2Na2SO3 + H2O2 → 2NaHSO3 + H2O

Description:

Sodium sulphite (Na2SO3) and hydrogen peroxide (H2O2) react to form sodium hydrogen sulphite (NaHSO3) and water (H2O). The reaction is an example of a redox reaction, where sodium sulphite is oxidized and hydrogen peroxide is reduced.

Mechanism:

The reaction proceeds through a free radical chain mechanism. The first step is the homolytic cleavage of the O-O bond in hydrogen peroxide to form two hydroxyl radicals (·OH).

H2O2 → 2·OH

The hydroxyl radicals then react with sodium sulphite to form sodium hydrogen sulphite and a sulphite radical (·SO3-).

2·OH + Na2SO3 → 2NaHSO3 + ·SO3-

The sulphite radical can then react with another molecule of hydrogen peroxide to regenerate a hydroxyl radical and form a persulphate radical (S2O82-).

·SO3- + H2O2 → ·OH + S2O82-

The persulphate radical can then react with another molecule of sodium sulphite to form sodium hydrogen sulphite and a sulphate radical (·SO4-).

S2O82- + Na2SO3 → 2NaHSO3 + ·SO4-

The sulphate radical can then react with another molecule of hydrogen peroxide to regenerate a hydroxyl radical and form a hydrogen sulphate radical (HSO4·).

·SO4- + H2O2 → ·OH + HSO4·

The hydrogen sulphate radical can then react with another molecule of sodium sulphite to form sodium hydrogen sulphite and a water molecule.

HSO4· + Na2SO3 → NaHSO3 + H2O

Overall Reaction:

The overall reaction is the sum of the individual steps:

2Na2SO3 + H2O2 → 2NaHSO3 + H2O