Ammonium chloride

N 1
H 4
Cl 1

6 atoms in one formula unit of an ionic lattice.

The drawing shows one formula unit of an ionic lattice, not a molecule; ammonium chloride has no molecular shape.

IUPAC name: azanium chloride
Molar mass: 53.489(12) g/mol
Atoms: 6
SMILES: [NH4+].[Cl-]
InChIKey: NLXLAEXVIDQMFP-UHFFFAOYSA-N
PubChem CID: 25517

Made of

Strong heat takes ammonium chloride from solid to vapour with no liquid stage between, a change called sublimation. The vapour is not the salt itself but a mixture of ammonia and hydrogen chloride. Its IUPAC name is azanium chloride, and its two ions hold nitrogen, hydrogen and chlorine between them. At room temperature it is an odourless solid, colourless to white and hygroscopic, which means it takes up water from the air.

Water dissolves 39.5 g of it per 100 g at 25 °C, on the figure of HSDB, the Hazardous Substances Data Bank. Alcohol dissolves it too, while acetone, ether and ethyl acetate barely do. Dissolving it is strongly endothermic: the salt takes in heat as it goes into solution. The balance of energies behind such a heat change is traced on the calcium chloride page.

Structure and bonding

An ammonium ion and a chloride ion make the drawing’s two pieces, with no line between them. The ammonium ion, NH₄⁺, is a nitrogen atom joined to four hydrogen atoms by single bonds, the only lines in this drawing of one formula unit. The chloride ion, Cl⁻, stands apart. The drawing puts the +1 on the nitrogen as a formal charge, an electron count kept for bookkeeping, and gives the hydrogens none. How ammonia gains its fourth hydrogen is told on its own page.

In the solid no NH₄Cl pair stands alone. Its crystals are colourless and cubic in HSDB’s description, and the salt takes two crystal forms, depending on temperature. Why such a lattice holds together is set out in chemical bonding.

In water the ions separate. A small share of the ammonium ions then give up one of their four hydrogens, as a proton, to a water molecule, leaving ammonia and forming hydronium, H₃O⁺. The proton comes from the cation itself, Chem1 notes, and since the transfer goes only a little way, the solution is only slightly acidic.

Where it turns up

The old name, sal ammoniac, means “salt of Amun”. In Chem1’s account it was a crystalline crust, formed where the smoke of camel-dung fires, North Africa’s everyday fuel, met cool surfaces. Heating the crust released a sharp-smelling gas, which T. Bergman named ammonia, a name drawn from the salt. Sal ammoniac is still a synonym for the salt, according to MeSH, the National Library of Medicine’s Medical Subject Headings. NIOSH, the US National Institute for Occupational Safety and Health, calls the fume sal ammoniac fume.

It goes into washing powders and into a snow treatment that slows melting, HSDB records. Rice and wheat growers use it as a nitrogen source, though none is made for fertiliser in the United States and some arrives from Europe now and then. Bakery products carry it as an additive. Cosmetics use it for buffering, holding acidity steady, and to control thickness, and craftworkers use it to apply patinas to metal.

Why it matters

Industry recovers ammonium chloride as a by-product of the Solvay process for sodium carbonate. It is also made from ammonia and hydrochloric acid, or from sodium chloride with an ammonium salt, according to HSDB. In 1984, by HSDB’s figures, 35 per cent of its use went into the electrolyte of dry cells, whose paste the zinc page describes. Flux, the agent laid on metal before soldering or coating, took 30 per cent, and galvanising, which coats metal with zinc, 15 per cent. The salt also serves in refining zinc by electrolysis and in etching printed circuit boards.

Ammonium is made in the body too, where it helps keep acid and base in balance, and medicine uses the salt as a systemic and urinary acidifier. The liver turns its ammonium into urea and frees a hydrogen ion, which reacts with bicarbonate to give water and carbon dioxide. In HSDB’s account, the net result is chloride taking bicarbonate’s place. It also acts as a diuretic, causing a net loss of fluid from outside the cells.

Properties

Properties of ammonium chloride Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 25517.
Property	Value	Unit	Source
Formula (Hill order)	ClH₄N
Molar mass	53.489(12) g/mol	g/mol	IUPAC/CIAAW 2024
Nitrogen atoms	1
Hydrogen atoms	4
Chlorine atoms	1
PubChem molecular weight	53.49 g/mol	g/mol	PubChem

Safety

Under its EU classification ammonium chloride is harmful if swallowed and causes serious eye irritation, with the signal word Warning. HSDB rates it an irritant of the eyes, skin and airways. Galvanising releases its fume in large amounts, and NIOSH lists cough and breathlessness among that fume’s effects. The PubChem Laboratory Chemical Safety Summary for ammonium chloride and NIOSH’s card on the fume carry the full classification and the workplace exposure limit.

Questions

What is the pH of an ammonium chloride solution?

Mildly acidic. HSDB, the Hazardous Substances Data Bank, gives a pH of 5.5 for a 1 per cent solution at 25 °C, falling to 5.1 at 3 per cent and 5.0 at 10 per cent. The International Chemical Safety Cards call the solution a weak acid. The dry solid drifts the same way with age: over long storage it gives up ammonia and grows more acidic, HSDB notes.

What happens when ammonium chloride is heated?

It sublimes rather than melting, at 338 °C on HSDB's figure, or at 662 °F, which is 350 °C, on NIOSH's. Where the vapour meets a cool surface, the salt can settle out again. Strongly heated, it breaks down and gives off toxic, irritating fumes of nitrogen oxides, ammonia and hydrogen chloride, though it does not itself burn.

Why is ammonium chloride used in baking?

It strengthens dough and helps it rise. Those are two of the jobs for which US federal rules at 21 CFR 184.1138 affirm it as generally recognised as safe in food, alongside flavour enhancer and processing aid. HSDB names bakery products among the foods that carry it. JECFA, the international expert committee on food additives, classes it as a flour treatment agent and a yeast food.

Is ammonium chloride used in cough medicine?

It has been. The salt irritates the mucous membranes, and that irritation gives it an expectorant effect, an expectorant being a medicine meant to help bring up mucus; the US National Cancer Institute's thesaurus records its use for coughs. The US Food and Drug Administration lists it among expectorant ingredients with inadequate data for over-the-counter use, and HSDB notes that no oral form is sold commercially in the US any more.