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Chemistry

State relevant observation for the following:

(a) Ammonia gas is passed over heated copper (II) oxide.

(b) In the absence of catalyst, ammonia is burnt in an atmosphere of oxygen.

(c) Ammonium hydroxide is first added in a small quantity and then in excess to a solution of copper sulphate.

(d) Water is added to the product formed, when Al is burnt in a jar of nitrogen gas.

(e) Excess of chlorine gas is reacted with ammonia gas.

(f) Calcium hydroxide is heated with ammonium chloride crystals.

Ammonia

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Answer

(a) Black copper [II] oxide is reduced to brown copper.

2NH3 + 3CuO ⟶ 3Cu + 3H2O + N2 [g]

(b) Green or greenish yellow flame is seen when ammonia gas is burnt in an atmosphere of oxygen. The reaction of combustion of Ammonia is:

4NH3 + 3O2 ⟶ 2N2 + 6H2O

(c) Ammonium hydroxide if first added in small quantity and then in excess to a solution of copper sulphate, a pale blue ppt. of copper hydroxide is formed which dissolves in excess of ammonium hydroxide forming a soluble complex salt.

CuSO4 + 2NH4OH ⟶ (NH4)2SO4 + Cu(OH)2

Cu(OH)2 + (NH4)2SO4 + 2NH4OH ⟶ [Cu(NH3)4]SO4 + 4H2O

(d) When Al metal is burnt in a jar of nitrogen gas, its nitride i.e., AlN is formed. When warm water is added to AlN, it undergoes hydrolysis and is decomposed by warm water to give pungent smelling ammonia gas. The corresponding insoluble metal hydroxide (i.e., Al(OH)3) is precipitated out. The reactions are shown below:

2Al + N2 ⟶ 2AlN

AlN + 3H2O ⟶ Al(OH)3 + NH3 [g]

(e) Colourless ammonia gas reacts with greenish yellow excess chlorine giving a yellow explosive liquid (Nitrogen trichloride).

NH3 + 3Cl2 [excess] ⟶ 3HCl + NCl3

(f) Pungent smelling gas (ammonia) is given out.

2NH4Cl + Ca(OH)2 ⟶ CaCl2 + 2H2O + 2NH3

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