Question

Write down balance equation for the following:

1. action of concentrated nitric acid on copper.
2. action of heat on sodium nitrate.

Answer 1

1. When concentrated nitric acid is treated with copper the copper gets oxidized. The pinkish red metal dissolves in nitric acid to give a blue coloured solution of copper nitrate and a reddish brown coloured gas of nitrogen dioxide.

$\underset{\mathrm{copper}}{\underset{}{\mathrm{Cu}}\left(s\right)}+\underset{\mathrm{conc}\mathrm{nitric}\mathrm{acid}}{\underset{}{4{\mathrm{HNO}}_3\left(\mathrm{l}\right)}}\to \underset{\mathrm{copper}\left(\mathrm{III}\right)\mathrm{nitrate}}{\underset{}{\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{s}\right)}}+\underset{\mathrm{nitrogen}\mathrm{dioxide}}{\underset{}{2{\mathrm{NO}}_2\left(\mathrm{g}\right)}}+\underset{\mathrm{water}}{\underset{}{2{\mathrm{H}}_2\mathrm{O}}}$

b). Sodium nitrate on heating decomposes to produce sodium nitrite and colourless and odourless oxygen gas
.$$\begin{gathered} \underset{}{\underset{}{2{\mathrm{NaNO}}_3\left(\mathrm{s}\right)}}\stackrel{∆}{\to }\underset{}{\underset{}{2{\mathrm{NaNO}}_2\left(\mathrm{s}\right)}}+{\mathrm{O}}_2\left(\mathrm{g}\right)\uparrow \\ \mathrm{sodium}\mathrm{sodium}\mathrm{oxygen}\mathrm{gas} \\ \mathrm{nitrate}\mathrm{nitrite} \end{gathered}$$