Question

If the pH is 9 what is the concentration of hydroxide ion [OH]? (hint: find the pOH first)

Answer 1

Realize that pH + pOH = 14
so, 9 + pOH = 14 -> pOH = 5
pOH = -log[OH-]
5 = -log[OH-]
plug it into a calculator and you get 1.0 x 10^-5
alternatively, use [OH-] = 10^-pOH to get the same answer
[OH-] = 1.0 x 10^-5

Answer 2

The answer to this is 7