Ammonium Chloride (NH₄Cl) – CAS 12125-02-9
Ammonium Chloride (NH₄Cl): Chemical Properties, Applications, and Prospects
1. Introduction
Ammonium chloride (also known as sal ammoniac) is an inorganic salt composed of ammonium (NH₄⁺) and chloride (Cl⁻) ions. It is a white crystalline solid with a sharp, saline taste. Highly soluble in water, it dissolves with an endothermic reaction, cooling the solution. Ammonium chloride is valued for its ability to provide a source of nitrogen and chloride ions, to act as a buffer, and to form complexes with metals. These properties make it a versatile compound used across a wide range of industries, including agriculture, metallurgy, pharmaceuticals, food processing, and textiles.
2. Chemical Structure and Nomenclature
Chemical name: Ammonium chloride
Molecular formula: NH₄Cl
Molecular weight: 53.49 g/mol
CAS number: 12125-02-9
EC number: 235-186-4
E number (food additive): E510
Synonyms: Sal ammoniac, ammonium muriate, chlorammonic, ammon salt, halophor
Appearance: White crystalline powder or colorless crystals; odorless; cooling, saline taste
3. Physicochemical Properties
Density: 1.527 g/cm³ at 20°C
Melting point: 337.8°C (sublimes without melting)
Boiling point: 520°C (at 760 mmHg); sublimes at 340°C
Solubility in water: 29.4 g/100 g at 20°C; 39.3 g/100 g at 50°C; 77.3 g/100 g at 100°C
pH (1% aqueous solution): 4.6–5.5 (weakly acidic due to hydrolysis of NH₄⁺)
Crystal structure: Cubic (cesium chloride-type)
Heat of solution: –16.1 kJ/mol (endothermic dissolution)
4. Synthesis Methods
Neutralization of ammonia with hydrochloric acid: The most common industrial method:
NH₃ + HCl → NH₄Cl
Ammonia gas or aqueous ammonia is passed through hydrochloric acid; the solution is evaporated and crystallized.
Solvay process by-product: Ammonium chloride is produced as a by-product in the Solvay process for sodium carbonate (Na₂CO₃), then separated and purified.
Double decomposition: Reaction of ammonium sulfate with sodium chloride:
(NH₄)₂SO₄ + 2 NaCl → 2 NH₄Cl + Na₂SO₄
5. Applications
Agriculture: Ammonium chloride is primarily used as a nitrogen fertilizer (containing 25–26% N in ammonium form). It is particularly effective for chlorine‑responsive crops such as rice, corn, wheat, coconut, oil palm, and vegetables. It provides a rapid nitrogen boost and is acid‑forming, making it suitable for neutral and calcareous soils. It also provides chloride (65–66% Cl), beneficial for certain crops.
Metallurgy and soldering: Used as a flux in galvanizing, tinning, and soldering to remove oxide coatings from metal surfaces and improve solder adhesion. Also used in electroplating, metal coloring, and cleaning soldering irons.
Batteries and electronics: Acts as an electrolyte in dry cell batteries (Leclanché cells) and in electronic applications.
Pharmaceuticals: Used as a systemic acidifying agent for treating metabolic alkalosis, as an electrolyte replenisher, and as a diuretic. Also used as an expectorant in cough syrups to help clear lung secretions. Available in oral and injectable formulations.
Food industry: Registered as food additive E510 – used as an acidity regulator, flour treatment agent, and flavor enhancer. Particularly popular in Scandinavian countries for salty liquorice (salmiakki) and to give cookies a crisp texture.
Textiles and leather: Used in textile dyeing as a mordant, in lustering cotton, and in leather tanning.
Analytical chemistry and laboratories: Used as a buffer solution component, analytical reagent, and in the manufacture of dyes and explosives.
6. Safety and Toxicology
Acute toxicity: Harmful if swallowed (H302). Oral LD₅₀ in mice is ~1300 mg/kg.
Eye and skin irritation: Causes serious eye irritation (H319); potential skin irritant and skin sensitizer.
Inhalation: Inhalation of dust may cause respiratory irritation, coughing, and dyspnea.
Systemic toxicity: May cause systemic toxicity by acidosis; caution required in patients with liver, kidney, or cardiac disease.
Environmental toxicity: Toxic to aquatic life with long-lasting effects (H411).
Storage: Store in a cool, dry, well‑ventilated area. Protect from moisture; avoid contact with strong bases (releases ammonia gas) and strong oxidizers.
7. Regulatory Status
Ammonium chloride is approved for use as a food additive (E510) in many countries. It is listed as an acceptable non‑medicinal ingredient in Canada and is permitted in cosmetics in the US, EU, and China. For pharmaceutical use, it is available as an injection (USP) and in oral formulations. In agriculture, it is widely used as a nitrogen fertilizer.
8. Conclusion
Ammonium chloride (NH₄Cl, CAS 12125-02-9) is a versatile inorganic compound with a wide range of applications across agriculture, metallurgy, electronics, pharmaceuticals, food processing, and textiles. Its high water solubility, acidic nature in solution, and ability to provide both nitrogen and chloride ions make it an indispensable industrial chemical. While generally safe at recommended concentrations, proper handling precautions should be observed due to its irritant and toxic properties at high doses. Ongoing research continues to explore new applications in green chemistry, nanotechnology, and advanced materials.