Calculate pH, pOH, hydrogen ion concentration ([H+]) and hydroxide ion concentration ([OH–]) for a range of solutions

Acid/Base Reactions > Using Brønsted–Lowry Theory >

Problem Statement:

Calculate the pH, pOH and [H⁺] of 0.01M CH₃COOH solution when the percentage of dissociation is 12.5%.

Solution:

Since CH₃COOH is a weak acid, it dissociates partially in aqueous solution as follows

Given,
Percentage of dissociation = 12.5%
so, [H⁺] = 0.01 × 12.5%
= 0.01 × 0.125M
= 1.25 × 10^-3 M

Now, pH = – log[H⁺] = – log (1.25 × 10^-3)
= 2.903
and pOH = 14 – pH
= 14 – 2.903
= 11.097

Problem Statement:

Calculate the pH, pOH and [OH^–] of 0.05M NH₄OH solution when the percentage of dissociation is 7.5%.

Solution:

Since NH₄OH is a weak base, it dissociates partially in aqueous solution as follows

Given,
Percentage of dissociation = 7.5%
so, [OH^–] = 0.05 × 7.5%
= 0.05 × 0.075M
= 3.75 × 10^-3 M

Now, pOH = – log[OH^–] = – log (3.75 × 10^-3)
= 2.426
and pH = 14 – pOH = 14 – 2.426
= 11.574