# The pOH of a solution is 10.75. What is the concentration of OH^- ions in the solution?

Feb 21, 2017

#### Answer:

$\left[H {O}^{-}\right] = {10}^{- 10.75} = 1.78 \times {10}^{-} 11 \cdot m o l \cdot {L}^{-} 1$

#### Explanation:

$p O H$ is defined the same way as $p H$, except that here we address hydroxide ion concentration, i.e. $p O H = - {\log}_{10} \left[H {O}^{-}\right]$......and thus $\left[H {O}^{-}\right] = {10}^{- p O H} = {10}^{- 10.75}$.

Remember that since $p {K}_{w} = p H + p O H$

$- {\log}_{10} {10}^{-} 14 = - {\log}_{10} \left[{H}_{3} {O}^{+}\right] - {\log}_{10} \left[H {O}^{-}\right]$

$- \left(- 14\right) = p H + p O H = 14$