Exercise 6 | The Properties of Acids and Bases
A 0.10 M solution of a weak acid HX is 0.86 % ionized.
What is the pKa of this solution?
The equation for the reaction is:
HX (aq) + H2O (l) X- (aq) + H3O+ (aq)
% dissociation = x 100
⇒ [H3O+] = % dissociation x = 8.6 x 10-4 M
From the stoichiometry of the reaction: [X-] = [H3O+]
And [HX] = [HX]0 - [H3O+]
Ka = = 7.5 x 10-6
pKa = - log Ka = 5.1