Balance the redox reaction MnO4- + C2O4^2- → Mn2+ + CO2 in acidic solution. Which is the overall balanced equation?

• A. 4 MnO4- + 8 H+ + 3 C2O4^2- → 4 Mn2+ + 4 H2O + 6 CO2
• B. MnO4- + 2 H+ + C2O4^2- → Mn2+ + CO2
• C. 2 MnO4- + 16 H+ + 5 C2O4^2- → 2 Mn2+ + 8 H2O + 10 CO2
• D. MnO4- + C2O4^2- → Mn2+ + CO2

Answer: (C)

Balancing redox reactions in acidic solution uses the half-reaction method. The permanganate ion is reduced to Mn2+ in acid, while oxalate is oxidized to CO2.

First half-reaction (reduction in acid):

MnO4- + 8 H+ + 5 e- → Mn2+ + 4 H2O

Second half-reaction (oxidation):

C2O4^2- → 2 CO2 + 2 e-

To ensure electron transfer is balanced, multiply the reduction half-reaction by 2 and the oxidation half-reaction by 5. That gives:

2 MnO4- + 16 H+ + 10 e- → 2 Mn2+ + 8 H2O

5 C2O4^2- → 10 CO2 + 10 e-

Add them and cancel the electrons:

2 MnO4- + 16 H+ + 5 C2O4^2- → 2 Mn2+ + 8 H2O + 10 CO2

This satisfies mass and charge balance in acidic solution. The numbers also reflect the need for the acid to balance the MnO4- reduction and the electron transfer with oxalate oxidation.