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One mole of an equimolar mixture of ferric oxalate (Fe2(C2O4)3) and ferrous oxalate (FeC2O4) is completely oxidised by acidified KMnO4 solution. How many moles of KMnO4 are required?
- 0.6 mole
- 0.9 mole
- 0.3 mole
- 1.8 mole
Correct answer: 0.6 mole
Solution
Equimolar mixture: 0.5 mol ferric oxalate [Fe2(C2O4)3] and 0.5 mol ferrous oxalate [FeC2O4]. Ferric oxalate: Fe3+ (no oxidation of Fe), 3 oxalate ions each losing 2e- = 6e- per formula unit; 0.5 mol * 6 = 3 mol e-. Ferrous oxalate: Fe2+ -> Fe3+ (1e- per Fe), 1 oxalate losing 2e-; total 3e- per formula unit; 0.5 mol * 3 = 1.5 mol e-. Total electrons = 4.5 mol. KMnO4 gains 5e- per mol in acid. Moles KMnO4 = 4.5/5 = 0.9 mol.
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