Chemical Reactions and Equations

NCERT Exercise solution

Question: 1: Which of the statements about the reaction below are incorrect?

2PbO (s) + C (s) → 2Pb (s) + CO₂(g)

1. Lead is getting reduced
2. Carbon dioxide is getting oxidized
3. Carbon is getting oxidized
4. Lead oxide is getting reduced

1. (a) and (b)
2. (a) and (c)
3. (a), (b) and (c)
4. all

Answer: (i) (a) and (b)

Explanation: Here, lead oxide loses oxygen and hence reduced. Carbon gains oxygen and hence oxidized. And not lead is getting reduced. Carbon dioxide is not getting oxidized.

Question: 2:

The above reaction is an example of a

1. Combination reaction
2. Double displacement reaction
3. Decomposition reaction
4. Displacement reaction

Answer: (d) Displacement reaction

Explanation: In the given reaction Iron is displaced by aluminium and hence, the given reaction is an example of Displacement Reaction.

Question: 3: What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

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.

Answer: (a) Hydrogen gas and iron chloride are produced

Explanation:

When hydrochloric acid is added to iron fillings, hydrogen gas and iron chloride are formed.

Question: 4: What is a balanced chemical equation? Why should chemical equations be balanced?

Answer: Chemical reactions in which number of atoms of each of the elements present in both sides, i.e. in reactant and product sides, is equal are called a balanced chemical equation.

Law of Conservation of Mass says that mass can neither be created nor be destroyed. This means that total mass of reactants must be equal to the total mass of products in a chemical reaction.

Hence, in order to satisfy the Law of Conservation of Mass, a chemical reaction should be balanced.

Question: 5: Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.

Answer:

(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

Answer:

(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.

Answer:

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Answer:

Question: 6. Balance the following chemical equations.

(a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O

(b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O

(c) NaCl + AgNO₃ → AgCl + NaNO₃

(d) BaCl₂ + H₂SO₄ →BaSO₄ + HCl

Answer: