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How many moles of acidified KMnO4 are needed to oxidise one mole of sulphite ion (SO3²-) to sulphate ion (SO4²-)?
- 2/5
- 3/5
- 4/5
- 1
Correct answer: 2/5
Solution
Balancing electrons: 2 mol MnO4- (10 e- gained) oxidises 5 mol SO3²- (10 e- lost), so 1 mol SO3²- needs 2/5 mol KMnO4.
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