Question

Dry ammonia has no action on litmus paper but a solution of ammonia in water turns red litmus paper blue. Why is it so?

Answer 1

In dry state Ammonia contains no hydroxyl ions. On dissolving in water, it forms NH₄OH which dissociates to give NH₄ ⁺ and OH^-ions. Thus solution becomes basic and turns red litmus paper blue.

NH₃ (g) + H₂O (l) ---------------> NH₄OH (aq)

NH₄OH (aq) --------------> NH₄⁺ (aq) + OH^- (aq)