How does salt change the pH of water?

1 Answer
anor277
Jun 16, 2016

Common salt, NaCl, the stuff with which you season your fish and chips, does not change the pH of water.

Explanation:

NaCl is the salt of a strong acid and a strong base. The salt does not affect equilibrium values of [H_3O^+] and [HO^-]:

HCl(aq) + NaOH(aq) rarr NaCl(s) + H_2O

The reaction as written lies strongly to the right.

On the other hand we could perform the equivalent reaction with the weak acid, hydrogen fluoride:

HF(aq) + NaOH(aq) rightleftharpoons H_2O(l) + NaF(aq)

The sodium fluoride product would participate in the back reaction to some extent, and a solution of NaF in water would give a slightly basic solution:

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