Question

A weak acid, HF, is prepared with an initial concentration of 1.20 M. After reaching equilibrium, it has a pH of 1.551. What is the percent ionization of this acid? Select one: 4.2% 0.84% 2.4% None of these 0.082%

Answer 1

.               HF      $\rightleftharpoons$      H⁺      + OH^-

Initial 1.2 M.             0              0

Change.    -x    +x         +x

Change.     (1.2-x)M    xM     x M

Given pH = 1.551

Since pH = - log [H⁺]

H⁺ = 0.0281 M

Percentage ionisation of the acid = (acid amount ionized/ initial acid )X100= (0.0281 M/1.2 M)X100= 2.34 Answer