* Ammonium ion (NH₄⁺) is a weak acid: When ammonium chloride dissolves in water, it dissociates into ammonium ions (NH₄⁺) and chloride ions (Cl⁻). The ammonium ion can donate a proton (H⁺) to water molecules, acting as a weak acid:

NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺

* Chloride ion (Cl⁻) is a neutral ion: Chloride ions are the conjugate base of a strong acid (HCl). They do not significantly affect the pH of the solution.

Therefore, the presence of the weakly acidic ammonium ion leads to an overall acidic solution.