# If an acid is added to water, what would be the expected direction of the change in the pH of the water?

$p H$ will decrease, i.e. become more negative............
By definition, $p H = - {\log}_{10} \left[{H}_{3} {O}^{+}\right]$
Concentrated $\left[H C l \left(a q\right)\right]$ (34% w/w) is approx. $10 \cdot m o l \cdot {L}^{-} 1$, and thus its $p H = - {\log}_{10} \left(10\right) = - \left(1\right) = - 1$.
Most of the time when a $p H$ is quoted, the concentration will give rise to a positive $p H$.