# What is the pH and pOH of 6.5 g of sodium hydroxide in 650 mL of water?

Feb 11, 2017

$p H + p O H = 14$ in aqueous solution.

#### Explanation:

And since, $p O H = - {\log}_{10} \left[H {O}^{-}\right]$, all we have to do is calculate the concentration of $H {O}^{-}$.

$\left[H {O}^{-}\right] = \frac{\frac{6.5 \cdot g}{40.00 \cdot g \cdot m o {l}^{-} 1}}{650 \times {10}^{-} 3 \cdot L} = 0.25 \cdot m o l \cdot {L}^{-} 1$

So $p O H = - {\log}_{10} \left(0.25\right) = - \left(- 0.60\right) = 0.60$

And $p H = 13.4$

Spare a thought for the students who did these calculations in the days before electronic calculators. Some 30-40 years ago, students of mathematics, and physics, and chemistry, would routinely use logarithmic tables for these calculations.