Question 1

Why is acidified KMnO4 called a self-indicator?

Accepted Answer

Potassium permanganate has an intense purple colour. During the reaction it is reduced to nearly colourless Mn2+, but the first slight excess of titrant produces a pale-pink colour that remains briefly, revealing the endpoint without a separate indicator.

Question 2

What is the correct endpoint colour in a KMnO4 titration?

Accepted Answer

The endpoint is the first permanent pale-pink or faint pink colour, commonly stated to persist for 30 seconds. It should not be described as a red or deep-pink endpoint.

Question 3

Why is acidified oxalic acid warmed to about 70–80 °C before titration?

Accepted Answer

Moderate warming helps the oxalic acid reaction proceed suitably with permanganate. The flask contains acidified oxalic acid, while acidified KMnO4 is placed in the burette.

Question 4

What is the stoichiometric ratio between KMnO4 and Fe2+ in acidic medium?

Accepted Answer

The balanced ionic equation is MnO4− + 5Fe2+ + 8H+ → Mn2+ + 5Fe3+ + 4H2O. Therefore one mole of permanganate reacts with five moles of Fe2+.

Question 5

Why are n-factors used in permanganate titrations?

Accepted Answer

A reaction can combine unequal numbers of oxidant and reductant moles because their n-factors differ. In the stated acidic reactions, KMnO4 has n = 5, oxalic acid has n = 2, and Fe2+ has n = 1, so equivalent calculations use n-factor multiplied by moles.

Permanganate Titration in 3D — Oxalic Acid and Mohr's Salt

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