Question

What is pH of a salt solution?

Answer 1

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

Explanation:

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

`"KOH(aq)" +" HCl(aq)" rarr "KCl(aq)" + "H"_2"O(l)"`

`"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 `pH` 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 `"H"_3"CCO"_2^(-)"Na"^(+)`. And this salt causes some hydrolysis, i.e.

`"H"_3"CCO"_2^(-)"Na"^(+)+"H"_2"O"(l) rightleftharpoons "H"_3"CCO"_2"H(aq)" +"NaOH(aq)"`

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