If a substance increases the OH - concentration of pure water by 10^4. what is the pH of the solution?

pH = 11

Explanation:

The concentration of OH⁻ in pure water is 10⁻⁷ M. If a substance increases OH⁻ concentration by 10⁴, the new concentration will be:

[OH⁻] = 10⁴ x 10⁻⁷ M = 10⁻³M

We can calculate pOH using it's definition:

pOH = - log[OH⁻] = - log (10⁻³) = 3

Then, we can find out pH using the following relation:

pH + pOH = 14

pH = 14 - pOH = 14 - 3 = 11

Since pH = 11 is higher than 7, we can confirm that the substance is a base.