Ammonium Chloride
Properties
| State | Solid at room temperature |
| Color | White crystalline powder |
| Solubility | Soluble in water (37.2 g/100 mL at 20 °C) |
| Melting Point | 338 °C (sublimes) |
| Boiling Point | 520 °C |
About Ammonium Chloride
Ammonium chloride is the canonical example of a salt of a weak base and a strong acid, which means a 1 M aqueous solution sits at pH 4.6 — close enough to acetate-buffer territory that students see the ammonium-cation hydrolysis pattern (NH4⁺ + H2O ⇌ NH3 + H3O⁺) in a way they can measure directly with a pH meter. The Ka of ammonium is 5.6 × 10⁻¹⁰, the conjugate of NH3's Kb of 1.8 × 10⁻⁵, and the resulting pH calculation is the textbook problem every general-chemistry student works through at least once. Beyond pedagogy, ammonium chloride has been used in metalwork for centuries as a flux for tinning, soldering, and galvanizing — heated against an oxide-coated metal surface, the salt sublimes, decomposes to NH3 and HCl, and the released HCl strips the oxide layer to expose clean metal that the solder or zinc can wet. The same sublimation behavior is the basis of theatrical 'smoke' effects: heat NH4Cl in one container, generate NH3 and HCl gases that diffuse and recombine in the cooler air to form a dense fog of finely divided ammonium chloride aerosol. The compound also gives Scandinavian and Dutch salmiak licorice its sharp, salty, slightly sour taste — the trigeminal-nerve response to ammonium chloride is what produces that distinctive 'almost too much' flavor that polarizes the candy aisle.
Where you'll encounter it
If you've worked with traditional zinc-carbon dry-cell batteries (the kind that came out of TV remotes before alkaline took over), the brown paste in the middle was a moist mixture of ammonium chloride, manganese dioxide, and carbon — NH4Cl was the electrolyte that ferried current between the zinc anode and the manganese-dioxide cathode. In a chemistry teaching lab, the heat-pack demonstration that uses ammonium chloride dissolution to absorb heat (ΔHsoln ≈ +14.8 kJ/mol) is the classic endothermic-process demo, useful for teaching that solubility doesn't require an exothermic process and that entropy can drive a reaction even when enthalpy resists it. The cold-pack version of this is sold commercially under several brand names and uses exactly the same chemistry.
Common Uses
- Flux for soldering, tinning, and galvanizing metal surfaces
- Electrolyte in zinc-carbon dry-cell batteries
- Ammonia-source nitrogen fertilizer in cooler-climate agriculture
- Salmiak licorice flavoring in Northern European confectionery
- Endothermic-dissolution demonstration for cold packs and teaching
Safety Information
Mildly irritating to skin and eyes in solid form; the dust and the sublimation fumes (which contain NH3 and HCl) irritate the airways. Large oral doses cause acidosis through the buffer mismatch of generating HCl in the stomach; the doses used in food are well within safe limits. GHS H302 and H319. Heat under ventilation and avoid generating dust clouds.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.