Q1(h). Acidity of concentrated HF

Answer in brief

At higher HF concentration, association stabilises fluoride-containing conjugate-base species such as HF₂⁻, promoting proton release.

Key points

• HF alone is only partly ionised in dilute water because the H–F bond is strong and dissociation must be considered with solvation.
• Fluoride associates strongly with another HF molecule: F⁻ + HF ⇌ HF₂⁻. This removes free fluoride from the simple dissociation equilibrium.
• Combining the equilibria gives 2HF + H₂O ⇌ H₃O⁺ + HF₂⁻.