Core Reactions: Balancing Redox Reactions in Acidic Medium

Core Reactions: Balancing Redox Equations

Slide 15 of 29

A Note on the two Oxidizing Agents

Have a look at the balanced half equations for the reduction of dichromate(VI) and managate(VII) ions:

Cr2O72- + 14H+ + 6e- ® 2Cr3+ + 7H2O

MnO42- + 8H+ + 5e- ® Mn2+ + 4H2O

When the reducing agent is one without any oxygen (as in the example considered, Cl-) notice that the number of hydrogen ions and water molecules in the balanced half-equations are dictated by the number of oxygen in the oxidizing agent.

And therefore, the number of hydrogen ions and water in the final balanced equation is a multiple of that.

Cr2O72- (aq) + 14H+ (aq) + 6Cl- (aq) ® 3Cl2 (g) + 2Cr3+ (aq) + 7H2O (l)

–1´ that in the reduction half-equation.

2MnO42- (aq) + 10Cl- (aq) + 16H+ (aq) ® 2Mn2+ (aq) + 5Cl2 (aq) + 8H2O (l)

–2´ that in the balanced reduction half-equation.

Not only that, the balanced half equations appear on page 19 of the Data Booklet.