How do you calculate the pH of a solution when given the OH- concentration?

1 Answer

The pH + pOH = 14

The pOH = -log[OH-]

The pH is measure of acidity of a solution whereas the pOH is a measure of basicity of a solution.

The two expressions are opposites expressions. As the pH increases the pOH decreases and vice versa. Both values equal 14.

To convert a concentration of into pH or pOH take the -log of molar concentration of the hydrogen ions or the molar concentration of the hydroxide ion concentration respectively.

pH = -log [ H+]

pOH = -log [OH-]

For example if the [OH-] = 0.01 M, the -log [0.01 ] = 2.0

This is the pOH.
To determine the pH perform the following calculation.

pH = 14.0 - 2.0
pH = 12.0