Question

The pH of Chloroacetic acid solution is 1.71 Based on the pH and the pKa of 2.85 what percentage of the Chloroacetic acid is in HA(protonated) form

Answer 1

pH = 1.71

[H+] = 10^-1.71 = 0.0195 M = x

Ka = 10^-pKa = 1.41 x 10^-3

HA <----------------------> H+   + A-

C -x                                  x         x

Ka = x^2 / C -x

1.41 x 10^-3 = x^2 / C- x

1.41 x10^-3 = 0.0195^2 / C -x

C -x = 0.269

C = 0.269 + x = 0.269 + 0.0195

C = 0.2885 M

percent unprotonated form = ( x / C ) x100

                                       = (0.0195 / 0.2885) x 100

                                       = 6.76 %

percent protonated form = 100 -.6.76

                                     = 93.24 %