It’s because KMnO4 acts as a self-indicator, the indicator is not required in the titration of permanganometry. A self-indicator is a chemical compound that itself indicates the endpoint of the titration.
KMnO4 is an oxidizing agent that turns purple in solution and becomes colorless when reduced to Mn2+ ions. Potassium permanganate is used in redox titrations as a titrant against a solution or analyte that contains Fe2+ ions.
It is a deep purple color in an environment with a basic pH level. When introduced to an acidic medium, KMnO4 turns colorless. This is due to the reduction of KMnO4 and the transition of Mn (VII) to an Mn (II) state. For this reason, we don't need to use an indicator.
Its primary purpose is to provide a visual signal for the viewer so that they can determine when the reaction is complete. Additionally, potassium permanganate is a very potent indicator.
Particularly if we perform the titration in reverse (Example: the acid in the burette and permanganate in the conical flask) such that the permanganate changes from pink to colorless, it's very simple to detect the color change.
For example, when KMnO4 is in slight excess, a solution of sodium oxalate (Na2C2O4) and potassium permanganate (KMnO4) turns from colorless to pink.
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