The amount of charge in F (Faraday) required to obtain one mole of iron from Fe₃ O₄ is ___________. (Nearest Integer)

Solution

Chemistry ma’am · 4 steps

Find how many electrons each Fe gains: in Fe₃O₄ iron sits at an average of +8/3, not +2 or +3.

1. Oxidation state. Oxygen is -2, so four O atoms give -8. Three Fe atoms must balance it with +8, so the average oxidation state of Fe is +8/3.
2. Electrons per formula. Taking all three Fe from a total of +8 down to 0 needs 8 electrons. So one mole of Fe₃O₄ needs 8 F and gives 3 mol of Fe.

   Fe₃O₄ + 8e⁻ → 3Fe + 4O²⁻

3. Per mole of Fe. Charge for one mole of Fe = 8/3 F = 2.67 F.
4. So. 2.67 F rounds to 3.

The common slip: 8. Stopping at the charge for one mole of Fe₃O₄ gives 8, but that produces 3 mol of Fe. Divide by 3 to get the charge for one mole.

The idea to keep. Faradays needed per mole of metal equals the drop in its oxidation state. For mixed oxides like Fe₃O₄, use the average oxidation state.

Answer from the NTA final answer key. Solution by PrepWiser.