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In acidic medium, how many moles of KMnO4 are required to oxidise 1 mole of Fe2+ ions to Fe3+ ions?

1. 1/5 moles of KMnO4
2. 5/3 moles of KMnO4
3. 2/5 moles of KMnO4
4. 5/2 moles of KMnO4

Correct answer: 1/5 moles of KMnO4

Solution

One MnO4- accepts 5 electrons while each Fe2+ donates 1, so 1 mole of KMnO4 oxidises 5 moles of Fe2+; hence 1 mole Fe2+ needs 1/5 mole KMnO4.

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