Question

Differentiate between:
(i) Action on indicators or dry ammonia gas and aqueous ammonia.
(ii) Reaction of excess ammonia with chlorine and NH₃ with excess chlorine.
(iii) Aqueous ferrous and ferric sulphate solution.

Answer 1

(i) Dry ammonia gas is a polar molecule and is neutral to indicators. As a result, it does not have any action on indicators. Aqueous ammonia is alkaline in nature. Therefore, it causes a change in the colour of the indicators. Aqueous ammonia turns litmus from red to blue, methyl orange from orange to yellow and phenolphthalein from colourless to deep pink.

(ii) When excess ammonia reacts with chlorine, ammonium chloride is formed and nitrogen gas is released. The yellowish colour of chlorine disappears slowly and white-coloured ammonium chloride is observed. The reaction is: $8{\mathrm{NH}}_3\left(\mathrm{excess}\right)+3{\mathrm{Cl}}_2\to {\mathrm{N}}_2+6{\mathrm{NH}}_4\mathrm{Cl}$
In case of a reaction between excess chlorine and ammonia, nitrogen trichloride, a yellow-coloured explosive liquid, is formed. The reaction is:
${\mathrm{NH}}_3+3{\mathrm{Cl}}_2\left(\mathrm{excess}\right)\to {\mathrm{NCl}}_3+3\mathrm{HCl}$

(iii) Aqueous ferrous sulphate solution contains iron in Fe²⁺ state. As a result, its reaction with ammonia solution leads to the formation of a dirty green Fe(OH)₂ precipitate. In case of ferric sulphate solution, iron is in Fe³⁺ state. Its reaction with ammonia solution leads to the formation of the reddish brown Fe(OH)_3.