Question

What is the percent dissociation of HX (pKa = 4.69) in a 0.383 M solution?

Answer 1

concentration = 0.383 M

pKa of HX = 4.69

Ka of HX = 2.04 x 10^-5

HX ----------------->   H+ +   X-

0.383                         0          0

0.383 - x                     x          x

Ka = [H+][X-] / [HX]

2.04 x 10^-5 = x^2 / (0.383 - x)

x = 0.00278

[H+] = x = 0.00278 M

% dissociation = ([H+] / initial concentraion ) x 100

                        = (0.00278 / 0.383) x 100

                        = 0.72 %

% dissociation = 0.72 %