# Why do we use the pH scale to indicate the acidity of a solution rather than simply stating the concentration of hydronium ions?

Which is easier to say: that $p H = 10$, or that $\left[{H}_{3} {O}^{+}\right] = {10}^{-} 10 \cdot m o l \cdot {L}^{-} 1$? Besides, you have to be able to ask your A level students something.