Question

On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black) oxygen gas and a brown gas $\mathrm{X}$ is formed.

(a) Write a balanced chemical equation of the reaction

(b) Identify the brown gas $\mathrm{X}$ evolved

(c) Identify the type of reaction

(d) What could be the pH range of the aqueous solution of the gas $\mathrm{X}$?

Answer 1

Heating of Copper (II) nitrate:

• The chemical reaction in which one reactant breaks down into two or more products is known as a decomposition reaction($\mathrm{AB}=\mathrm{A}+\mathrm{B}$).
• The heating of Copper (II) nitrate, results in the loss of a water molecule and anhydrous Copper (II) nitrate is formed.
• On further heating it gives a black residue of Copper oxide, a brown colour Nitrogen dioxide gas, and colorless gas.
• The balanced chemical equation of the reaction is,

$\underset{\mathrm{Copper}\left(\mathrm{II}\right)\mathrm{nitrate}}{2\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{s}\right)}\to \underset{\mathrm{Copper}}{2\mathrm{CuO}\left(\mathrm{s}\right)}+\underset{\mathrm{Nitrogen}\mathrm{dioxide}}{4{\mathrm{NO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}$

• Therefore, the brown gas $\mathrm{X}$ is formed is Nitrogen dioxide respectively.
• Since Nitrogen dioxide is acidic, the pH range of Nitrogen dioxide is less than 7.
• Here, the Copper (II) decomposes to form copper oxide, nitrogen dioxide gas, and oxygen gas as products, therefore, this is a decomposition reaction.