 + Na+ + Cl– → AgCl + Na+ + NO3 –
3. Identify the substances that are oxidised and that are reduced in the
following equation.
i) 4Na(s) + O2(g) → 2Na2O(s)
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ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
Solution:
The Sodium (Na) in the first equation is getting oxidized with the addition of Oxygen
(O2), and the Copper (Cu) in the second equation is reduced due to the addition of
Hydrogen (H2).
Exercise Questions
1. Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2(g)
(a) Lead is getting reduced
(b) Carbon Dioxide is getting oxidised
(c) Carbon is getting oxidised
(d) Lead oxide is getting reduced
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all the above
Solution:
(i) (a) and (b)
Explanation: (a) Because Oxygen is being removed and (b) Because the removed
oxygen from Lead is added to the elemental Carbon.
2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
1. Combination reaction
2. Double displacement reaction
3. Decomposition reaction
4. Displacement reaction
Solution:
The answer is 4. Displacement reaction.
Aluminium oxide is created when oxygen from ferrous oxide is transferred to aluminium
metal. Aluminium is a more reactive metal than Fe in this reaction. Al will so remove Fe
from its oxide. One element displaces another in this kind of chemical reaction, known
as a displacement reaction. In this instance, more reactive metal replaces less reactive
metal. It is referred to as a single displacement reaction since it is a one-time
displacement.
3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the
correct answer.
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1. Hydrogen gas and Iron chloride are produced.
2. Chlorine gas and Iron hydroxide are produced.
3. No reaction takes place.
4. Iron salt and water are produced.
Solution:
1. Hydrogen gas and Iron chloride are produced.
Explanation: The Chlorine from Hydrogen chloride is displaced by the Iron fillings to
undergo the following reaction.
2HCl + Fe → FeCl2 + H2
4. What is a balanced chemical equation? Why should a chemical equation be
balanced?
Solution:
When the number of distinct atoms on the reactant and product sides of the equation is
equal, the equation is said to be balanced. Chemical equations must be balanced in
order for the reaction to follow the Law of Conservation of Mass. There is no set
procedure for balancing the chemical equation; it is just a matter of trial and error.
5. Translate the following statements into chemical equations and balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in the air to give water and sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give Aluminium
chloride and aprecipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and Hydrogen
gas.
Solution:
(a) Unbalanced: H2 + N2 → NH3
Balanced: 3H2 + N2 → 2NH3
(b) Unbalanced: H2S + O2 → H2 O + SO2
Balanced: 2H2S + 3O2 → 2H2 O + 2SO2
(c) Unbalanced: BaCl2 + Al2(SO4)3 → AlCl3 + BaSO4
Balanced: 3BaCl2 + Al2(SO4)3 → 2AlCl 3 + 3BaSO4
(d) Unbalanced: K + H2O → KOH + H2
Balanced: 2K + 2H2O → 2KOH + H2
6. Balance the following chemical equations.
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(a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Solution:
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2 O
(b) 2NaOH + H2 SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
7. Write the balanced chemical equation for the following reactions.
1. Calcium hydroxide + Carbon dioxide —-> Calcium carbonate + Water
2. Zinc + Silver nitrate —-> Zinc nitrate + Silver
3. Aluminium + Copper chloride —-> Aluminium chloride + Copper
4. Barium chloride + Potassium sulphate —-> Barium sulphate + Potassium
chloride Solution:
2Ca(OH)2 + 2CO2 → 2CaCO3 + 2H2O
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
2Al + 3CuCl2 → 2AlCl3 + 3Cu
BaCl2 + K2SO4 → BaSO4 + 2KCl
8. Write a balanced chemical equation for the following and identify the type of
reaction of each case.
KBr + BaI2 → KI + BaBr2
ZnCO3 → ZnO + CO2
H2 + Cl → HCl
Mg + HCl → MgCl2 + H2
Solution:
2KBr + BaI2 → 2KI + BaBr2 (Double Displacement Reaction)
ZnCO3 → ZnO + CO2 (Decomposition Reaction)
H2 + Cl → 2HCl (Combination Reaction)
Mg + 2HCl → MgCl2 + H2 (Displacement Reaction)
9. What is meant by exothermic and endothermic reactions? Give examples.
Solution:
When energy is taken up from the environment in the form of heat (such as during
photosynthesis, ice melting, or evaporation), an endothermic process takes place. On
the other hand, an exothermic reaction is one in which energy is released into the
environment from the system (Examples: nuclear fission and fusion, concrete setting,
explosions).
10. Why is respiration considered to be an exothermic reaction?
Solution:
Energy is necessary for life to survive. Food is the source of this energy for us. During
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the digestive process, food molecules are broken down into simpler molecules, such as
glucose. When these materials interact with the oxygen found in our body's cells,
carbon dioxide, water, and a little quantity of energy are produced (the respiration
process). As the energy used to sustain our body temperature takes the form of heat,
respiration is regarded as an exothermic reaction. The response that is occurring is:
C6H12O6 + 6O2 → 6CO2 + 6H2 O + Energy
11. Why are decomposition reactions called the opposite of Combination
reactions? Write equations for decomposition reactions.
