Chapter 7B- AMMONIA

Srinidhi Singh
Date: 8 April 2020
DISCOVERY
 In 1774 – Joseph Priestley prepared
NH3 gas from Slaked lime and Sal
ammoniac (NH4Cl).
 In 1785 – Berthelot studied the
chemical composition of the gas.
 In 1800 – Davy established its basic
composition and proved it to be a
compound.
OCCURRENCE
 Free state – atmospheric air and natural
water
( Decay of nitrogenous matter in absence of
air)
water-cycle.svg

 Combined state – Ammonium salts and

ammoniacal liquor
LABORATORY METHOD -1
NOTE :
 Reaction involved:
 2NH4Cl+Ca(OH)2CaCl2+2H2O+2NH3
 Passed through quicklime to produce
dry ammonia ( Drying agent )
 Collected by - downward displacement
of air (lighter than air; vapor density is
8.5)
 Cannot be collected over water due to
high solubility(1vol - 702vol)
REACTANTS
 1.Higher ratio of weight of alkali –To counteract
the loss by sublimation of ammonium chloride
on heating
 2.Ca(OH)2 – Cheap and not deliquescent
 3.Ammonium nitrate not used – Explosive in
nature and decomposes to form nitrous oxide
and water vapor (unlike ammonia)
 4.Flask (Inclined position) – Water vapor formed
does not trickle back and crack the hot flask
 5.Reactants(Ground) – Maximum surface area
for reaction
Drying the gas
 Agent used – Quicklime (CaO)
 Not used – conc.H2SO4,P2O5,fused CaCl2
 1.They react chemically
 2. a. 2NH3 + H2SO4  2(NH4)2SO4
 b.6NH3 + P2O5 + 3H2O  2(NH4)3PO4
 C.8NH3 + CaCl2  CaCl2.8NH3
(addition product)
LABORATORY METHOD – 2
Nitrides – Expensive-Seldom
used
 Mg3N2+6H2O3Mg(OH)2+2NH3
 Ca3N2 +6H2O 3Ca(OH)2 +2NH3
 AlN+3H2OAl(OH)3+NH3↑AlN+3H2O
 Ammonia liberated is collected by
holding the collecting jar mouth
downwards over delivery tube. Gas is
dried by passing it through CaO packed
in a drying tower
 Warm water is used in the process
HABERS PROCESS – Industrial
method
EQUATION
Catalyst – Iron(III)oxide
Promoter – 1% K2O and 3% Al2O3
Impurities – CO,CO2 and H2S (N2 and H2
must be free from them)
 The manufacture of ammonia by Haber's process
involves the direct combination of N2 and H2.
 Nitrogen is obtained by fractional distillation of liquid air
 Hydrogen is obtained from water gas (Bosch process)
 N2 is also prepared by heating ammonium nitrite (or a
mixture of sodium nitrite and ammonium chloride)
 NH4NO2 →N2↑+2H2O
 Reactants should be free from impurities – tend to poison
the catalyst and reduce its effectiveness.
 This reaction is (a) Reversible, (b)
Exothermic, and (c) Proceeds with a
decrease in volume.
 According to the Le Chatelier's principle,
the favorable conditions for the
formation of ammonia are
 Low temperature
 High pressure
 Catalyst (Molybdenum or alumina)
Temperature
 Optimum Temperature – 450 – 500oC
 If reaction is exothermic – Higher yield is

favored by lowering the temperature

according to Le Chatelier’s principle
 But if temperature is low – Speed of

reaction will be low and yield of

ammonia is also low
 Hence an optimum temperature is used
 Above this temperature – Ammonia –

Decomposes – N2 and H2
PRESSURE
 An optimum pressure of 200-900 atm is
used
 If reaction proceeds with decrease in volume
( 4vol  2vol) forward reaction is favored by
increasing the pressure.
If pressure is too high – Production plant
may not withstand the pressure and might
blast.
Hence an optimum pressure is used
( 250atm )
CATALYST
 Finely divided iron
 Promoter – Molybdenum
 Catalyst does not affect the yield of
ammonia
Collection of the gas – NH3
LIQUIFACTION DISSOLVING IN
Ammonia is easily WATER
liquefiable Ammonia is highly

-33oC at 8atm soluble in water.

pressure 1 vol – 702 vol

N and H are N and H are

2 2 2 2
difficult to liquify almost insoluble in
 (-196/-253oC) water
PHYSICAL PROPERTIES OF
AMMONIA
 Colorless , Pungent , Alkaline in taste
 Affects respiratory system if inhaled and is
fatal in high doses.
 Lighter than air
 Highly soluble in water
 Easily liquifies at low temperature
FOUNTAIN EXPERIMENT
 High solubility in
water
 Basic in nature
CHEMICAL PROPERTIES OF
AMMONIA
1.COMBUSTIBILITY
 Reaction with oxygen
 Ammonia if ignited
does not burn.
 Burns in O2 with
greenish yellow or
green flame
 4NH3+3O22N2+6H2O
 Irreversible, highly
exothermic.
CATALYTIC OXIDATION
Catalytic oxidation of
ammonia
Ammonia reacts with O2 at
800∘C in the presence of
Platinum to give nitric oxide
and H2O. (This reaction is
used in the Ostwald process
for manufacture of nitric acid)
4NH +5O 6H O+4NO↑
3 2 2

2NO+O2NO2(brown gas)


Platinum continues to glow

even after heating is
discontinued since its an
exothermic reaction
2. Basic Nature of Ammonia.

