Question

When Lead nitrate is heated it decomposes with a cracking sound, a reddish brown gas is liberated and a solid residue is left in the test tube. Write the name and formula of the gas.

Answer 1

1. Decomposition reaction

A decomposition reaction is a type of reaction in which the reactant compound is broken down into more than one smaller compound when exposed to certain conditions.

2. Heating of Lead nitrate

Lead nitrate undergoes a decomposition reaction to give a solid residue named Lead oxide and a reddish-brown gas named Nitrogen dioxide.

The reaction for the decomposition of Lead nitrate $\left[\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\right]$ is given below.

$$\begin{gathered} 2\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)\to 2\mathrm{PbO}\left(\mathrm{s}\right)+4{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2 \\ \left(\mathrm{Lead}\mathrm{nitrate}\right)\left(\mathrm{Lead}\mathrm{oxide}\right)(\mathrm{Nitrogen}(\mathrm{Oxygen}) \\ \mathrm{dioxide}) \end{gathered}$$

Hence, the reddish-brown gas liberated is Nitrogen dioxide and its formula is ${\mathrm{NO}}_2$. The solid residue is Lead oxide $\left(\mathrm{PbO}\right)$.