Solution:
The decomposition process is defined as the splitting of bigger molecules into two or
more smaller molecules, whereas the combination reaction is defined as the reaction of
two or more molecules to generate a larger molecule. This basically clarifies how the
decomposition process differs from the combination reaction.
Since the heat from the environment or heat-induced breaks the bonds of the bigger
molecule, the breakdown mechanism is usually endothermic. Several instances of
breakdown reactions include
ZnCO3 → ZnO + CO2
CaCO3 + Energy → CaO + CO2
2HgO → 2Hg + O2
12. Write one equation each for decomposition reactions in which energy is
supplied in the form of heat, light or electricity.
Solution:
(a) Thermal decomposition reaction (Thermolysis)
Decomposition of potassium chlorate: When heated strongly, potassium chlorate
decomposes into potassium chloride and oxygen. This reaction is used for the
preparation of oxygen.
2KClO3 + Heat → 2KCl + 3O2
(b) Electrolytic decomposition reaction (Electrolysis)
Decomposition of sodium chloride: On passing electricity through molten sodium
chloride, it decomposes into sodium and chlorine.
(c) Photodecomposition reaction (Photolysis)
Decomposition of hydrogen peroxide: In the presence of light, hydrogen peroxide
decomposes into water and oxygen.
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13. What is the difference between displacement and double displacement
reactions? Write relevant equations for the above.
Solution:
A double displacement reaction occurs when two compounds exchange ions, while a
displacement reaction occurs when a more reactive substance removes a less
reactive one from its salt solution.
A displacement reaction involves only one displacement between the molecules,
whereas a double displacement reaction involves two displacements, as the name
implies.
Example:
Displacement reaction
Mg + 2HCl → MgCl2 + H2
Double displacement reaction
2KBr + BaI2 → 2KI + BaBr2
14. In the refining of Silver, the recovery of silver from Silver nitrate solution
involves displacement reaction by Copper metal. Write down the reaction
involved.
Solution:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
15. What do you mean by a precipitation reaction? Explain by giving examples.
Solution:
Ions are exchanged between the compounds in a double displacement reaction that
occurs when two solutions containing soluble salts are mixed. One of these
compounds sinks to the bottom of the container as it solidifies and becomes insoluble
in water. The precipitate is the name given to this solid, and the precipitation reaction is
the name given to the corresponding reaction. Several instances of precipitation
reactions include
CdSO4(aq) + K2S(aq) → CdS(s) + K2SO4(aq)
2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)
16. Explain the following in terms of the gain of oxygen with two examples each.
(a) Oxidation
(b) Reduction
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Solution:
(a) In a chemical reaction, when the oxygen is added to the element to form its
respective oxide it is the element being oxidised. Example:
4Na(s) + O2(g) → 2Na2O(s)
H2S + O2 → H2 O + SO2
(b) In a chemical reaction, when the oxygen is removed from the compound, then it is
said to be reduced. Example:
CuO(s) + H2(g) → Cu(s) + H2O(l)
2HgO → 2Hg + O2
17. A shiny brown coloured element ‘X’ on heating in the air becomes black in
colour. Name the element ‘X’ and the black-coloured compound formed.
Solution:
The shiny brown-coloured element is Copper metal (Cu). When the metal is heated in
air, it reacts with atmospheric oxygen to form copper oxide. Hence, the black-coloured
compound is copper oxide.
2Cu(s) + O2(g) → 2CuO(s)
18) Why do we apply paint on iron articles?
Solution:
Paint is used on iron objects to stop them from rusting. If the metal surface is not
coated, it will come into contact with airborne oxygen and, in the event of moisture,
iron(III) oxide. However, painting shields the surface from air and moisture, which
stops rusting.
19) Oil and Fat containing food items are flushed with Nitrogen. Why?
Solution:
The major goal of flushing nitrogen into food packages containing fat and/or oil is to stop
rancidity, which happens when the fat or oil combines with oxygen to release an off-
putting taste and smell. Consequently, an unreactive environment is produced by
flushing nitrogen, preventing rancidity.
20) Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Solution:
(A) The process of corrosion involves oxidising refined metal with air to create oxides,
which are more stable compounds. When the metal corrodes, it steadily deteriorates.
One example of corrosion in which iron is transformed into iron oxide is the rusting of
iron. Every year, millions of dollars are spent to keep monuments like bridges from
rusting.
(B) The situation that results in an unpleasant taste and smell due to the aerial
oxidation of the fat and oil in the food item. Food stored in the refrigerator slows down
its rancidity because the low temperature inhibits the oxidation process.
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