Thursday, 19 February 2015

9.2 Manufacture of Ammonia and its Salt

Properties of ammonia
■ Properties of ammonia

Colourless, pungent smelling gas which is alkaline in nature.

Dissolves in water to form an aqueous alkaline solution.
NH3(g) + H2O ⇌ NH4+(aq) + OH-(aq)
Ammonia is very soluble in water. Thus, the gas is passed through an inverted filter funnel to prevent the sucking back of water into flask.

Test for ammonia: ammonia gas reacts with hydrogen chloride to form with fumes of ammonium chloride.
NH3(g) + HCl(g) → NH4Cl(g)

Ammonia has basic properties. It reacts with acid to form salts.
2NH3(g) + H2SO4(l) → (NH4)2SO4(aq)
■ Ammonia is a reagent used in qualitative analysis.

It forms insoluble hydroxide of all metals except Na+, K+ salts, when a little ammonia solution is added to the salts.
Cu2+ + 2NH3(g) + H2O(l) → Cu(OH)2(s) + NH4+(aq)
Mg2+ + 2NH3(g) + H2O(l) → Mg(OH)2(s) + NH4+(aq)

Cations like Cu2+ and Zn2+ dissolve when excess ammonia is added to their salt solutions. This is because soluble complex salts are formed.
Cu(OH)2(s) + 4NH3 → (Cu(NH3)4)2+ + 2OH-
Zn(OH)2(s) + 4NH3 → (Zn(NH3)4)2+ + 2OH-
■ This video contains information on the synthesis of ammonia through the Haber process in industry.
■ This video contains information on the uses of ammonia.

Uses of ammonia
■ Uses of ammonia and its compounds in daily life
Nitric acid
Cooling agents
Prevents coagulation of latex
Paint and colouring
Synthetic fabric
Explosives (TNT)
Manufacture of ammonia
■ Production of nitrogen gas

Nitrogen gas is obtained from fractional distillation of liquid.
Reaction between steam and heated coke(carbon): H2O + C → CO + H2
Reaction between steam and natural gas: 2H2O + CH4 → CO2 + 4H2
■ Haber process

Nitrogen and hydrogen are mixed in the ratio of 1 : 3 volumes and passed over iron fillings(catalyst) mixed with aluminium oxide at 450°C – 550°C.

The optimum pressure used in this process is 200 atmospheres.

The animation below shows the production of ammonia through the Haber process.
■ This video shows the manufacturing process of ammonia.

Preparation of ammonia fertiliser in the laboratory
Ammonia fertiliser is a nitrogen fertiliser that supplies nitrogen element to animals and plants during formation of protein.
■ Step in preparing ammonia fertiliser:

Step 1: Ammonia solution + acid → ammonium salt

Step 2: Ammonium salt is evaporated to obtain a saturated ammonium salt solution.

Step 3: The saturated ammonium salt solution is cooled and crystallised to obtain ammonia fertiliser.
■ Examples of ammonia fertiliser :

Ammonia solution + sulphuric acid → ammonium sulphate

Ammonia solution + nitric acid → ammonium nitrate

Ammonia solution + phosphoric acid → ammonium phosphate
Laboratory Activity 9.2.1 : Preparation of ammonium sulphate

⇲ For exercise(objective and subjective), download for free on Android OS.

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