Find the pH of an aqueous solution

Question

What is the pH of 0.19 M aqueous KClO solution? The pKa of hypochlorous acid is 7.53.

Answer 1

Let’s look at what happens when you put KClO in water

KClO ==> K⁺ + ClO^-

The ClO^- then gets hydrolyzed as follows:

ClO^- +H₂O ==> HClO + OH^-

We are looking at the reaction of ClO^- acting as a base so we need the Kb. This is obtained as follows:

pKa + pKb = 14

pKb = 14 - 7.53 = 6.47

Kb = 3.39x10^-7

Kb = [HClO-][OH-] / [HClO]

3.39x10^-7 = (x)(x) / 0.19-x. Ignoring x in denominator ...

x² = 6.44x10^-8

x = 2.54x10^-4 = [OH-]

[H+] = 1x10^-14 / 2.54x10^-4

[H+] = 3.94x10^-11

pH = -log 3.94x10^-11

pH = 10.4