# Why is the pH scale 0-14?

Mar 17, 2014

Actually, the pH scale is not limited to 0-14, but most common solutions fall into this range.

The pH of a solution is calculated as the negative base-10 logarithm of the hydronium ion (${H}_{3} {O}^{+}$) concentration in solution.

Example 1: A 0.01 M solution of HCl (a strong acid that completely dissociates to ${H}_{3} {O}^{+}$ and $C {l}^{-}$) is given by
pH = -log(0.01) = 2.0

Example 2: A 1.0 M solution of HCl has a pH of
pH = -log(1.0) = 0.0

Example 3: A 2.0 M solution of HCl has a pH of
pH = -log(2.0) = -0.30