Study of Compounds

B: Ammonia

Grade - 10 [ICSE]
 Syllabus
● Laboratory preparation from ammonium chloride
and collection; (the preparation to be studied in
terms of, setting of the apparatus and diagram,
procedure, observation, collection and identification)
● Ammonia from ammonium salts using alkalies.
The reactions to be studied in terms of reactants,
products, conditions and equations.
● Manufacture by Haber’s Process.
● Density and solubility of ammonia (fountain
experiment).
● The burning of ammonia in oxygen.
 Syllabus
● The catalytic oxidation of ammonia (with conditions and
reaction)
● Its reactions with hydrogen chloride and with hot
copper (II) oxide and chlorine (both chlorine in excess
and ammonia in excess).
All these reactions may be studied in terms of reactants,
products, conditions, equations, and observations.
● Aqueous solution of ammonia - reaction with sulphuric
acid, nitric acid, hydrochloric acid and solutions of iron
(III) chloride, iron(II) sulphate, lead nitrate, zinc nitrate
and copper sulphate.
 Learning Objectives
1. Introduction
2. Occurrence
3. Preparation of Ammonia (General &
Laboratory Methods)
4. Preparation of Aqueous Ammonia [Haber’s
Process]
5. Properties of NH3 [Physical & Chemical]
6. Uses
7. Tests for NH3
1. Introduction
 2. OCCURRENCE

Free state: Ammonia is present in small amounts in

air and in traces in natural water.
 2. OCCURRENCE

Free state: Ammonia is present in small amounts in

air and in traces in natural water.
Note: The pungent smell which one
encounters near a decaying heap of organic
matter or a toilet is due to ammonia.
It is produced due to bacterial decomposition
of urea (NH2CONH2), present in the urine.

CO (NH2)2 + 2H2O → 2NH3 + H2O +

CO2
Forms of ammonia:
Ammonia is used commonly in the following forms

(i) Gaseous ammonia (dry ammonia gas)

(ii) Liquid ammonia. When dry ammonia is liquefied by

applying high pressure it is called liquid ammonia.

(iii) Liquor ammonia fortis is a saturated solution of

ammonia in water. It is called 880 ammonia. It has a
relative density of 0.880. It is stored in tightly stoppered
bottles in a cold place.

(iv) Laboratory bench reagent : Dilute solution of liquor

ammonia is used as a laboratory reagent.
PREPARATION OF AMMONIA GAS:
General methods of preparation: Ammonia gas can be
prepared by warming an ammonium salt with caustic
alkali, such as slaked lime or caustic soda or caustic
potash.
 Laboratory preparation
Reactants: Ammonium chloride
(NH4Cl) and calcium hydroxide
[Ca(OH)2]. (Excess of calcium
hydroxide is mixed well with
ammonium chloride).
Reaction:

2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3.

Procedure:
Precautions: The flask is tilted in
such a way that the water formed in
the reaction does not trickle back
into the heated flask and thus break it.

Drying of ammonia gas: In order to

get dry ammonia, the gas is passed
through a drying tower containing
lumps of quicklime (CaO).
Unsuitability of other drying agents: Other
drying agents like conc. sulphuric acid,
phosphorous pentoxide and anhydrous
calcium chloride are not used, as ammonia
being basic, reacts with them.
Collection:

Ammonia gas is collected in inverted gas

jars by the downward displacement of air
because it is:
(i) lighter than air (V.D. of NH3 8.5; that of air,
14.4),
(ii) highly soluble in water and therefore, it
cannot be collected over water.
Note:
1. Higher ratio by weight of the alkali is used it
may counteract the loss by sublimation of NH4Cl.
2. Calcium hydroxide is used, as it is cheap and
not deliquescent like other alkalies.
3. Though all ammonium salts, on heating with
alkalies give NH3, yet NH4NO3 (explosive in nature)
and NH4NO2 on warming with alkalies do not
produce ammonia because they decompose on
heating.
(2) From metal nitrides
Ammonia can also be obtained by the action
of warm water on nitrides of metals like
magnesium or Aluminium. (This method is
costly)
Procedure:
REPARATION OF AQUEOUS AMMONIA
MANUFACTURE OF AMMONIA
(HABER'S PROCESS)
Reactants: Nitrogen and hydrogen in the ratio of
1 : 3 by volume.

Sources of reactants:
Nitrogen gas is obtained by fractional
distillation of liquid air.

Hydrogen gas is obtained from water gas

(Bosch process) or from natural gas.

Liquid air is air that has been cooled to very low temperatures
(cryogenic temperatures), so that it has condensed into a pale
blue mobile liquid.
Reaction:

Favourable conditions:

Temperature: Optimum temperature is 450-500 °C.

Pressure: Above 200 atm.

Catalyst: Finely divided iron.

Promoter: Traces of molybdenum or Al203.

Rate of conversion: About 15% of the reacting
gases get converted to ammonia.

Recovery of ammonia: Ammonia is separated

from the unreacted nitrogen and hydrogen by:

1. Liquefaction — Ammonia is liquified easily

as compared to nitrogen and hydrogen.

