Answer
Hydronium ion: $[H_3O^+] = 7.1 \times 10^{- 9}M$
Hydroxide ion: $[OH^-] = 1.4 \times 10^{- 6}M$
Work Step by Step
1. Calculate the hydronium ion concentration.
$[H_3O^+] = 10^{-pH}$
$[H_3O^+] = 10^{- 8.15}$
$[H_3O^+] = 7.079 \times 10^{- 9}M$
2. Use this value to calculate the hydroxide ion concentration:
$[H_3O^+] * [OH^-] = Kw = 10^{-14}$
$ 7.079 \times 10^{- 9} * [OH^-] = 10^{-14}$
$[OH^-] = \frac{10^{-14}}{ 7.079 \times 10^{- 9}}$
$[OH^-] = 1.413 \times 10^{- 6}M$
