Titration using potassium manganate (VII) and acidified ethanedioate solution. At the start of the titration, the colour of the potassium manganate (VII) solution takes some time to disappear as Mn7+ ions are reduced to Mn2+ ions. The colour of the solution then disappears quickly as the Mn2+ ions increase in concentration and catalyse the reaction. Here, at the end of the titration, there are no more ethanedioate ions left to react, so the remaining potassium manganate(VII) solution gives the mixture a pink colour. See images C030/3774 and C030/3776 for the earlier parts of the reaction.