On the pH of Ammonium Acetate Aqueous Solution

If you want to know the pH of ammonium acetate in water, you must understand the reason for its hydrolysis. Ammonium acetate is a salt of weak acid acetic acid and weak base ammonia water.

Acetate ion ($CH_3COO ^ - $) will bind to water ionized hydrogen ion ($H ^ + $), hydrolysis reaction occurs: $CH_3COO ^ - + H_2O\ rightleftharpoons CH_3COOH + OH ^ - $, which increases the concentration of hydroxide ion ($OH ^ - $) in the solution.

Ammonium ion ($NH_4 ^ + $) also binds to the hydroxide ion ionized by water, and the hydrolysis reaction is: $NH_4 ^ ++ H_2O\ rightleftharpoons NH_3 · H_2O + H ^ + $, which increases the concentration of hydrogen ion ($H ^ + $) in the solution.

The ionization constant of acetic acid $K_a $is similar to the ionization constant of ammonia water, about the same order of magnitude. When ammonium acetate is dissolved in water, the degree of hydrolysis of acetate ion and ammonium ion is equivalent. Therefore, the concentration of hydrogen ion in the solution is nearly equal to the concentration of hydroxide ion, and the solution is neutral, that is, its pH is about 7. From this perspective, the pH of ammonium acetate aqueous solution is the result of the mutual check and balance of its anion and cation hydrolysis. Because the corresponding acid-base ionization constants are similar, the degree of hydrolysis is similar, and the solution is finally neutral.