# What is pH of a salt solution?

Aug 16, 2017

The $p H$ of the salt of a strong acid and a strong base is usually near as dammit to $p H = 7$ in aqueous solution.

#### Explanation:

And thus for strong acids mixed with 1 equiv of strong base we get....

$\text{KOH(aq)" +" HCl(aq)" rarr "KCl(aq)" + "H"_2"O(l)}$

$\text{NaOH(aq) + HClO"_4"(aq)" rarr "NaClO"_4(aq) + "H"_2"O(l)}$

Because neither chloride nor perchlorate is particularly basic (they are the conjugate bases of strong acids, and thus they do not compete strongly for the protium ion), the $p H$ of the solution is very close to $7$.

On the other hand, when 1 equiv acetic acid, a WEAK acid, is treated with 1 equiv of sodium hydroxide, the resultant solution is stoichiometric in ${\text{H"_3"CCO"_2^(-)"Na}}^{+}$. And this salt causes some hydrolysis, i.e.

$\text{H"_3"CCO"_2^(-)"Na"^(+)+"H"_2"O"(l) rightleftharpoons "H"_3"CCO"_2"H(aq)" +"NaOH(aq)}$

And thus at equivalence, the $p H$ of the solution will offset upwards from $p H = 7$ reflecting the equilibrium quantity of sodium hydroxide in solution.