# How do you determine the pH of a solution that has a hydroxide concentration of 9.3*10^-16 M? Is this solution acidic or basic?

Apr 14, 2016

You can determine it like this:

#### Explanation:

Assuming we have aqueous conditions, water dissociates:

${H}_{2} {O}_{\left(l\right)} r i g h t \le f t h a r p \infty n s {H}_{\left(a q\right)}^{+} + O {H}_{\left(a q\right)}^{-}$

${K}_{w} = \left[{H}_{\left(a q\right)}^{+}\right] \left[O {H}_{\left(a q\right)}^{-}\right] = {10}^{- 14} {\text{mol"^2."l}}^{- 2}$ at ${25}^{\circ} \text{C}$

This means that $\left[O {H}_{\left(a q\right)}^{-}\right] = {10}^{- 7} \text{mol/l}$ from the ionisation of water.

An $O {H}_{\left(a q\right)}^{-}$ concentration of $9.3 \times {10}^{- 16} \text{mol/l}$ is vanishingly small in comparison so I would say that the solution is neither acid or alkali but neutral.