Ammonia

What is ammonia?

Ammonia is a gas of molecular formula NH3 with a molecular weight (17 g/mol). It has a density under normal conditions of 0.7714 g/L. It has a melting point (pf = -77.8 ºC) and a boiling point (bp = -33.4 ºC). It is very soluble in water (at 0 ºC one volume of NH3 mixes with 1176 volumes of H2O).

ammonia
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3D structure

It is a colorless gas that has a pungent odor, and in the presence of pure oxygen reacts (burns) to give nitrogen gas and water in the subsequent combustion reaction:

4NH3 + 3O2 2N2 + 6H2O

Gaseous ammonia is irritating to eyes and respiratory tract. When mixed with air in a proportion between 16-27 %, it results in an explosive combination at a temperature of 780 ºC. It is the main precursor of synthetic nitrogen compounds. For example, nitric acid is obtained by the Ostwald method when ammonia burns with oxygen in the presence of a platinum catalyst:

NH3 + 2O2 –(cat. platino) 2H2O + HNO3

At elevated temperatures, it readily decomposes to give nitrogen and hydrogen gas:

2NH3 2N2 + 3H2

Ammonia is obtained by Haber process and is mainly used in the preparation of ammonium sulfate and also in the preparation of Solvay process (soda process).