AMMONIA
AMMONIA
Ammonia is
anhydride of nitrogen formed when an ammonia salt is heated with a non-volatile
base. In nature, ammonia is produced when nitrogenous matter decays in the
absence of air by the action of heat or putrifying bacteria.
LABORATORY
PREPARATION OF AMMONIA
Ammonia is prepared
in the laboratory by heating a mixture of powdered calcium hydroxide and
ammonium chloride.
Ca(OH)2 +
2NH4Cl
CaCl2 + 2H2O + 2NH3
Calcium hydroxide
is preferred because it is cheap and not deliquescent. The ammonia gas evolved
on heating is dried by passing it through calcium oxide and then collected by
upward delivery.
For the fact that
the gas is alkaline, the usual drying agent like conc. H2SO4 and CaCl2 are not
used for drying it, as they react with the gas.
INDUSTRIAL
PREPARATION OF AMMONIA [HABER PROCESS]
Ammonia is obtained
industrially by the haber process: which is based on the direct combination of
nitrogen and hydrogen.
N2 + 3H2 2NH3
Since the reaction
is reversible, special conditions of reaction are required for the optimum
yield of NH3. The process involves mixing N2 and H2 in the volume ratio of 1:3
at a relative high pressure of about 200 atmosphere and passed over a catalyst
of finely divided iron mixed with alumina at a temperature of 450oC.
The ammonia
produced is liquefied by cooling and stored for further use.
PHYSICAL PROPERTIES
OF AMMONIA
1.
Ammonia is a colourless gas with a characteristic
pungent smell.
2.
It is less dense that air.
3.
It is an alkaline gas, therefore it turns moist
red litmus paper blue.
4.
Ammonia is very soluble in water.
5.
In large quantities ammonia is poisonous.
6.
It has a boiling point of -77.8oC and melting
point of -33.4oC
7.
It is easily liquefied into a colourless liquid
at ordinary temperature.
CHEMICAL PROPERTIES
OF AMMONIA
1.
Reaction with oxygen: Ammonia burns readily in
oxygen to form water vapour and nitrogen.
4NH3g +
3O2g 6H2Og
+ 2N2g
In the presence of
heated platinum catalyst, ammonia reacts with excess oxygen to produce nitrogen
(II) oxide and water.
4NH3g +
O2g platinum 4NOg + 6H2Ol
2.
Ammonia as a reducing agent: Ammonia is not a
strong reducing agent. It reduce chlorine to hydrogen chloride and nitrogen.
2NH3g +
3Cl2g 6HClg + N2g
The hydrogen
chloride then react with excess ammonia to produce dense white fumes of ammonia
chloride.
6NH3g + 6HClaq 6NH4Cls
If chlorine is in
excess, nitrogen trichloride, an explosive and oily liquid is formed.
3.
Reaction with carbon(IV)oxide: Ammonia reacts
with carbon(IV)oxide at 150oC and a high pressure of 150 atmosphere to produce
urea, an important organic compound.
2NH3 + CO2 (NH2)2CO + H2O
4.
As a base: Ammonia is a weak base, it reacts with
acids to form ammonia salts.
2NH3g +
H2SO4aq
(NH4)2SO4s
If hydrogen
chloride gas is used, dense white fumes composed of suspended particles of
ammonium chloride are formed.
NH3g +
HClg
NH4Cls
5.
Thermal decomposition: Ammonia decomposes at
temperature above 500oC to yield nitrogen and hydrogen.
2NH3g N2g + 3H2g
TEST FOR AMMONIA
1.
Action of litmus paper: Hold a damp red litmus
paper into the jar containing the unknown gas. If the litmus paper turns blue
then the gas is ammonia.
2.
Action with hydrochloric acid: Dip a glass rod in
concentrated hydrochloric acid and then insert it in the gas jar containing the
unknown gas. White fumes are formed if the gas is ammonia.
USES OF AMMONIA
1.
It is used in the manufacture of fertilizer,
trioxonitrate(v) acid and sodiumtrioxocarbonate(IV) by solvay process.
2.
Aqueous ammonia is used in softening hard water.
3.
Liquid ammonia is used in refrigerators as a
cooling agents.
4.
In the production of nylon.
5.
Aqueous ammonia is also used in laundries as
solvent for removing grease and oil stain.
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