NH4Cl
Ammonium chloride

Chemical properties

Ammonium chloride forms colorless, octahedral crystals that smell of ammonia. When heated in a test tube, the ammonium chloride appears to sublimate. In reality, however, it decomposes at 338 °C. In the presence of air humidity above 350 °C, the substance decomposes completely into ammonia and hydrogen chloride.

The ammonia molecules escape faster than the hydrogen chloride molecules due to their lower mass. Therefore the indicator paper turns blue-green (ammonia) in the upper area and red (hydrogen chloride) in the lower area. At the cooler points in the test tube the two gases react again to form ammonium chloride. This reversible reaction is typical of an equilibrium reaction:

NH3 + HCl → NH4Cl

Ammonium chloride dissolves in water under strong cooling. It is also soluble in ethyl alcohol, but not in ether and acetone. The aqueous solution (on the photo below left) reacts acidic, a 10% ammonium chloride solution has a pH value of about 5.0 at 25 °C (in the middle a neutral solution of sodium chloride and on the right in comparison an alkaline solution of sodium acetate).

Production

In the laboratory and in the chemical industry ammonium chloride can be produced by introducing ammonia into hydrochloric acid. However, it is also produced in large quantities in the Solvay process during the production of sodium carbonate (see there).

Even the ancient Egyptians made sal ammoniac by heating manure from camels. The amines contained in it produced a white smoke of ammonium chloride with common salt. The word ammonia is derived from the term “Sal ammoniacum”. This refers to a salt that was allegedly found in the Ra Ammon oasis. The Arab chemist Dschabir ibn Hayyan described the production of ammonium chloride by distilling hair in 760 AD.

Use

Ammonium chloride is needed as electrolyte in dry batteries. The soldering salt required for soldering contains ammonium chloride, which evaporates due to the heat. The hydrogen chloride formed in this process, together with the simultaneously released ammonia, dissolves the oxide layers on the metal surface. This creates a good conductive contact. The same process is also used for galvanizing and tinning metals.

Ammonium chloride as the most important ammonium salt is used in many technical applications, for example

  • in the tannery
  • in textile printing
  • in the case of analogue photography in the fixing bath or
  • in the production of weather explosives.

A refrigeration mixture for cooling can be prepared by dissolving ammonium chloride in water or by adding ice cubes. The ammonia pastilles available in pharmacies contain liquorice and anise oil in addition to ammonium chloride, and have an expectorant effect.

Security

In one reported individual case, daily doses of eight grams of ammonium chloride led to acidosis after several weeks, which determines the symptoms even at higher doses. In the case of existing liver or kidney disease or potassium deficiency, appropriate caution is required.