2. Absorbing in water because NH3 is highly

soluble in water, while N2 and H2 are very
slightly soluble.
Note:
(i) The reaction is exothermic, hence low temperature will
favour the synthesis. However, at low temperature, the
reaction proceeds slowly. In practice, the optimum
temperature has been found to be in the range of 450°C to
500°C.

(ii) Four volumes of reactants produce two volumes of

product, hence high pressure favours the formation of
ammonia. The optimum pressure is found to be 200 to 900
atm. Practically, a pressure of about 250 atm. is used. ,

(iii) Catalyst and promoter : The speed of the reaction can

be improved by using a catalyst, which is finely divided
iron, obtained by the reduction of iron oxide. A promoter
molybdenum or Al203 is used to increase the efficiency of
the catalyst.
PHYSICAL PROPERTIES OF AMMONIA
1. Colour: Colourless.

2. Odour: Strong, pungent choking smell.

3. Taste: Slightly bitter (alkaline) taste.

4. Physiological: Non-poisonous. action If

inhaled, affects the respiratory system and
brings tears to eyes. It is a powerful heart
stimulant and may cause death when inhaled
in large quantities.
PHYSICAL PROPERTIES OF AMMONIA
5. Density: Vapour density = 8.5 [Lighter than
air]

6. Nature: Alkaline nature.

7. Liquefaction: Easily liquefied at 10°C by

compressing it at 6 atm. pressure.

8. Boiling point: Liquid ammonia boils at -

33.5°C.
PHYSICAL PROPERTIES OF AMMONIA
9. Freezing point: Solid NH3 melts at -77.7°C.

10. Solubility: Highly soluble in water, 1 vol.

of water dissolves about 702 vols. of
ammonia at 20°C and 1 atm. pressure

FOUNTAIN EXPERIMENT

To demonstrate the high solubility of

ammonia gas in water.
Apparatus :
1. A round bottomed flask filled with ammonia
gas.
2. Mouth of the flask is fitted with a rubber
stopper with two holes, one for jet tube and the
other for a dropper containing water.
3. A trough containing red litmus solution.
4. A retort stand is used to fix the round
bottomed flask in inverted position as shown
in Figure
Note:
A bottle of liquor ammonia should be
opened very carefully, only after
cooling it in ice or cold water. There
is high pressure inside the bottle of
ammonia and on cooling, the
pressure drops. This prevents
sudden flushing out of the gas.
CHEMICAL PROPERTIES OF AMMONIA

1. Thermal dissociation: Ammonia gas

dissociates into nitrogen and hydrogen at
high temperature or by electric sparks.
CHEMICAL PROPERTIES OF AMMONIA
2. Basic properties: Dry ammonia is a
covalent molecule. So, it is neutral even in
liquefied form. Its aqueous solution is a
weak base, the basicity is due to a lone pair
of electrons on its nitrogen atom.
CHEMICAL PROPERTIES OF AMMONIA

2. Basic properties: An aqueous solution of

ammonia [NH4OH] is a weak base. It
dissociates partially to give hydroxyl ions.
The alkaline behaviour is due to the
hydroxyl ions [OH-]
CHEMICAL PROPERTIES OF AMMONIA

2. Basic properties: An aqueous solution of

ammonia [NH4OH] is a weak base. It
dissociates partially to give hydroxyl ions.
The alkaline behaviour is due to the
hydroxyl ions [OH-]
CHEMICAL PROPERTIES OF AMMONIA
Action on indicators

Change in colour
Indicator
Original To

Moist litmus Red Blue

Methyl orange Orange Yellow

Phenolphthalein Colourless Pink

CHEMICAL PROPERTIES OF AMMONIA
3. Burning of ammonia in oxygen: Ammonia
is not a supporter of combustion. It
extinguishes a burning splint and does not
burn in air. It burns in oxygen with
yellowish green flame.
Experiment: Burning of ammonia in oxygen

Mixture of ammonia and oxygen is explosive and

therefore dangerous.
4. Catalytic oxidation of ammonia: In
the presence of platinum at 800°C,
ammonia reacts with oxygen to give
nitric oxide and water vapour.
Procedure : Pass dry ammonia gas
and oxygen gas through inlets over
heated platinum placed in the
combustion tube, which in the heated
state emits a reddish glow.
Procedure:
Observations: (i) Reddish brown vapours of
nitrogen dioxide [NO2] are seen in the flask
due to the oxidation of nitric oxide [NO].

2NO + O2 → 2NO2

(ii) The platinum [catalyst] continues to glow

even after the heating is discontinued since
the catalytic oxidation of ammonia is an
exothermic reaction.
5. Ammonia as a reducing agent:
(i) Reduction of metallic oxides Ammonia
reduces heated metallic oxides to give
metals, water vapour and nitrogen.

Procedure: Pass ammonia gas over heated

copper oxide in a hard glass tube.

Reaction:
Observation: The black copper oxide is
reduced to reddish brown copper.

