2. Balancing Redox rx

3. Steps to balancing in an acidic solution. 1.Write half-reactions without including electrons. 2.Balance the number of all atoms except oxygen and hydrogen. 3.Balance oxygen atoms by adding water molecules. 4.Balance hydrogen atoms by adding H +

4. 5.Balance charge by adding electrons. 6.Equalize electrons in the half-reactions by multiplication. 7.Combine the two half reactions. 8.Check to see that atoms and charges balance.

5. Cu + NO 3 - → Cu 2+ + NO Balance the reaction: Write the two half reactions –Cu → Cu 2+ –NO 3 - → NO

6. –Cu → Cu 2+ There is no oxygen or hydrogen in this reaction, so leave it alone. Balance oxygen using water –NO 3 - → NO + 2 H 2 O Balance hydrogen using H + –4 H + + NO 3 - → NO + 2 H 2 O

7. –Balance charge by adding electrons –Cu → Cu 2+ + 2e - – 3e - + 4 H + + NO 3 - → NO + 2 H 2 O

8. Equalize the electrons Lowest common multiple is 6 3[Cu → Cu 2+ + 2e - ] 2[3e - + 4 H + + NO 3 - → NO + 2 H 2 O]

9. Multiple each species by the multiple so that the electrons are equal in both half reactions. 3 Cu → 3 Cu 2+ + 6e - 6e - + 8 H + + 2 NO 3 - → 2 NO + 4 H 2 O ____________________________________ 3 Cu + 8 H + + 2 NO 3 - → 3 Cu 2+ + 2 NO + 4 H 2 O Anything that exists as a product and as a reactant can be crossed off

10. Balance the following: a)Cr 2 O 7 2- (aq) + S 2 O 3 2- (aq)  Cr 3+ (aq) + S 2 O 6 2- (aq) b) Mn 3+ (aq)  MnO 2 (s) + Mn 2+ aq) c) C 3 H 8(aq) + O 2(aq)  CO 2(aq) + H 2 O (l) State what is the reducing agent and the oxidation agent for the above reactions.