Question

Calculate the concentrations of all species in a 0.950 M Na2SO3 (sodium sulfite) solution. The ionization constants for sulfurous acid are Ka1 = 1.4× 10–2 and Ka2 = 6.3× 10–8.

Answer 1

SO32-   + H2O   ------------------> HSO3- + OH-

0.950                                                0            0

0.950 - x                                           x             x

Kb2 = x^2 / 0.950 - x

1.59 x 10^-7 = x^2 / 0.95 - x

x = 3.88 x 10^-4

[HSO3-] = [OH-] = 3.88 x 10^-4 M

[H+] = 2.58 x 10^-11 M

[SO32-] = 0.9496 M

[H2SO3] = Kb1 = 7.14 x 10^-13 M