Question

Compound A is a white crystalline solid. When heated it leaves a yellow residue of compound B, a reddish brown gas C, and another gas D. When compound A is dissolved in water and treated with dilute hydrochloric acid, a white precipitate E is formed and dissolves on boiling. Identify A, B, C, D, and E and explain the reaction.

Answer 1

Part: 1: Decomposition reaction of Lead nitrate:

• When Lead nitrate $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2$ which is a white crystalline solid decomposes on heating it gives Lead oxide which is present in a yellow powder-like texture, Nitrogen dioxide (Reddish brown gas), and Oxygen gas.
• The chemical reaction is as follows.

$\underset{\mathrm{Lead}\mathrm{nitate}}{\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2(\mathrm{s}})\stackrel{∆}{\to }\underset{\mathrm{Lead}\mathrm{oxide}}{2\mathrm{PbO}\left(\mathrm{s}\right)}+\underset{\mathrm{Nitrogen}\mathrm{dioxide}}{{\mathrm{NO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}$

Part: 2: Reaction of lead nitrate and water when treated with dilute hydrochloric acid:

• When lead nitrate is dissolved in water and treated with dilute hydrochloric acid it undergoes a chemical change and forms Lead chloride $\left({\mathrm{PbCl}}_2\right)$ which is a white precipitate and Nitric acid $\left({\mathrm{HNO}}_3\right)$.
• The chemical reaction is as follows.

$\underset{\mathrm{Lead}\mathrm{nitrate}}{\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Lead}\mathrm{chloride}}{{\mathrm{PbCl}}_2\left(\mathrm{ppt}\right)}+\underset{\mathrm{Nitric}\mathrm{acid}}{2{\mathrm{HNO}}_3\left(\mathrm{aq}\right)}$

Thus, compound A is Lead nitrate, B is Nitrogen dioxide $\left({\mathrm{NO}}_2\right)$ which is reddish brown gas, C is Lead oxide $\left(\mathrm{PbO}\right)$ and D is Oxygen gas $\left({\mathrm{O}}_2\right)$.

Further in the chemical reaction in part-2, precipitate which is formed is compound E i.e., Lead chloride.