Explain why

(a) anhydrous HCl is a poor conductor while aqueous HCl is an excellent conductor.

(b) when the stopper of a bottle full of hydrogen chloride gas is opened there are fumes in the air.

(c) a solution of hydrogen chloride in water turns blue litmus red and conducts electricity, while a solution of the same gas in toluene

(i) has no effect on litmus, and

(ii) does not conduct electricity.

(d) dry hydrogen chloride gas does not affect a dry strip of blue litmus paper, but it turns red in the presence of a drop of water.

(e) dilute hydrochloric acid cannot be concentrated by boiling beyond 22.2%.

(a) Anhydrous HCl is a gas and does not contain any ions, hence it is a poor conductor of electricity. On the other hand, aqueous HCl (HCl dissolved in water) forms ions in solution, and thus becomes an excellent conductor of electricity.

HCl + H₂O ⟶ H₃O⁺ + Cl^-

(b) When hydrogen chloride gas is exposed to air, it gives white fumes, due to the formation of hydrochloric acid on dissolving in atmospheric water vapour.

(c) A solution of hydrogen chloride in water gives ions,

HCl + H₂O ⟶ H₃O⁺ + Cl^-

These ions are responsible for conducting electricity and turning blue litmus red, due to the presence of hydronium [H₃O⁺] ions which make aqueous solution of HCl acidic in nature.

Toluene is an organic solvent and HCl is a covalent compound. A solution of HCl in toluene contains only molecules and not ions due to which it does not conduct electricity. The absence of hydronium [H₃O⁺] ions make the solution neutral and it does not effect litmus paper.

(d) Dry hydrogen chloride gas does not contain any ions. Due to the absence of hydronium [H₃O⁺] ions, it is neutral and does not affect a dry strip of blue litmus paper. On the other hand, in the presence of a drop of water, HCl dissolves in it and dissociates into hydronium [H₃O⁺] ions and chloride ions [Cl^-]

HCl + H₂O ⟶ H₃O⁺ + Cl^-

The presence of hydronium [H₃O⁺] ions makes the aqueous solution acidic and blue litmus turns red.

(e) Hydrochloric acid forms a constant boiling mixture at 110°C, 22.2% by weight. On boiling further, the mixture evolves out the vapours of both acid and water in the same proportion as in the liquid.

Hence, dilute HCl cannot be concentrated beyond 22.2% by boiling.