# When dissolved in water, what do acids produce?

May 2, 2017

Dissolution of a gas in water causes an increase in the concentration of the characteristic cation of the solvent, i.e. ${H}_{3} {O}^{+}$, the $\text{hydronium ion}$.

#### Explanation:

We (well) know that water undergoes autoprotolysis......which we represent as:

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

And such protolysis may be quantitatively measured...

${K}_{w} = \left[{H}_{3} {O}^{+}\right] \left[H {O}^{-}\right] = {10}^{-} 14$

Taking ${\log}_{10}$ of both sides we get...........on rearrangement.

$- {\log}_{10} \left({10}^{-} 14\right) = - {\log}_{10} \left[{H}_{3} {O}^{+}\right] - {\log}_{10} \left[H {O}^{-}\right]$

But $- {\log}_{10} \left({10}^{-} 14\right) = - \left(- 14\right) = 14$ by definition, and also $p H = - {\log}_{10} \left[{H}_{3} {O}^{+}\right]$ and $p O H = - {\log}_{10} \left[H {O}^{-}\right]$, i.e. $p H + p O H = 14$.

And so the moral, dissolution of an acid in water causes AN INCREASE in the concentration of the characteristic cation, ${H}_{3} {O}^{+}$, and a DECREASE in $p H$.