Chemical reaction: HCN(aq) + H₂O(l) ⇄ CN⁻(aq) + H₃O⁺(aq).
Ka = [CN⁻] · [H₃O⁺] / [HCN].
[HCN] is equilibrium concentration of hydrocyanic acid.
hydrocyanic acid is weakly acidic and partially ionizes in water solution and give the cyanide anion (CN⁻).
The salts of the cyanide anion are called cyanides.