An acidified solution of 0.1000mol dm⁻³ ammonium vanadate (25.00cm³) was reduced by SO₂ and, after boiling off excess reductant, the blue solution remaining was found to require addition of 25.00 cm³ 0.0200 mol dm⁻³ KMnO₄ to give a pink colour to the solution. Another 25.00 cm³ portion of the vanadate solution was shaken with Zn amalgam and then immediately poured into excess of the ammonium vanadate solution; on titration of the resulting solution with the KMnO₄ solution, 74.5 cm³ of the latter was required. Deduce what happened in these experiments.