Sunday, July 3, 2022

Why does a temporary color appear in KMnO4 titration with oxalic acid?

The titration of potassium permanganate (KMnO4) against oxalic acid (C2H2O4) is a redox titration.

As the reaction intensifies, the color of the solution will fade. It will start out dark purple, as the acid is added and the reaction is heated (at room temperature, it is quite slow), the permanganate ions will be converted to manganese 2+ cations in solution.

These are almost colorless (a very pale pink) while oxalic acid (C2H2O4) is converted to carbon dioxide (CO2) and water (H2O). For complete oxidation to occur, the reaction must occur in an acidic solution, which is usually accomplished by adding dilute sulfuric acid (H2SO4) to the process. 

Throughout the reaction, if the solution becomes neutral, some brown manganese (IV) oxide MnO2 will also form (which will precipitate out).


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