BALANCING REDOX REACTIONS

Pg 646 - 651

Balancing Redox Reaction

Can use “old” way:

Ag (s) + Fe(NO3)3 (aq) Fe (s) + AgNO3 (aq)

But what if we have a reaction that looks like this….

MnO4- (aq) + Fe2+ (aq) Fe3+ (aq) + Mn2+ (aq)

acid

Half-Reaction Method

1. Separate the reaction into an oxidation half-reaction and a reduction half-reaction.

2. Balance ANY atom that isn’t an H or O in each reaction using coefficients.

Half-Reaction Method

3. Balance any O’s by adding water to the opposite side of the half-reaction.

4. Balance any H’s by adding H+ to the opposite side of the reaction.

Half-Reaction Method

5. Add electrons to each half-reaction so that the charges on both sides of the reaction are the same.

6. Balance the total number of electrons so they are EQUAL in both reactions.

Half-Reaction Method

7. Add the two half-reactions together

8. Check to make sure the atoms and charges balance!!

Let’s try one more!!

Balance the following redox reaction using the half-reaction method:

Pb (s) + PbO2 (s) + H+ (aq) Pb2+ (aq) + H2O (l)

Now you try one!!

Balance the following reaction using the half-reaction method:

Ni (s) + NO3- (aq) Ni2+ (aq) + NO2 (g)