Ammonia

Ammonia is a compound of hydrogen and nitrogen (NH3).

Laboratory preparation of ammonia

It is prepared in the laboratory by heating ammonium chloride with calcium hydroxide.

Laboratory preparation of ammonia

NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3

→The round bottomed flask is tilted (kept in an inclined position) to prevent any condensed water from running back into the hot flask, which would make the flask crack.

→ Calcium oxide (CaO) is used as a drying agent for the gas because other drying agents react with ammonia.

2NH3 + H2SO4 → (NH4)2SO4
6NH3 + P2O5 + 3H2O → 2(NH4)3PO4
4NH3 + CaCl2 → CaCl2.4NH3

→ Ammonia gas is collected by downward displacement of air because it is less dense than air.

→Ammonia cannot be collected by downward displacement of water, because it is extremely soluble in water.

Another method of preparing ammonia is by heating magnesium nitride (Mg3N2) with water.
Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3

PROPERTIES OF AMMONIA

(a) Physical properties of ammonia

  1. Ammonia is a colourless gas with a pungent choking smell.
  2. Ammonia turns wet red litmus paper blue showing that the gas in alkaline in nature.
  3. Ammonia is less dense than air.
  4. Ammonia is highly soluble in water. This can be illustrated by using the Fountain Experiment.

(b) Chemical properties of ammonia

  1. Reaction with water.
    Ammonia gas dissolves in water to form ammonia solution.
    NH3(g) + H2O(l) → NH4+(aq) + OH-(aq).
  2. Reducing property of ammonia
    Ammonia reduces copper (II) oxide (CuO) and lead (II) oxide (PbO) to the respective metals and oxidizes itself to nitrogen gas.
    2NH3 (g)+ 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(l)
    2NH3(g) + PbO (s)→ N2(g) + 3Pb(s) + 3H2O(l)
  3. Reaction with concentrated hydrochloric acid
    NH3 + HCl → NH4Cl (dense white fumes)
  4. Reaction with oxygen
    (a)On burning:
    4NH3 + 3O2 → 2N2 + 6H2O
    (b) Under platinum catalyst
    4NH3 + 5O2 → 4NO + 6H2O
    (Further oxidation of oxide above, reddish brown gas evolves
    NO(g) + O2 (g) → NO2(g))
  5. Reaction with chlorine
    2NH3 + 3Cl2 → N2 + 6HCl
    In excess of NH3
    8NH3 + 3Cl2 → 6NH4Cl + N2

    Test for ammonia gas

    It form a dense white fumes with concentrated hydrochloric acid or hydrogen chloride gas.

    Uses of ammonia

    1. It is used in the manufacture of nitric acid.
    2. It is used in the manufacture of nitrogeneous fertilizers eg. ammonium sulphate and urea
    3. It is used in the softening of hard water.
    4. As refrigerant
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