Answer to Question #9036 in Inorganic Chemistry for Jordan M Maxwell

Question

Calculate the fluoride ion concentration and pH of a solution that is 0.20 M in
HF and 0.10 M in HCl

Answer 1

HCl is strong acid and strong electolytet,his means that it breaks up into ions completely,so pH is -log[H⁺] = -log[HCl] = -log[0.1] = 1, but HF is weak acid and
it breaks up into ions not compleatly,and we need to use K_a which is 3.39 x
10^-4, so pH for HF is:

K_a = [H⁺][F^-]/[HF] = [H⁺]^2/[HF]
[H⁺]^2 = K_a[HF] = 3.39 x 10^-4 * 0.1 = 3.39 x 10^-5
[F^-] = [H⁺] = (3.39x 10^-5)^1/2 = 0.0058
pH = -log[H⁺] = 2.237