Balance the redox reaction in acidic solution: MnO4- + Fe2+ → Mn2+ + Fe3+. Which is the balanced equation in acidic solution?

• A. MnO4- + 5 Fe2+ + 8 H+ → Mn2+ + 5 Fe3+ + 4 H2O
• B. MnO4- + 5 Fe3+ + 8 H+ → Mn2+ + 5 Fe2+ + 4 H2O
• C. MnO4- + 5 Fe2+ → MnO2 + 5 Fe3+ + H2O
• D. MnO4- + Fe2+ + 8 H+ → Mn2+ + Fe3+ + H2O2

Answer: (A)

Balancing redox in acidic solution uses half-reactions. Permanganate, MnO4−, is reduced from Mn in +7 to Mn2+, so it must gain 5 electrons. Iron(II) is oxidized from Fe2+ to Fe3+, giving up 1 electron per ion, so 5 Fe2+ are needed to supply those 5 electrons. In acidic solution, balance oxygen with water and hydrogen with H+. The MnO4− reduction half-reaction becomes MnO4− + 8 H+ + 5 e− → Mn2+ + 4 H2O. The Fe2+ oxidation half-reaction is Fe2+ → Fe3+ + e−, and multiplying by 5 gives 5 Fe2+ → 5 Fe3+ + 5 e−. Combining these cancels the electrons and yields the balanced equation: MnO4− + 5 Fe2+ + 8 H+ → Mn2+ + 5 Fe3+ + 4 H2O. This matches the standard result for this redox couple in acidic solution.