CHEMISTRY STUDY OF COMPOUNDS - AMMONIA
Ammonia
Ammonia
Molecular formula: NH3
Relative molecular mass: 17 amu
Lewis diagram or dot diagram
Preparation of Ammonia Gas
General methods of preparation
2NH4Cl + Ca(OH)2 CaCl2 + 2H2O + 2NH3
(NH4)2SO4 + 2NaOH Na2 SO4 + 2H2O + 2NH3
(NH4)2SO4 + 2KOH K2SO4 + 2H2O + 2NH3
Laboratory Preparation
From Ammonium Chloride
Reactants: Ammonium chloride (NH4Cl) and calcium hydroxide [Ca (OH)2] in the ratio
of 2:3 by weight.
Reaction:
2NH4Cl + Ca (OH)2 → CaCl2 + 2H2O +2NH3
Collection:
Ammonia gas is collected by the downward displacement of air because it is
i. Lighter than air (VD of NH3 = 8.5 and that of air = 14.4).
ii. Highly soluble in water, and therefore, it cannot be collected over water.
From Metal Nitrides
It can also be prepared by the action of warm water on nitrides of metals such as magnesium or
aluminium.
Reaction:
AlN + 3H2O
Al (OH)3+ NH3
Or
Mg3 N2 + 6H2O
3Mg (OH)2 + 2NH3
RAHUL MEHRA/M-9873005334
1
CHEMISTRY STUDY OF COMPOUNDS - AMMONIA
Manufacture of Ammonia (Haber process)
Reactants: Nitrogen and hydrogen in the ratio of 1:3 by volume.
Reaction: N2 + 3H2 2NH3 +Heat
Physical Properties of Ammonia
Colourless, alkaline in nature, strong, pungent choking smell, slightly bitter in taste.
Vapour density of ammonia is 8.5.
Easily liquefied at 10°C by compressing it at 6 atm. pressure.
Boiling point is −33.5°C, and freezing point is −77.7°C.
It is highly soluble in water.
Chemical Properties of Ammonia
i. Ammonia reacts with acids to form corresponding ammonium salts.
NH3 + HCl NH4Cl
Ammonium chloride
2NH3 + H2 SO4 (NH4)2SO4
Ammonium sulphate
ii. Ammonia dissolves in water to form an aqueous solution of NH4OH.
NH3 + H2O NH4OH
Ammonium hydroxide
iii. Ammonia reduces heated metallic oxides to produce metals, water vapour and nitrogen.
2NH3 + 3CuO 3Cu + 3H2 O + N2
iv. W hen conc. solution of NH3 is added to conc. solution of copper sulphate, a light blue ppt. of copper
(II) hydroxide is formed.
NH3 + H2O NH4OH
CuSO4 + 2NH4 OH
Cu(OH)2 + (NH4)2 SO4
Copper (II) hydroxide
RAHUL MEHRA/M-9873005334
2
CHEMISTRY STUDY OF COMPOUNDS - AMMONIA
2+
Cu (OH)2 + (NH4)2 SO4 + 2NH4OH
[Cu(NH3)4] SO4-2 + 4H2O
Tetrammine copper (II) sulphate (Deep blue)
v. Decomposes into elements at high temperature or by electric sparks.
2NH3 N2 + 3H2
vi. Burns in oxygen with a yellowish-green flame to produce nitrogen and water vapour.
4NH3 + 3O2
2N2 + 6H2O
vii. Ammonia reacts with oxygen to produce nitric oxide and water vapour in the presence of platinum at
800°C.
viii. W hen ammonia reacts with excess of chlorine, it forms nitrogen trichloride and HCl.
NH3 + 3Cl2
NCl3 + 3HCl
Nitrogen trichloride
ix. W ith limited amount of chlorine, it forms ammonium chloride and nitrogen.
8NH3 + 3Cl2
6NH4Cl + N2
x. Ammonium hydroxide reacts with soluble salts of metals to produce insoluble precipitates of their
respective metallic hydroxides.
FeSO4 + 2NH4 OH → (NH4)2SO4 + Fe (OH)
Uses of Ammonia
Liquid ammonia is used as a refrigerant in ice plants.
As a laboratory reagent in qualitative analysis because it produces characteristic coloured metallic
hydroxide precipitates.
In the manufacture of fertilisers (e.g. ammonium sulphate and diammonium hydrogen phosphate) and
explosives (e.g. ammonium nitrate).
In the manufacture of sodium carbonate by the Solvay process and nitric acid by the Ostwald process.
RAHUL MEHRA/M-9873005334
3
CHEMISTRY STUDY OF COMPOUNDS - AMMONIA
Manufacture of Nitric Acid
Step 1: Catalytic oxidation of Ammonia
A mixture of dry air and dry ammonia in the ratio of 10:1 by volume is compressed and then passed into
platinum gauze which acts as catalyst at about 800°C.
4NH3 + 5O2 4NO +6H2O +Heat
Step 2: Oxidation of Nitric Oxide
Nitric oxide combines with oxygen to form nitrogen dioxide at about 50°C.
2NO +O2 2NO2
Step 3: Absorption of Nitrogen Dioxide in Water
The nitrogen dioxide and oxygen present in the air react with water to form nitric acid.
4NO2 +2H2O +O2 → 4HNO3
Nitric acid obtained is concentrated above 50%. On further distillation, 68% nitric acid is produced.
RAHUL MEHRA/M-9873005334
