The following reaction takes place when potassium permanganate reacts with oxalic acid. The deep purple colour of KMnO₄ disappears as MnSO₄ forms. This concept is used in redox titration

5H₂C₂O₄ + 2KMnO₄ +3H₂SO₄ ——>2MnSO₄ + 8H₂O + K₂SO₄ +10CO₂ ^{(deep purple) (Colourless)}