Discussions on the equations of sodium acetate trihydrate-acetic acid buffer
The equations of sodium acetate trihydrate and acetic acid buffer formed by Fuzumin trihydrate need to be recognized first. Acetic acid ($CH_3COOH $), a weak acid, is partially ionized in water, and its ionization equation is $CH_3COOH\ rightleftharpoons CH_3COO ^ - + H ^ + $.

Sodium acetate trihydrate ($CH_3COONa · 3H_2O $), a strong electrolyte, is completely ionized in water, and its ionization equation is $CH_3COONa · 3H_2O\ longrightarrow CH_3COO ^ - + Na ^ ++ 3H_2O $.

When the two are co-placed in the solution, the ionization of sodium acetate trihydrate is $CH_3COO ^ - $, which will affect the ionization of acetic acid. According to the principle of Ellechatelier, due to the increase of the concentration of $CH_3COO ^ - $, the ionization equilibrium of acetic acid will shift to the left, inhibiting the ionization of acetic acid.

The principle of action of this buffer is that when a small amount of acid is added, the $CH_3COO ^ - $in the solution will bind to $H ^ + $, causing the ionization equilibrium of acetic acid to shift to the right, thereby consuming $H ^ + $, so that the pH value of the solution changes very little. The reaction can be abbreviated as $CH_3COO ^ - + H ^ +\ longrightarrow CH_3COOH $.

If a small amount of alkali is added, $OH ^ - $will react with the ionization of acetic acid, so that the ionization equilibrium of acetic acid shifts to the right, and the supplemental consumption of $H ^ + $, $pH $does not change significantly. The reaction is roughly $CH_3COOH + OH ^ -\ longrightarrow CH_3COO ^ - + H_2O $.

In summary, the main equilibrium relationship between sodium acetate trihydrate and acetic acid buffer revolves around the ionization equilibrium of acetic acid and the hydrolytic equilibrium of acetate ions. The two restrict each other, so that the solution pH $remains relatively stable, which is reflected in its core equation.