Question

how does KMnO4 act as a self indicator

Answer 1

 KMnO4 solutions are dark purple. When used as a titrant, as soon as the endpoint is reached and the KMnO4- is in excess, the solution has a permanent pink hue (provided that the solution is initially colorless). Thus KMnO4 acts as its own indicator.

Answer 2

Potassium Permanganate is an oxidizing agent, which is of deep violet colour. When used in redox titration, it get reduced into brown coloured Mn2+ ion(In acidic media) at end point and colour change at end point can be detected easily. Since detecting end point is the role of indicator, later is not required in Permanganate titration also.
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