Question

Calculate the concentrations of H2SO3, H3O+, HSO3-, and SO32- in a 0.025 M H2SO3(aq) solution

Answer 1

Look up k1 and k2 for H2SO3. k2 is so much smaller than k1 that the majority of the H^+ will be furnished by k1 and "almost" none by k2.
.........H2SO3 ==> H^+ + HSO3^-
initial.0.025M......0......0
change...-x..........x......x
equil....?..........x........x

k1 = (H^+)(HSO3^-)/(H2SO3)
Substitute and solve for x = (H^+)=(HSO3^-)

...........HSO3^- ==> H^+ + SO3^2-
Note from above that (H^+) = (HSO3^-)
k2 = (H^+)(SO3^2-)/(HSO3^-)
Since (H^+) = (HSO3^-) (almost anyway), then (SO3^2-) = k2.