What is the concentration of OH - ions at a pH = 6?

Answer;

1 * 10^-8 M

Explanation;

pH is given by the - log[H+] while

pOH is given by the - log[OH-]

But;

pH + pOH = 14

Thus; if pH is 6, then pOH = 8

pOH = 8

-log[OH-] = 8

[OH-] = 10^-8 M

The concentration of OH - ions at a pH of 6 is 1 * 10^-8 M