Structural, Chemical and Physical Properties of Ammonia
Property Value or Detail
Molecular Mass 17.03 g/mol
Odour Sharp, Intensely Irritating
Physical State Gas (at room temperature)
Melting Point -77.7°C
Boiling Point -33.35°C
Flash Point 11°C
Decomposition Point 500°C
Density (Gas) 0.7710g/L
Density (Liquid) 0.6818g/L
Vapour Density 0.5697 (air has a vapour
density of 1)
Critical Temperature 132.4°C
Critical Pressure 111.3 atm
Heat of Fusion 58.1 kJ/mol
Heat of Vaporization 23.3 kJ/mol
Heat of Combustion -316 kJ/mol
Property Value or Detail
Chemical Formula NH3
Type of Base Weak
Affinity (Water) High
Corrosiveness Corrosive to Some Metals
Oxidation Power Strong Reducing Agent
Reactivity Quite Reactive
Volatility Increasing with increases in
Affinity for Water
Anhydrous Ammonia has a very high affinity for water, and
when it comes into contact with anything containing water it
becomes very caustic, and this can be very dangerous as it
can attack moist parts of the body if it comes into contact with
them. Despite the high affinity for water, ammonia has limited
reactivity with water.
The combustion of ammonia proceeds with difficulty but yields
nitrogen gas and water.
4NH + 3O + heat 2N + 6H O
However, with the use of a catalyst and under the correct
conditions of temperature--as described above in Oxyacids of
nitrogen and their salts--ammonia reacts with oxygen to produce
nitric oxide, NO, which is oxidized to nitrogen dioxide, NO , and
is used in the industrial synthesis of nitric acid.
Ammonia readily dissolves in water with the liberation of heat.
NH + H O NH +
These aqueous solutions of ammonia are basic and are
sometimes called solutions of ammonium hydroxide (NH OH).
The equilibrium, however, is such that a 1.0 molar solution of
NH provides only 4.2 millimoles of hydroxide ion. The hydrates
NH H O, 2NH H O, and NH 2H O exist and have been
shown to consist of ammonia and water molecules linked by
intermolecular hydrogen bonds.
Liquid ammonia is used extensively as a nonaqueous solvent.
The alkali metals as well as the heavier alkaline earth metals
and even some inner transition metals dissolve in liquid
ammonia, producing blue solutions. Physical measurements,
including electrical conductivity studies, provide evidence that
this blue colour and electrical current are due to the solvated
These solutions are excellent sources of electrons for reducing
other chemical species. As the concentration of dissolved
metal increases, the solution becomes a deeper blue in colour
and finally changes to a copper-coloured solution with a
metallic lustre. The electrical conductivity decreases, and there
is evidence that the solvated electrons associate to form
Most ammonium salts also readily dissolve in liquid ammonia.
Ammonia in Redox
Ammonia gas is a strong reducing agent
When dry ammonia gas is passed over heated black copper
oxide it will be reduced to brown copper.
3CUO + 2NH3 3Cu +N2 + 3H2O
It reduces lead monoxide to lead
3PbO 2NH3 3Pb + N2 + 3H2O
Ammonia reduces chlorine to hydrogen chloride
8NH3 + 3Cl2 6NH4Cl + N2
If chlorine is in excess
NH3 + 3Cl2 3HCl + NCl3 (nitrogen tri-chloride)
When a glass rod dipped in concentrated hydrochloric acid is
brought near ammonia it gives out dense white fumes of
ammonium chloride which is the confirmative test for ammonia
NH3 + HCl NH4Cl
Reaction with Nessler’s reagent K2 HgI4
When mercuric chloride is added to potassium iodide solution
scarlet red precipitate form which dissolves in excess of
mercuric chloride and become a clear solution without any
colour. This is known as Nesslers reagent.
When ammonia is passed over the Nesslers reagent it turns
pale brown. On passing excess of ammonia over it a brown
precipitate is obtained.
Ammonia consists of one Nitrogen atom bonded covalently to
three Hydrogen atoms, as can be seen in the above diagram.
The shape of the molecule can be said to be a triangular
pyramid and is dipolar.