In the half-reaction MnO4- + 8 H+ + 5 e− → Mn2+ + 4 H2O, which species is reduced, and is this the reduction or oxidation half-reaction?

• A. Mn2+ is reduced to MnO4-; this is the oxidation half-reaction.
• B. MnO4- is reduced to MnO2; oxidation half-reaction.
• C. MnO4- is reduced to Mn2+; this is the reduction half-reaction.
• D. MnO4- is oxidized to Mn2+; oxidation half-reaction.

Answer: (C)

At the heart of redox chemistry is the gain or loss of electrons, which changes oxidation states. Here, manganese goes from +7 in MnO4− to +2 in Mn2+. That’s a decrease in oxidation state by five, meaning a gain of electrons. The species that undergoes this gain is the permanganate ion, MnO4−, which is reduced to Mn2+. Because electrons appear on the left side of the equation, this is a reduction half-reaction. The given equation also aligns with permanganate being reduced in acidic solution to Mn2+.