 Ammonia gas is basic in nature

 Dry ammonia gas is neutral to litmus.
( ammonia is a weak base.
 But it changes the moist red litmus blue
showing that its solution is basic in
nature. It also changes phenolphthalein
pink.
Reactions are :
 Ammonia in its aqueous solution neutralizes
acids forming respective salts.
 NH3 + H2O  NH4OH
 NH4OH ----- NH4+ + OH1-

 1.NH3 + HCl  NH4Cl

 2.NH4OH + HCl  NH4Cl + H2O
 3.2NH4OH+H2SO4(NH4)2SO4+2H2O
 4.NH4OH+HNO3NH4NO3+H2O
Ammonium chloride is an ammonium SALT
which undergoes thermal dissociation on
heating.
 Aqueous solution of ammonia
precipitates hydroxides of metals from
their solution of the salts giving the
following color of its hydroxides as
precipitate
 Ferrous hydroxide (dirty green)
 Ferric hydroxide (reddish brown)
 Lead hydroxide (white)
 Copper hydroxide (pale blue)
 Zinc hydroxide (white gelatinous)
IRON
FeCl3 + 3NH4OH  3NH4Cl + Fe(OH)3

(reddish brown)
LEAD
Pb(NO3)2 + 2NH4OH  2NH4NO3 + Pb(OH)2
( chalky white)
ZINC
ZnSO4 + 2NH4OH  (NH4)2SO4 + Zn(OH)2
(WHITE
GELATINOUS)
IRON
FeSO4+2NH4OH (NH4)2SO4+Fe(OH)2↓
(Dirty green ppt. insoluble in
excess of NH4OH)
COPPER
CuSO +2NH OH (NH ) SO +Cu(OH) ↓
4 4 4 2 4 2

(Pale blue
ppt. , dissolves in excess of NH4OH, to form
deep blue soluble complex salt – tetra
amine copper [II] sulphate)

Cu(OH)2+
(NH4)2SO4+2NH4OH[Cu(NH3)SO4]+4H2O
 The precipitates which are hydroxides of
metallic radicals vary in
 Color
 Solubility in excess NH4OH –
 And hence NH4OH
 IS USED IN QUALITATIVE ANALYSIS FOR
IDENTIFYING POSITIVE RADICALS OR
CATIONS.
3. Ammonia Gas – Reducing
action
 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 ( Buff
Yellow to Grayish metallic lead)
 3PbO + 2NH3 3Pb + N2 + 3H2 O
AMMONIA REDUCES
CHLORINE
1. Ammonia reduces chlorine to hydrogen
chloride
 If ammonia in excess


8NH3 + 3Cl2  6 NH4Cl + N2
Dense white fumes
 If chlorine is excess


NH3 + 3Cl2  3HCl + NCl3
(nitrogen trichloride)
Yellow oily pungent smelling explosive liquid
Tests for ammonia

 1.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
2. Reaction with Nessler’s reagent K2 HgI4
 When ammonia is passed over the
Nesslers reagent it turns pale brown.
 On passing excess of ammonia over it a
brown precipitate is obtained.
3. By passage of ammonia gas
through
 Copper sulphate solution:
CuSO4 + 2NH4OH  (NH4)2 SO4 + Cu(OH)2
 The pale blue ppt. turns into a deep blue
coloration solution on passage of excess
ammonia.
Uses of ammonia
 industrial uses
 as a source of

hydrogen, nitric
acid
 Liquor ammonia-

as a cleansing
agent
 Liquid ammonia –

refrigerant in ice
plants
Liquid ammonia acts as
a refrigerant in ice plants.
Evaporation of a liquid needs heat
energy.
 1When liquid ammonia vaporizes, it

absorbs large quantities of heat without

changing its temperature. For these
reasons, ammonia is widely used as
a refrigerant ( IT HAS A HIGH LATENT
HEAT OF EVAPORATION)
 IT IS HIGHLY VOLATILE

 EASILY LIQUIFIES UNDER PRESSURE AT

LOW TEMPERATURES.
As a cleansing agent
 Liquor ammonia emulsifies or dissolves
fats, grease, etc.
 An aqueous solution of ammonia in
water
 It is used to clean window panes,
porcelain articles, etc.
 P l ea
R ev s e
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