Answer:

A reaction which has an equal number of atoms of all the elements on both sides of the chemical equation is called a balanced chemical equation.

The law of conservation of mass states that mass can neither be created nor destroyed. Hence, in a chemical reaction, the total mass of reactants should be equal to the total mass of the products. This means that the total number of atoms of each element should be equal on both sides of a chemical equation. Hence, it is for this reason that chemical equations should be balanced.

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

Explanation: When dilute hydrochloric acid (HCl) is added to iron filings (Fe), a chemical reaction takes place. Hydrogen gas (H₂) and iron chloride (FeCl₂) are produced. This is a typical reaction of a metal with an acid.

Chemical Reaction:

Fe (s) + 2 HCl (aq) → FeCl2 (aq) + H2 (g)

Answer: (d) The given reaction is an example of a displacement reaction.

Explanation: In the reaction, aluminum (Al) displaces iron (Fe) from iron oxide (Fe₂O₃), which is characteristic of a displacement reaction. Displacement reactions occur when one element displaces another from a compound.

Chemical Reaction:

Fe2O3 (s) + 2 Al (s) → Al2O3 (s) + 2 Fe (s)

2PbO (s) + C (s) → 2Pb (s) + CO2 (g)

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

Statements:

1. (a) Lead is getting reduced.
2. (b) Carbon dioxide is getting oxidised.
3. (c) Carbon is getting oxidised.
4. (d) Lead oxide is getting reduced.

Select the correct option:

1. (i) (a) and (b)
2. (ii) (a) and (c)
3. (iii) (a), (b) and (c)
4. (iv) All

(i) Oxidation and Reduction in the Reaction

Answer: In this reaction, sodium (Na) is oxidized as it gains oxygen, and oxygen (O₂) is reduced by gaining electrons.

Chemical Reaction:

2 Na (s) + O2 (g) → 2 Na2O (s)

(ii) Oxidation and Reduction in the Reaction

Answer: In this reaction, copper oxide (CuO) is reduced to copper (Cu), while hydrogen (H₂) gets oxidized to form water (H₂O).

Chemical Reaction:

CuO (s) + H2 (g) → Cu (s) + H2O (l)

Answer:

Sodium carbonate reacts with calcium chloride to form calcium carbonate and sodium chloride. In this reaction, sodium carbonate and calcium chloride exchange ions to form two new compounds. Hence, it is a double displacement reaction.

Chemical Reaction:

Na2CO3 (aq) + CaCl2 (aq) → CaCO3 (s) + 2 NaCl (aq)

Explanation of the Chemical Reaction:

When an iron nail is placed in a copper sulfate solution, a chemical displacement reaction occurs. During this reaction, iron displaces copper from the copper sulfate solution.

Displacement Reaction:

The iron nail reacts with the copper sulfate (CuSO₄) to form iron sulfate (FeSO₄) and free copper metal. This reaction is represented by the following equation:

Fe + CuSO₄ → FeSO₄ + Cu

As a result, the blue colour of the copper sulfate solution fades, and a green colour appears due to the formation of iron sulfate, which is green in colour.

Answer:

Water (H₂O) contains two parts hydrogen and one part oxygen. Therefore, the amount of hydrogen and oxygen produced during electrolysis of water is in a 2:1 ratio. During electrolysis, since hydrogen goes to one test tube and oxygen goes to another, the amount of gas collected in one of the test tubes is double of the amount collected in the other.

The gas collected in the test tube containing the larger amount is hydrogen gas (H₂).

Answer:

i) The substance ‘X’ is calcium oxide. Its chemical formula is CaO.

ii) Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime) as shown below:

CaO + H2O → Ca(OH)2