For the ion Fe^{3+}, how many moles of electrons are required to completely reduce one mole of Fe^{3+} to Fe(s) during electrolysis?

• A. 2 moles
• B. 3 moles
• C. 6 moles
• D. 1 mole

Answer: (B)

Verified step by step guidance

1. Identify the oxidation states of the species involved. Fe^{3+} has an oxidation state of +3, and Fe(s) (solid iron) has an oxidation state of 0.
2. Determine the change in oxidation number per iron ion when it is reduced from Fe^{3+} to Fe(s). This change is from +3 to 0, which means a gain of 3 electrons per Fe ion.
3. Recall that during reduction, electrons are gained. Therefore, each mole of Fe^{3+} requires 3 moles of electrons to be completely reduced to Fe(s).
4. Write the half-reaction for the reduction process: \(\mathrm{Fe^{3+} + 3e^- \rightarrow Fe(s)}\).
5. Conclude that to reduce one mole of Fe^{3+} ions, 3 moles of electrons are needed, based on the stoichiometry of the half-reaction.