In acid medium H+ ions and water are added to half-reactions to balance the overall reaction. For example, when manganese reacts with sodium bismuthate.

Unbalanced reaction: Mn2+(aq) + NaBiO3(s) ? Bi3+(aq) + MnO4–(aq)
Oxidation: 4 H2O(l) + Mn2+(aq) ? MnO4–(aq) + 8 H+(aq) + 5 e–
Reduction: 2 e– + 6 H+(aq) + BiO3–(s) ? Bi3+(aq) + 3 H2O(l)

Finally, the reaction is balanced by multiplying the number of electrons from the reduction half reaction to oxidation half reaction and vice versa and adding both half reactions, thus solving the equation.

8 H2O(l) + 2 Mn2+(aq) ? 2 MnO4–(aq) + 16 H+(aq) + 10 e–
10 e– + 30 H+(aq) + 5 BiO3–(s) ? 5 Bi3+(aq) + 15 H2O(l)

Reaction balanced:

14 H+(aq) + 2 Mn2+(aq) + 5 NaBiO3(s) ? 7 H2O(l) + 2 MnO4–(aq) + 5 Bi3+(aq) + 5 Na+(aq)

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