Question

For sulfurous acid (h2so3, a diprotic acid) write the equilibrium dissociation reactions and the corresponding expressions for the equilibrium constants

Answer 1

Since the acid is diprotic, there are two equilibrium dissociation reactions for it. Consequently, there will also be two expression for equilibrium constants, Ka₁ and Ka₂.

First reaction:
H₂SO₃ ⇄ 2H⁺ + HSO₃²⁻          ------>     Ka₁ = [H⁺][HSO₃²⁻]/[H₂SO₃]

Second reaction:
HSO₃²⁻ ⇆ H⁺ + SO₃²⁻             ------>     Ka₂ = [H⁺][SO₃²⁻]/[HSO₃²⁻]