# What does a solution with higher pH level indicate?

Feb 7, 2017

An alkaline solution.

#### Explanation:

We interrogate the auto-protolysis equilibrium:

$2 {H}_{2} O r i g h t \le f t h a r p \infty n s H {O}^{-} + {H}_{3} {O}^{+}$

See this old answer. In water, this equilibrium has been carefully measured, such that ${K}_{w} = \left[{H}_{3} {O}^{+}\right] \left[H {O}^{-}\right] = {10}^{- 14}$ at $298 K$.

We classify the acidity of the solution on the $p H$ scale, where $p H = - {\log}_{10} \left[{H}_{3} {O}^{+}\right]$. Given the negative function, numerically higher $p H$ values indicate that $\left[H {O}^{-}\right]$ is greater than ${10}^{-} 7$ $m o l \cdot {L}^{-} 1$, and, necessarily, $\left[{H}_{3} {O}^{+}\right]$ is LESS than ${10}^{-} 7$ $m o l \cdot {L}^{-} 1$.