PLEASE ANYONE HELP ME, im so stuck on this question

Question

Compare the pH of a 0.55 mol/L H2SO4(aq) solution with the pH of a 0.55 mol/L of H2SO3(aq). Which solution contains the higher concentration of H3O+(aq) ions?

a) Detemine the Kb for the conjugate base of H2SO3(aq).

b) Determine the pH of a 0.20 mol/L solution of HSO3-(aq).

Answer 1

In order to solve this problem, one needs to know the Ka for H2SO4 (Ka1 and Ka2) and the Ka for H2SO3 (Ka1 and Ka2).

Looking up these values I have ...

H2SO4 ==> H⁺ + HSO4^- Ka1 = large

HSO4^- ==>H⁺ SO4^2-  Ka2 = 1.2x10^-2

 

H2SO3 ==> H⁺ + HSO3^-  Ka1 = 1.2x10^-2

HSO3^- ==> H⁺ + SO3^2-  Ka2 = 6.6x10^-8

 

0.55 M H2SO4 contains a higher concentration of H3O⁺ than 0.55 M H2SO3

a) K_b of conjugate base of H2SO3 is the K_b for HSO3^- which is 1x10^-14/Ka1 = 1x10^-14/1.2x10^-2 =  8.33x10^-11

b) HSO3^- ==> H⁺ + SO3^2-

Ka₂ = 6.6x10_^-8 = [H⁺][SO3^2-]/[HSO3^-] = (x)(x)/0.20

x² = 1.32x10^-8

x = 1.15x10^-4 M = [H⁺]

pH = -log [H⁺] = -log 1.15x10^-4

pH = 3.94