Question

What is the action of KMnO₄ in an acidic medium on the following?

Na₂SO₃

Write a balanced equation.

Answer 1

When KMnO₄ reacts with Na₂SO₃ in an acidic medium, the sulphite ion is oxidised to sulphate, and permanganate is reduced to Mn²⁺, with disappearance of the pink colour.

\[\ce{2KMnO4 + 5Na2SO3 + 3H2SO4 -> 2MnSO4 + K2SO4 + 3H2O}\]

or,

\[\ce{2MnO^-_4 + 5SO^{2-}_3 + 6H+ -> 2Mn^{2+} + 5SO^{2-}_4 + 3H2O}\]