Question

A white solid A when heated with sodium hydroxide solution gives a pungent gas B which turns red litmus paper blue. The solid when dissolved in dilute nitric acid is treated with Silver nitrate solution to give white precipitate C, which is soluble in ammonia.

(A) What are the substance A, B, and C?

(B) Write an equation from the direct changes taking place in the experiments.

Answer 1

Part: 1: Reaction of Ammonium chloride and Sodium hydroxide:

• Ammonium chloride $\left({\mathrm{NH}}_4\mathrm{Cl}\right)$is a white crystalline solid that is soluble in water. On heating with sodium hydroxide $\left(\mathrm{NaOH}\right)$, it produces ammonia gas $\left({\mathrm{NH}}_3\right)$ which is a colorless gas having a pungent smell. Thus, Ammonia gas turns red litmus paper blue because it has a pH of 11.6.

Part: 2: Reaction of Ammonium chloride and Silver nitrate:

• When Ammonium chloride $\left({\mathrm{NH}}_4\mathrm{Cl}\right)$is a white crystalline solid that reacts with silver nitrate $\left({\mathrm{AgNO}}_3\right)$ in the presence of dilute Nitric acid $(\mathrm{Dil}.{\mathrm{HNO}}_3)$ then it leads to the formation of Silver chloride $\left(\mathrm{AgCl}\right)$and Ammonium nitrate (${\mathrm{NH}}_4{\mathrm{NO}}_3$).

Part: 3: Reaction of Silver chloride and ammonia:

• AgCl is soluble in Ammonia because it forms complexes$\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\right]\mathrm{Cl}$. The formation of the complex ion ${\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\right]}^{2+}$ makes it behave like an ion, therefore, making it soluble.

(A) Thus, Compound A is Ammonium chloride, B is ammonia gas and C is Silver chloride.

(B) Chemical equations from the direct changes taking place in the experiments are as follows.

$\underset{\mathrm{Ammonium}\mathrm{chloride}}{{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\mathrm{NaOH}\left(\mathrm{s}\right)}\to \underset{\mathrm{Sodium}\mathrm{chloride}}{\mathrm{NaCl}\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonia}}{{\mathrm{NH}}_3\left(\mathrm{g}\right)}$

$\underset{\mathrm{Ammonium}\mathrm{chloride}}{{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{s}\right)}+\underset{\mathrm{Silver}\mathrm{nitrate}}{{\mathrm{AgNO}}_3\left(\mathrm{s}\right)}\stackrel{\mathrm{Dil}.{\mathrm{HNO}}_3}{\to }\underset{\mathrm{Silver}\mathrm{chloride}}{\mathrm{AgCl}\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonium}\mathrm{nitrate}}{{\mathrm{NH}}_4{\mathrm{NO}}_3\left(\mathrm{s}\right)}$

$\underset{\mathrm{Silver}\mathrm{chloride}}{\mathrm{AgCl}\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonia}}{{\mathrm{NH}}_3\left(\mathrm{g}\right)}\to \underset{\mathrm{Diammine}\mathrm{Silver}\left(\mathrm{I}\right)\mathrm{Chloride}}{\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\right]\mathrm{Cl}}$