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In acidic medium, potassium dichromate acts as an oxidising agent according to the half-reaction: Cr2O7²- + 14H⁺ + 6e⁻ -> 2Cr³+ + 7H2O. If the molar mass of K2Cr2O7 is M, what is its equivalent weight?
- M
- M/2
- M/3
- M/6
Correct answer: M/6
Solution
From the half-reaction, one mole of Cr2O7²- gains 6 electrons (each Cr goes from +6 to +3, and there are 2 Cr atoms: 2*3 = 6 electrons). One formula unit of K2Cr2O7 contains one Cr2O7²- unit, so n-factor = 6. Equivalent weight = Molar mass / n-factor = M/6.
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