Redox Reactions in Basic Aqueous Solution?

Question

Balance the following equations, using the oxidation number method, and enter the coefficients in the boxes. The coefficients must be the smallest possible integers.

HPbO2- + Re + H2O + OH- Pb + ReO4- + OH- + H2O

Whats the oxidation number method?

Answer 1

The oxidation number method is used to balance a redox equation by solving the equation in 3 parts (some methods use 2, I like 3)- the oxidized species, the reduced species and to balance out O, H2O and OH-.

In your reaction, Pb+4 is reduced to Pb, while Re is oxidized from Re0 to Re+7. So we imagine that the electron released by the oxidization are used for reduction. Then we write:
Pb+4 + 4e -> Pb
Re -> Re+7 + 7e
To balance, we mult the Pb by 4 and the Re by 7
to get 7Pb+4 + 28e -> 7Pb
4 Re -> 4 Re+7 + 28e
Now we worry about the oxygen,water and hydroxide. With the Pb and Re, On the left, we have 7H and 14 O, and on the right , 16O. To balance this out, we need OH- on the left and H2O on the right. A little thought (and heavenly intervention) leads us to
7H+ + 14O -2 + 11(OH-) -> 16 O -2+ 9 H2O
So we have 7HPbO2+ 4Re+ 11 OH- ->
7Pb + 4 ReO4 - + 9 H2O