Question

7A.   What is the % ionization of HPHO₃- (hydrogen phosphite ion) in an aqueous 1.000 M solution of the sodium hydrogen phosphite (half-neutralized phosphorous acid)?  

7B. What is the % ionization of HPHO₃- if the concentration is 0.00300 M?

7C. What is the % association 0.00300 M HPHO₃-?

Answer 1

7A. H2PO3- <==> H+ + HPO3^2-

Ka = [H+][HPO3^2-]/[H2PO3-]

1.66 x 10^-7 = x^2/1

x = [H+] = 4.07 x 10^-4 M

% ionization = [H+] x 100/[HA] = 4.07 x 10^-4 x 100 = 0.04

7B. Feeding values in Ka equation,

1.66 x 10^-7 = x^2/0.003

x = [H+] = 2.23 x 10^-5 M

% ionization = [H+] x 100/[HA] = 2.23 x 10^-5 x 100/0.003 = 0.74

7C. H2PO3- + H2O <===> H3PO3 + OH-

Kb = 1 x 10^-14/1.66 x 10^-7 = x^2/0.003

x = [OH-] = 1.34 x 10^-5 M

% association = 1.34 x 10^-5 x 100/0.003 = 0.45