Question

Why ammonia cannot be dried by passing over conc.sulphuric acid and over anhydrous calcium chloride ?

Answer 1

Ammonia cannot be dried by passing over conc. sulphuric acid because ammonia gas reacts chemically with conc. sulphuric acid to form ammonium sulphate.
2NH3 + H2SO4 (conc.) -- (NH4)2SO4.

With anhydrous calcium chloride
it is because ammonia gas forms an addition campound with anhydrous calcium chloride.
8NH3+ CaCl2 -- CaCl2.8NH3 (Additional compound )

Answer 2

Ammonia is a colorless, poisonous gas with a pungent odor. It occurs naturally, primarily as a result of anaerobic decay of plant and animal matter, and has also been detected in space. Some plants, primarily legumes, "fix" atmospheric nitrogen to produce ammonia in collaboration with rhizobia bacteria.

a) Ammonia is basic. So, it reacts with sulphuric acid to form ammonium sulphate so it cannot be dried up using sulphuric acid. The reaction is as follows,

$2NH_{3} + H_{2}SO_{4}$ → $(NH_{4})_{2}SO_{4}$

b) When water is absorbed by calcium chloride, it undergoes hydrolysis to give hydrochloric acid.

$CaCl_{2} + 2H_{2}O$ → $Ca(OH)_{2} + 2HCl$

Since ammonia is basic, it is neutralized by HCl to give salt,

$NH_{3} + HCl$ → $NH_{4}Cl$.

Hence ammonia is dried over a basic oxide, quick line.

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