How will you explain buffer action of aqueous solution of ammonium acetate?

Ammonium acetate on dissolution dissociates completely as ions.

(i) If an acid (say HCl) is added to this solution, H₃O⁺ ions generated by the acid combine with CH₃COO^– ion to form weakly ionised acetic acid molecules

Since most of H₃O⁺ ions are consumed by CH₃COO^– ions to form slightly dissociated acetic acid, hence the pH value of the solution does not undergo any change.
Now suppose a base (say NaOH) is added to ammonium acetate solution. The OH^– ions liberated by the base will be consumed by ions to form very slightly dissociated NH₄OH. 


Since most of the OH^– ions are consumed by the  ions, hence there is very little or no change in the pH value of ammonium acetate.
Thus, CH₃COONH₄ has reserve acidity due to  ions and reserve alkalinity due to CH₃COO^– ions.