The method of calculating the pH value of ammonium acetate

If you want to calculate the pH value of ammonium acetate (Ammonium Acetate), you need to know the reason. Ammonium acetate is a salt composed of weak acid (acetic acid) and weak base (ammonia water).

In water, both acetate ion ($CH_3COO ^ - $) and ammonium ion ($NH_4 ^ + $) can be hydrolyzed. The hydrolysis of acetate ion makes the solution alkaline, and the hydrolysis equation is: $CH_3COO ^ - + H_2O\ rightleftharpoons CH_3COOH + OH ^ - $; the hydrolysis of ammonium ion makes the solution acidic, and the hydrolysis equation is: $NH_4 ^ ++ H_2O\ rightleftharpoons NH_3 H_2O + H ^ + $.

Let the concentration of ammonium acetate be $c $ (mol/L), the ionization constant of acetic acid is $K_a $, and the ionization constant of ammonia water is $K_b $.

For acetate ion hydrolysis, $K_ {h1} =\ frac {K_w} {K_a} $ ($K_w $is the ionic product constant of water); for ammonium ion hydrolysis, $K_ {h2} =\ frac {K_w} {K_b} $.

From proton conservation, $[H ^+] + [ CH_3COOH] = [NH_3 H_2O] + [OH ^ -] $.

Because $K_ {h1} $and $K_ {h2} $are all small, and the hydrolysis of acetate ions and ammonium ions in ammonium acetate inhibits each other, it can be approximated as $[CH_3COOH]\ approx [NH_3 · H_2O] $.

Then $[H ^ +]\ approx [OH ^ -] $, the solution is close to neutral. When accurately calculated, the expression of the relevant equilibrium constant can be combined with the equations of material conservation and charge conservation, and the exact pH value can be obtained after complex algebraic operations.

is probably the method of calculating the pH value of ammonium acetate, that's all. Scholars should understand the principles and be familiar with the methods in order to obtain accurate numbers, which are beneficial to the research and use of chemistry.