How do I determine these concentrations?

Question

What are the concentrations of HSO4^- , SO4^2- , and H^+ in a 0.21 M HKHSO4 solution? (Hint: H2 SO4 is a strong acid; Ka for HSO4^- = 1.3 x 10^-2)

Answer 1

Do you mean 0.21 M KHSO4 solution by "0.21 M HKHSO4 solution"?
Let the concentration of SO4(2-) to be X: [SO4(2-)] = X, we have:
HSO4(-) ---> SO4(2-) + H+
(0.21-X).........X .............X
Since Ka for HSO4^- = 1.3 x 10^-2, we have:
X^2/(0.21 - X) = 1.3 x 10^-2 = 0.013
X^2 + 0.013X - 0.013*0.21 = 0
X = 0.046
[HSO4(-)] = 0.16M
[SO4(2-)] = 0.046M
and [H+] = 0.046M