What is the concentration of SO3^2- in a 0.043 M solution of Sulfurous acid (H2SO3) in water? The value of Ka1 for H2SO3 is 1.300 x 10-2 and the value of Ka2 is 6.300 x 10-8.

Answer 1

H2SO3 ==> H^+ + HSO3^-
HSO3^- ==> H^+ + SO3^2-

k1 is much larger than k2; therefore, H^+ is essentially equal to HSO3^-. So we write
k2 = (H^+)(SO3^2-)/(HSO3^-)
Since (H^+) = (HSO3^-), then
(SO3^2-) = k2.