Question

Assertion (A): Diluted hydrochloric acid cannot be concentrated beyond 22.2% (by weight) by distillation.

Reason (R): Mixture of water and hydrochloric acid forms constant boiling mixture.

Options

• If both A and R are true, and R is the correct explanation of A.

• If both A and R are true, but R is not the correct explanation of A.

• If A is true, but R is false.

• If both A and R are false.

Answer 1

If both A and R are true, and R is the correct explanation of A.

Explanation:

At 22.2% HCl by weight, the mixture forms a constant-boiling mixture known as an azeotrope. When this mixture boils at 110°C, both water and hydrogen chloride gas distil out in the same ratio, with no change in concentration. Therefore, simple distillation cannot concentrate the acid any further because the vapours have the same composition as the liquid.