1. Balancing Oxidation-Reduction Reactions in Acidic & Basic Solutions
Chapter 4.10
Balancing Oxidation-Reduction Reactions
in Acidic & Basic Solutions

2. Balancing Oxidation-Reduction Equations
Half-Reaction Method:
Separate the full equation into 2 half-reactions (oxidation and reduction)
Balance each half-reaction separately
Add them together to get full balanced equation

3. Balancing in ACIDIC solution
1. Write separate equations for the oxidation and reduction half-reactions
2. For each half-reaction:
Balance all elements BUT H and O
Balance O using H2O
Balance H using H+
Balance charge using electrons (e-)
3. If necessary, multiply one or both half-reactions to ensure equal numbers of electrons transferred in the two half-reactions
4. Add half-reactions together & cancel identical species
5. Check to make sure elements and charges are balanced

4. MnO4- (aq) + Fe+2(aq) Fe+3(aq) + Mn+2(aq)
Balance the following redox reaction in acidic solution:
MnO4- (aq) + Fe+2(aq) Fe+3(aq) + Mn+2(aq)
1. Write the separate half-reactions
2. Balance each half-reaction

5. 3. Equalize the electron transfer in the two half-reactions
4. Add the two half-reactions and cancel identical species

6. Balance the following redox reaction in acidic solution:
H+(aq) + Cr2O7-2(aq) + C2H5OH(l) Cr+3(aq) + CO2(g) +H2O(l)
1. Write the separate half-reactions
2. Balance each half-reaction

7. 3. Equalize the electron transfer in the two half-reactions
4. Add the two half-reactions and cancel identical species

8. Balancing redox reactions in BASIC solution
1. Balance using acidic method
2. Add OH- ions to both sides, equal to #H+ ions
3. Form water on the side of equation that contains both ions
4. Simplify # water molecules
5. Check balancing

9. Balance in BASIC solution:
Ag(s) + CN-(aq) + O2(g) Ag(CN)2-(aq)
1. Write the separate half-reactions
2. Balance each half-reaction

10. 3. Equalize the electron transfer in the two half-reactions
4. Add the two half-reactions and cancel identical species

11. 5. Add OH- ions to both sides of the equation to equal the # of H+
6. Form water on the side contain both ions (H+ and OH-) & simplify H2O molecules

12. PRACTICE...PRACTICE...PRACTICE !