Question

When an ammonium salt is warmed with sodium hydroxide solution, ammonia gas is evolved. State three ways by which you can identify this gas.

Answer 1

Three ways to detect ammonia gas:

1. Ammonia can be recognised by its pungent smell.
2. When moist red litmus paper is held in this gas, it turns blue.
3. It gives a brown precipitate on treatment with Nessler's reagent.

$$\begin{gathered} 2{\mathrm{K}}_2\left[{\mathrm{HgI}}_4\right]+{\mathrm{NH}}_3+4\mathrm{KOH}\to \left[{\mathrm{OHg}}_2{\mathrm{NH}}_2\right]\mathrm{I}+7\mathrm{KI}+2{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Nessler}\text{'}\mathrm{s}\mathrm{reagant}\mathrm{Ammonia}\mathrm{Brown}\mathrm{precipitate} \end{gathered}$$