Acidified KMnO4 can be decolourised by Fe2+(orC2O2−4,SO2etc.)
Potassium permanganate is a strong oxidizing agent and it oxidizes these ions/molecules and itself is reduced.. This results in decolourization.
Ferrous ion is oxidized to ferric ion and oxalate ion is oxidized to carbon dioxide.
Hence, the cation and the anion in the salt ferrous oxalate decolourizes permanganate ion in acidic medium.
2MnO−4+5C2O2−4+16H+→2Mn2++10CO2+8H2O
MnO−4+5Fe2++8H+→5Fe3++Mn2++4H2O
SO2 can decolourises MnO−4/H+ solution and turn Cr2O2−7/H+ solution green.
Sulphur dioxide reduces potassium permanganate to Mn(Ii). ion. Hence, potassium permanganate is decolourized.