Similarly, Ammonia reduces heated yellow

lead monoxide to greyish metallic lead.
Collection of gas:

Nitrogen is collected over water in a gas jar.

5. Ammonia as a reducing agent:
(ii) Reduction of chlorine to hydrogen
chloride When chlorine reacts with ammonia,
it is reduced to HCl, which further combines
with excess of ammonia and forms NH4Cl.
5. Ammonia as a reducing agent:
(ii) Reduction of chlorine to hydrogen
chloride When chlorine reacts with ammonia,
it is reduced to HCl, which further combines
with excess of ammonia and forms NH4Cl.
Observation: The yellowish-green colour of
chlorine disappears and white fumes of
ammonium chloride are formed.
(b) When chlorine is in excess, then the
products are hydrogen chloride and yellow
coloured highly explosive liquid nitrogen
trichloride.
NH3 + 3Cl2 → 3HCl + NCl3
 These reactions show that:

• Chlorine has a great affinity for

hydrogen.

• Ammonia is a reducing agent

6. Reaction with acids:
Ammonia being a weak base accepts
protons [hydrogen ions] to form ammonium
ions.
It reacts with acids to form ammonium salts.
 Note: Ammonium nitrate and
ammonium chloride both show
thermal dissociation reaction.
 AQUEOUS SOLUTION OF AMMONIA
Ammonia is dissolved in water to form its aqueous
solution (ammonium hydroxide). NH3 + H2O —> NH4OH
Ammonium hydroxide reacts with acids to form salt and
water.
7. Reaction of aqueous solution of ammonia
with soluble metal salts:

Ammonium hydroxide reacts with soluble salts of metals

to give insoluble precipitates of their respective metallic
hydroxides, (except sodium and potassium).

This behaviour is similar to NaOH solution and KOH

solution.

The precipitates formed by different metallic hydroxides

differ in colour and solubility. Hence, ammonium
hydroxide is used in qualitative analysis for identifying
cations.
 TESTS FOR AMMONIA GAS AND
AMMONIUM ION
Ammonia gas can easily be recognised by the following
characteristics :
(1) It has a sharp characteristic odour.
(2) It turns
• moist red litmus blue,
• moist turmeric paper brown
• phenolphthalein solution pink.
(3) It gives dense white fumes with conc. hydrochloric
acid.
NH3 + HCl —> NH4Cl
 TESTS FOR AMMONIA GAS AND
AMMONIUM ION

(4) When NH3 gas is passed through copper sulphate

solution blue precipitate is formed which changes to
deep blue solution on passing the gas in excess.

(5)All ammonium salts generally produce ammonia gas

when warmed with alkali like sodium hydroxide.

(6) Ammonium salt gives brown colour or precipitates

with Nessler's solution K2HgI4 (a slightly alkaline
solution of potassium mercuric iodide made by adding
KOH).
 USES OF AMMONIA
1. Liquid ammonia is used as a refrigerant in
ice plants.
Advantages of Ammonia as refrigerant:
(i)Ammonia is environmentally compatible. It does not
deplete ozone layer and does not contribute towards the
global warming.

(ii) It has superior thermodynamic qualities as a result

ammonia refrigeration systems use less electricity.

(iii) Ammonia has a recognizable odour and so leaks are

not likely to escape.
 USES OF AMMONIA
2. Ammonia solution is used as an important
laboratory reagent in qualitative analysis as
it gives characteristic coloured metallic
hydroxide precipitates.
3. Aqueous NH3 emulsifies or dissolves fats,
grease, etc. so it is used:
(i) to remove grease and perspiration stains
from clothes,
(ii) for cleaning tiles, windows, etc.
 USES OF AMMONIA
4. Ammonia is used in the manufacture of :
(a) nitrogenous fertilisers like ammonium
sulphate, diammonium hydrogen phosphate,
ammonium nitrate and urea.
Ammonia reacts with carbon dioxide at
150°C and 150 atm. pressure to give urea
which is a valuable nitrogenous fertiliser.
 USES OF AMMONIA
4. Ammonia is used in the manufacture of :
(b) explosives like ammonium nitrate.
Ammonium nitrate decomposes explosively
leaving no residue behind
 USES OF AMMONIA
4. Ammonia is used in the manufacture of :
(c) other ammonium salts such as
ammonium carbonate (used as smelling salt
for reviving a fainted person), ammonium
chloride — used in dry cells and in the
preparation of nitrogen gas.
 USES OF AMMONIA
4. Ammonia is used in the manufacture of :

(d) nylon and rayon, and sodium cyanamide, plastics,

dyes, organic chemicals, explosives and wood pulp.

(e) sodium carbonate by Solvay process. This process

involves the interaction of ammonia, carbon dioxide, and
sodium chloride in water solution resulting in the
precipitation of sodium hydrogen carbonate.

NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl

The sodium hydrogen carbonate is separated and

ignited to obtain sodium carbonate.
2NaHCO3 (𝚫)→ Na2CO3 + H2O + CO2