NITROGEN AND ITS COMPOUNDS
is a covalent compound. It has a molecular mass of 17.
PREPARATION OF AMMONIA
– Round bottomed flask, clump, Bunsen burner, delivery tube,
trough, curd board, wire gauze, lime water.
Chemicals – Calcium hydroxide, Ammonium chloride,
Ammonia is prepared by heating a mixture of calcium hydroxide and
+ 2NH4Cl(s) CaCl2(s)
+ 2H2O(i) + 2NH3(g)
The tube in which ammonia is generated is fixed in a slanting position
to prevent the water formed from running back and crack the whole
sulphuric acid and anhydrous calcium chloride are not used to
dry ammonia because they react with it. Ammonia is collected
by upward delivery as it is lighter than air.
HABER PROCESS (INDUSTRIAL PREPARATION)
– Compressing chamber, catalytic chamber, cooling chamber,
Chemicals – Finely divided iron, Alminium Oxide, Water, Hydrogen,
is manufactured by reacting Nitrogen and hydrogen in the presence
of finely divided iron as a catalyst at temperatures 350ºC
- 400ºC at a pressure of about 350 atmospheres.
+ 3H2(g) 2NH3(g)
Oxide is added to the catalyst to improve its performance. It makes
it more porous and this provides a high surface area to the reaction.
The reaction is reversible hence it is not possible to convert all
the reactants into ammonia.
To separate ammonia from the mixture is cooled, only ammonia liquidfies
and it is separated.
The uncombined Nitrogen and hydrogen are recycled.
Another way of separation is to pass the mixture into water.
Only ammonia dissolves.
AFFECTING THE REACTION (PROCESS)
pressure causes a better yield of ammonia because it favours the
formation of the smaller products. It also increases the speed of
reaction because the reacting molecules collide more often.
low temperatures the yield at equilibrium of Ammonia is higher but
the reaction is slow. At high temperatures the yield of ammonia
is low but the reaction is fast, a temperature of about 500ºC
is used. The yield is good but the reaction is still too slow. A
catalyst is therefore necessary to speed up the reaction.
catalyst speeds the reaction but does not affect the equilibrium.
The catalyst should be finely divided because reaction occurs only
at the surface.
is a colorless gas with a characteristic pungent smell.
turns dump / wet red litmus paper blue. It is the only common
forms dense white fumes with hydrogen chloride gas
+ HCl(g) NH4Cl(s)
Ammonia diffuses faster and white dense fumes will be formed near
hydrogen chloride gas – the white dense fume is ammonia chloride.
is very soluble in water. The great solubility of ammonia can
be demonstrated using the fountain experiment.
largely dry, round bottomed flask with ammonia is used. The mouth
of the flask is placed under water and a red litmus paper in a trough
of gas jar. It is clamped firmly in position. The spring clip at
the end of the long glass tube is opened. Water slowly rises up
the tube until one drop is at the jet at the top.
The drop dissolves so much ammonia that there is a partial vaccum
in the flask.
Water is sucked rapidly up the tube and enters the flask as a fountain.
The litmus paper turns blue.
burns in a lot of air (oxygen). The flame is yellow green.
+ 3O2(g) 6H2O(i)
Glass wool is to spread out the oxygen in order to bring it into
greater contact with ammonia.
presence of a catalyst ammonia reacts with oxygen to form nitrogen
monoxide. The monoxide is easily oxidized to dioxide hence if a
hot platinum or copper wire is suspended in a beaker of concentrated
ammonia and oxygen is bubbled through the solution, redish brown
fumes are seen. The fumes later turn white. The brown fumes are
due to nitrogen dioxide which turn white as ammonium nitrate is
+ 5O2(g) 4NO(g)
+ O2(g) 2NO2(g)
+ O2(g) + 2H2O(i) 4HNO3(g)
reduces heated copper(II) oxide to copper i.e. copper turns
from black to brown.
CuO(s) + 2NH3(g) 3
Cu(s) + 3H2O(i) + N2(g)
burns in chlorine forming mist of hydrogen chloride gas. In
excess ammonia, dens white fumes of ammonia chloride are formed.
+ 3Cl2(g) N2(g)
+ 3 NH3(g) NH4
solution (Ammonium hydroxide) contains hydroxyl ions with metal
ions precipitates of the hydroxides are formed. Hence a blue
precipitate forms when aqueous ammonia is added to copper II
sulphate solution. The precipitate dissolves in excess ammonia
forming a deep blue solution.
Iron(II) is (Fe2+) forms a dirty green precipitate with
ammonia insoluble in excess Iron(III) is (Fe3+) forms
a brown precipitate insoluble in excess.
is used in the manufacture of fertilizers e.g. Ammonium sulphate.
is used in softening water.
is used in making nitric acid.
is used in making plastics.
chloride is used in dry cells.
is used in making explosives.
is the only common alkaline gas known. It changes the dump /
wet litmus paper blue.
forms dense fumes of ammonium chloride when brought into contact
with fumes of hydrogen chloride from concentrated hydrochloric