(NH4)2CO3
Ammonium carbonate

Chemical properties

The salt forms a colourless powder with a faint smell of ammonia. It has a density around 1,6 g-cm-3 (at 20 °C). In aqueous solution it reacts weakly basic, a balance is established between ammonia NH3, ammonium ions NH4+, carbonate ions CO32-, hydrogen carbonate ions HCO3- and carbon dioxide CO2. The pH value of a 10% aqueous solution at 25 °C is 9.4.

The salt thus reacts with water to form hydrogen carbonate and hydroxide ions. An aqueous solution of ammonium carbonate is therefore only stable in a neutral and weakly basic environment - carbon dioxide gas escapes in acidic solutions, and ammonia gas in concentrated alkaline solutions.

Ammonium carbonate decomposes in air, and the reaction is violent when heated.

Production

Ammonium carbonate can be prepared by reacting carbon dioxide with ammonia in aqueous solution.

2 NH3 + H2O + CO2 → (NH4)2CO3

A further representation possibility results from heating calcium carbonate together with ammonium sulphate.

CaCO3 + (NH4)2SO4 → CaSO4 + (NH4)2CO3

With the latter method, in addition to the desired ammonium carbonate, ammonium hydrogen carbonate and ammonium carbamate also sublime off, leaving calcium sulphate as a solid.

Use

Ammonium carbonate is used in the synthesis of heterocycles and as an additive for photographic developers. It is also used in the dyeing industry as a mordant, as a spotting agent and as a carbon dioxide developer in fire extinguishers.

It is also used as a baking agent (as a component of deer horn salt). In the EU it is approved as food additive number E 503i.

It was also used earlier as a smelling salt to revive in cases of dizziness and fainting spells.

Ammonium carbonate is often used in inorganic chemistry for a qualitative analysis in order to precipitate the alkaline earth metal cations of barium, strontium and calcium as one group from an unknown sample in the cation separation reaction, to separate them and to identify them by means of detection reactions.

It is also used in the production of catalysts, foams, hair treatment products and casein paints and glues.