Question

Select the correct word from the list given in the bracket for each of the following statements.

A nitrate which leaves black residue on heating is_________$(\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2/\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2)$.

Answer 1

1. A nitrate which leaves black residue on heating is $\mathbf{Cu}{\mathbf{\left(}{\mathbf{NO}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}$.
2. The decomposition reaction of Copper nitrate is shown below.
   $\underset{(\mathrm{Copper}\mathrm{nitrate})}{2\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{s}\right)}\stackrel{∆}{\to }\underset{(\mathrm{Copper}\mathrm{oxide})}{2\mathrm{CuO}\left(\mathrm{s}\right)}+\underset{(\mathrm{Nitrogen}\mathrm{dioxide})}{4{\mathrm{NO}}_2\left(\mathrm{g}\right)}+{\mathrm{O}}_2\left(\mathrm{g}\right)$
3. Copper nitrate is present in blue-green crystal form.
4. On heating, the blue-green crystals of Copper nitrate changes to black Copper oxide by liberating reddish brown Nitrogen gas and Oxygen.
5. Hence, $\mathbf{Cu}{\mathbf{\left(}{\mathbf{NO}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}$leaves a black residue on heating.