Answer
The $[OH^-]$ of a solution decreases when the $[H_3O^+]$ is increased, and increases when the $[H_3O^+]$ is decreased.
Work Step by Step
According to the expression of the ion product constant for water:
$$K_w = [H_3O^+][OH^-]$$
- Dividing both sides by $[H_3O^+]$:
$$\frac{K_w}{[H_3O^+]} = [OH^-]$$
- $K_w$ is a constant, assuming constant temperature; therefore, $[OH^-]$ is inversely proportional to $[H_3O^+]$.
$$\frac{1}{[H_3O^+]} \propto [OH^-]$$
When $[H_3O^+]$ increases, $[OH^-]$ decreases and vice versa.
