1. Balancing Oxidation Reduction Equations

2. Oxidation and Reduction
Oxidation – the atom loses electrons
The charge becomes more positive
Reduction – the atom gains electrons
The charge becomes more negative
Mass and charge must be conserved for all chemical equations.

3. Steps for Balancing Redox reactions
Acidic Solutions
Step 1: Write the half reactions for the oxidation and reduction.
MnO4- + H2SO3 SO42- + Mn2+ + H2O
(Mn goes from Mn7+ to Mn2+ so this is reduction)
MnO4-  Mn2+

4. Steps for Balancing Redox reactions
S goes from S4+ to S6+, so this is oxidation
H2SO3  SO42-
Step 2: Balance the half rxns for atoms other than H and O.
Already balanced for the example.
Step 3: Balance the O’s by adding H2O.
MnO4-  Mn2+ + 4H2O
H2O + H2SO3  SO42-

5. Steps for Balancing Redox Reactions
Step 4: Balance H atoms with H+
MnO4- + 8H+  Mn2+ + 4H2O
H2O + H2SO3  SO H+
Step 5: Balance the charge on each side by adding electrons.
MnO4- + 8H+  Mn2+ + 4H2O
total charge = +7  total charge = +2
So, add 5e- to the reactants side to balance the charge.

6. Steps for Balancing Redox Reactions
5 e- + MnO4- + 8H+  Mn2+ + 4H2O
H2O + H2SO3  SO H+
charge = 0 charge = 2+
So,
H2O + H2SO3  SO H+ + 2e-
Electrons must be added to opposite sides for each half reaction.

7. Steps for Balancing Redox Reactions
Step 6: Balance the electrons between both half reactions.
(5 e- + MnO4- + 8H+  Mn2+ + 4H2O) x 2
10 e- + 2MnO H+  2Mn2+ + 8H2O
(H2O + H2SO3  SO H+ + 2e-) x 5
5H2O + 5H2SO3  5SO H+ + 10e-
Now the electrons will cancel out

8. Steps for Balancing Redox Reactions
Step 7: Cross cancel the electrons and other substances.
10 e- + 2MnO H+  2Mn2+ + 8H2O
5H2O + 5H2SO3  5SO H+ + 10e-
Step 8: Add the half reactions together
5H2SO4 + 2MnO4-  2Mn2+ + 3H2O +
5SO H+ 3 4

9. Basic Solutions
Follow the same steps as for acidic solutions, and add the following steps.
Step 9: Add OH- to both sides to equal the H+
5H2SO3 + 2MnO4-  2Mn2+ + 3H2O +
5SO H+
4 OH-  4OH-

10. Basic Solutions Step 10: Combine the H+ and OH- to make water.
4 OH- + 5H2SO3 + 2MnO4-  2Mn2+ + 3H2O SO H2O
Step 11: Cancel the H2O if they are on both sides.
4 OH- + 5H2SO3 + 2MnO4-  2Mn2+ + 7H2O SO42-