Ammonium Chloride: Acidic Properties, Composition, and Practical Uses

By Sushil Khadka – Updated August 30, 2022

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Ammonium chloride (NH₄Cl), commonly called sal ammoniac, is a white crystalline salt formed by the reaction of ammonia (NH₃) with hydrochloric acid (HCl). It is highly soluble in water and, when dissolved, produces a solution that is slightly acidic.

TL;DR

Ammonium chloride is a water‑soluble salt of ammonia that yields a slightly acidic solution. In water, chloride ions generate H⁺, while ammonium ions produce OH⁻ through equilibrium with ammonia.

Aqueous Ammonium Chloride

Dissolving NH₄Cl crystals in water initiates a series of equilibria:

NH4Cl(s) ⇌ NH4⁺(aq) + Cl⁻(aq)
NH4⁺(aq) + H2O(l) ⇌ NH3(aq) + H3O⁺(aq)
H3O⁺(aq) + OH⁻(aq) ⇌ 2 H2O(l)

These reactions show that the salt splits into its constituent ions, and the ammonium ion can act as a weak base while the chloride ion can contribute to acidity via the formation of HCl in solution.

Acidic Component

In aqueous solution, chloride ions associate with water to form hydrochloric acid:

Cl⁻(aq) + H2O(l) ⇌ HCl(aq) ⇌ H⁺(aq) + Cl⁻(aq)

Because HCl is a strong acid, the overall solution has a slight acidic character.

Basic Component

Ammonium ions equilibrate with water to generate ammonia and hydroxide:

NH4⁺(aq) + H2O(l) ⇌ NH3(aq) + OH⁻(aq)

This weak base counterbalances the acidity but does not fully neutralize it, leaving the solution slightly acidic.

Acidic Nature and Uses

The modest acidity of ammonium chloride can be confirmed with a pH meter, typically falling between 5.5 and 6.5. Its practical applications include:

• Fertilizer: Provides readily available ammonia for crops such as corn, wheat, barley, and rice.
• Snow Treatment: Applied to ski slopes above 0 °C (32 °F) to harden snow and improve traction.

Its role in agriculture and winter sports demonstrates its versatility and importance in everyday chemistry.