What is the pH of a 4*10^-2 M HCl solution?

Apr 27, 2016

$p H$ $=$ $- {\log}_{10} \left[{H}_{3} {O}^{+}\right]$ $=$ $- {\log}_{10} \left(4.0 \times {10}^{-} 2\right)$ $=$ $1.40$
$p H$ $=$ $- {\log}_{10} \left[{H}_{3} {O}^{+}\right]$ $=$ $- {\log}_{10} \left(4.0 \times {10}^{-} 2\right)$
We assume (reasonably) that hydrochloric acid will undergo complete dissociation in water to give stoichiometric ${H}_{3} {O}^{+}$ ion, according to the given reaction:
$H C l \left(a q\right) + {H}_{2} O \left(l\right) \rightarrow {H}_{3} {O}^{+} + C {l}^{-}$