What is the pH of a 0.0055 M HA (weak acid) solution that is 8.2% ionized
A) 2.26
B) 3.35
C) 4.52
D) 8.21
E) 10.65

Question

Quizplus · Accepted Answer

First, we need to calculate the Ka (acid dissociation constant) of the weak acid using the ionization percentage:

% ionization = (concentration of ionized HA / initial concentration of HA) x 100
8.2 = (concentration of H+ and A- / 0.0055) x 100
0.00451 = concentration of H+ and A-

Ka = [H+][A-] / [HA]
Ka = [0.00451][0.00451] / (0.0055 - 0.00451)
Ka = 3.49 x 10^-5

Then, we can use the Henderson-Hasselbalch equation to calculate the pH:

pH = pKa + log([A-] / [HA])
pH = -log(3.49 x 10^-5) + log(0.00451 / (0.0055 - 0.00451))
pH = 3.35

What Is the PH of a 0