Q1(c). Solvent levelling

Answer in brief

Ammonia is a stronger proton acceptor than water, so proton transfer from HF is much more complete in liquid ammonia.

Key points

• In water: HF + H₂O ⇌ H₃O⁺ + F⁻. The equilibrium gives only partial ionisation of HF.
• In liquid ammonia: HF + NH₃ → NH₄⁺ + F⁻. The stronger basic solvent accepts the proton readily.
• Acids stronger than NH₄⁺ in liquid ammonia are levelled to NH₄⁺, the characteristic solvent acid. Acid strength must therefore be specified with the solvent.