# How do you determine pH from molarity?

Mar 6, 2014

Molarity is also known as the concentration. The concentration can be converted to $\text{pH}$.

Take a sample of nitric acid ${\text{HNO}}_{3}$ with a molarity of $\text{0.0032 M}$.

The molarity becomes the $\left[{\text{H}}^{+}\right]$ concentration of $3.2 \times {10}^{- 3}$.

We know this is the $\left[{\text{H}}^{+}\right]$ concentration because ${\text{HNO}}_{3}$ is a strong acid, since the acid will completely dissociate into ${\text{H}}^{+}$ and ${\text{NO}}_{3}^{-}$.

To find the $\text{pH}$ calculate $- \log \left[{\text{H}}^{+}\right]$

$- \log \left[3.2 \times {10}^{- 3}\right] = 2.49 = \text{pH}$

To find the $\text{pOH}$ take the $\text{pH}$ value and subtract it from $14$.

$14 - 2.49 = 11.51 = \text{pOH}$

To convert $\text{pOH}$ to $\left[{\text{OH}}^{-}\right]$ calculate $\left[\text{OH"^-]=10^(-"pOH}\right)$

${10}^{- 11.51} = 3.09 \times {10}^{- 12} = \left[{\text{OH}}^{-}\right]$