What is the OH^- concentraton of a solution that is 0.10M in Na2C2O4?

Question

I have a couple of these concentration questions asking different things but I don't know how to do them

Answer 1

For salts, like this one, you hydrolyze them; i.e., react them with water. Suppose we have 0.1 M NaA (the salt of NaOH and a weak acid). The general equation is
A^- + HOH ==> HA + OH^-

Kb = Kw/Ka = (HA)(A^-)/(HA)

You know Kw and Ka, (A^-) = 0.1 M and (HA)= (OH^-) = x
You solve for x, which in this case is (OH^-), take -log to obtain pOH, then subract from 14 to get pH.