Reduction of potassium permanganate (manganate (VII)) with sulphite at different pH with equations

KMnO4 - potassium permanganate or manganate (VII) is a well-known oxidizing agent.

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In acidic conditions purple potassium permanganate is reduced to colorless manganese (II) ions.

If pH is high reduction goes not to to completion as there is not enough H+ ions to remove oxides from the manganate (VII) complex. Reduction goes to form MnO2 precipitate in neutral conditions and green unstable MnO2- (manganate (VI)) solution in alkaline conditions.

The list of ions and complexes containing Mn at different oxidation states:

MnO4- oxidation state +7 purple
MnO42- oxidation state +6 green, disproportionates reduction at pH 14
MnO2 oxidation state +4 brown precipitate reduction at pH 7
Mn2+ oxidation state +2 colorless reduction at pH 1