If the acid dissociation constant, Ka, for an acid HA is 8 X 10-4 at 25°C, ?

Question

what

percent of the acid is dissociated in a 0.50 molar solution of HA at 25°C?

a. 0.08 %

b. 0.20%

c. 1 %

d. 2%

e. 4%

Answer 1

Ka = [H+] [A-] / [HA]

8e-4 =  [x] [x] / [0.5]

x = 0.02

% = 0.02 / 0.50 times 100 = 4%

your answer is e. 4%