In the reaction MnO4- + 8 H+ + 5 Fe2+ → Mn2+ + 5 Fe3+ + 4 H2O, which species is oxidized?

• A. Fe2+ is oxidized to Fe3+
• B. MnO4- is oxidized to Mn2+
• C. H+ is oxidized to H2
• D. Fe3+ is oxidized to Fe4+

Answer: (A)

Oxidation state changes show who loses electrons. In this reaction, iron starts as Fe2+ (iron(II)) and ends as Fe3+ (iron(III)), which means each iron atom loses one electron. That loss of electrons makes Fe2+ the species being oxidized. The permanganate ion, MnO4−, instead gains electrons and is reduced to Mn2+ (manganese goes from +7 to +2), which is why MnO4− acts as the oxidizing agent. The protons (H+) simply balance the equation and end up in water; their oxidation state stays +1, so they aren’t oxidized. There’s no process here that would raise Fe3+ to Fe4+. Therefore, iron(II) is the species that is oxidized.