Ammonia

Ammonia

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Method of preparation: Ammonia

1. By the reaction of water with metal nitride:
Mg₃N₂ (Magnesium nitride + 6H₂O ——-> 3Mg(OH)₂ +2NH₃
ALN (Aluminium nitride) + 3H₂O  ——–> Al(OH)₃+ NH₃

2. By heating ammonium salt with base:
2NH₄Cl + Ca(OH)₂ ——-> CaCl₂ +2NH₃ +2H₂O
2NH₄Cl + PbO    ——-> PbCl₂ + 2NH₃+ H₂O
NH₄Cl + NaOH     ——-> NaCl + NH₃ + H₂O

Lab method :
In laboratory, NH₃ is prepared by heating ammonium chloride with calcium hydroxide. Concentrated H₂SO₄, anhydrous CaCl₂, P₂O₅ cannot be used to dry NH3 because they react chemically with NH3.

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H₂SO₄ (Concentrated) +2NH₃ ———> (NH₄)₂SO₄

CaCl₂ +8NH₃ ———-> CaCl₂.8NH₃

P₂O₅ + 3H₂O +6NH₃          —————–>2 (NH₄)₃PO₄

Manufacture:

It is manufactured by three method:

1) From ammonical liquor:

Ammonical liquor is obtained as a by product when coal gas is manufactured by the destructive distillation of coal. Ammonical liquor contains ammonium salt such as NH₄Cl, (NH₄)₂SO₄, (NH₄)₂S etc. Ammonia is obtained by heating ammonical liquor with slaked lime (Ca(OH)₂ ). Ammonia obtained is either liquefied or dissolved in dilute H2SO4 to get ammonium sulphate which is used as fertilizer.

2NH₄Cl + Ca(OH)₂  ———>CaCl₂ + 2NH₃ + 2H₂O

(NH₄)₂SO₄  + Ca(OH)₂  ———>CaSO₄ + 2NH₃ + 2H₂O

(NH₄)₂S + Ca(OH)₂  ———>CaS + 2NH₃ + 2H₂O

2NH₃ + H₂SO₄ (dilute) ———> (NH₄)₂SO₄

Physical properties:

1. It is colorless, pungent odor gas.

2. Ammonia is highly soluble in H₂O. Its aqueous solution is called ammonium hydroxide.

NH₃ +H₂O ——-> NH₄OH (weak base)

Test of Ammonia :

1. Ammonia has pungent ammonical odor.

2. Its aqueous solution turn red litmus blue.

3. Copper sulphate solution react with excess of NH4OH then blue color soluble complex is obtained.

4. Concentrated HCl gives white fumes of NH₄Cl with NH₃ .

5. It gives orange-brown precipitate with  alkaline solution of K₂[HgI₄] i.e Nessler’s reagent

2K₂[HgI₄] + NaOH + NH₃  ———> NH₂Hg₂I₃ (brown precipitate) + 4 KI +  NaI +H₂O

NH₂Hg₂I₃ is Iodide of million’s base.