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Balance the atoms being oxidized or reduced.Balance oxidation numbers by adding electrons.Balance charge by adding H+ (acidic solutions) or OH- (basic solutions).Balance H atoms by adding H2O.
Balancing Redox Reactions
Write the half reactions.Balance each half reaction.Combine the half reactions to eliminate the electrons from the overall reaction.
Example
Fe2+(aq) + MnO4-(aq) Fe3+(aq) + Mn2+(aq) (acidic solution)
1. Write the half reactions:
Fe2+(aq) Fe3+(aq) (oxidation)
MnO4-(aq) Mn2+(aq) (reduction)
2. Balance each half reaction:
Fe2+(aq) Fe3+(aq) + e-
MnO4-(aq) + 8H+(aq) + 5e- Mn2+(aq) + 4H2O
3. Combine the half reactions to give the overall reaction:
5Fe2+(aq) 5Fe3+(aq) + 5e-
MnO4-(aq) + 8H+(aq) + 5e- Mn2+(aq) + 4H2O
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5Fe2+(aq) + MnO4-(aq) + 8H+(aq) 5Fe3+(aq) + Mn2+(aq) + 4H2O
Try balancing the lead-acid battery reaction:
Pb(s) + PbO2 (s) + SO42-(aq) PbSO4(s)
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