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How many moles of KMnO4 are required to oxidize 1 mol of Cu2S in acidic medium, given the products are Mn²+, Cu²+, and SO2?
- 0.8
- 0.4
- 1.2
- 1.6
Correct answer: 1.6
Solution
In Cu2S: Cu is +1 (two atoms) and S is -2. Products: Cu²+ means each Cu loses 1 electron (2 Cu atoms = 2 electrons total), SO2 means S is +4 (change from -2 to +4 = 6 electrons). Total electrons lost by Cu2S = 2 + 6 = 8 per mole. KMnO4 in acid: Mn changes from +7 to +2, gaining 5 electrons per mole. By electron equivalence: moles KMnO4 * 5 = 1 * 8. Moles KMnO4 = 8/5 = 1.6.
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