Question

Ammonia gas is evolved when ammonium salt is heated with Sodium hydroxide solution. Give three ways by which this gas can be detected.

Answer 1

Tests for Ammonia gas:

1.Test with Concentrated$\mathrm{HCl}$ : Ammonia gives white dense fumes of Ammonium chloride(${\mathrm{NH}}_4\mathrm{Cl}$) with Concentrated Hydrochloric acid.

${\mathrm{NH}}_3\left(\mathrm{g}\right)+\mathrm{HCl}\left(\mathrm{l}\right)\to {\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{s}\right)$

2.Test with Nessler's solution: Potassium tetraiodomercurate(II) (${\mathrm{K}}_2{\mathrm{HgI}}_4$) is the Nessler's reagent.

Ammonium salt gives brown color precipitate with Nessler's solution.

3. Test with Copper sulfate solution: Ammonium salt forms a blue precipitate with Copper sulfate solution.

$$\begin{gathered} {\mathrm{CuSO}}_4\left(\mathrm{aq}\right)+2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)\to {\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+\mathrm{Cu}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right) \\ CoppersulfateAmmoniumhydroxideAmmoniumsulfateCopperhydroxide \end{gathered}$$

So presence of ammonia can be tested by using Concentrated Hydrochloric acid, Nessler's reagent and Copper sulfate solution.