Question

State one chemical test between the following pair:

Manganese dioxide and Copper (II) oxide.

Answer 1

Heating with conc. $\mathbf{HCl}$:

When Manganese dioxide $\left({\mathrm{MnO}}_2\right)$is heated with conc. $\mathrm{HCl}$, Chlorine gas is evolved during the reaction.

Balanced chemical equation:-

$\underset{\mathrm{Manganese}\mathrm{dioxide}}{\underbrace{{\mathrm{MnO}}_2\left(\mathrm{s}\right)}}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\underbrace{4\mathrm{HCl}\left(\mathrm{aq}\right)}}\to \underset{\mathrm{Manganese}\mathrm{chloride}}{\underbrace{{\mathrm{MnCl}}_2\left(\mathrm{aq}\right)}}+\underset{\mathrm{water}}{\underbrace{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}+\underset{\mathrm{Chlorine}\mathrm{gas}}{\underbrace{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}}$

• When Copper (II) oxide $\mathbf{\left(}\mathbf{CuO}\mathbf{\right)}$ is heated with conc. $\mathrm{HCl}$, chlorine gas is not evolved during the reaction.

Balanced chemical equation:

$\underset{\mathrm{Copper}\left(\mathrm{II}\right)\mathrm{oxide}}{\underbrace{\mathrm{CuO}\left(\mathrm{s}\right)}}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\underbrace{2\mathrm{HCl}\left(\mathrm{aq}\right)}}\to \underset{\mathrm{Copper}\left(\mathrm{II}\right)\mathrm{chloride}}{\underbrace{{\mathrm{CuCl}}_2\left(\mathrm{aq}\right)}}+\underset{\mathrm{water}}{\underbrace{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}$

In this way, we can distinguish between Manganese dioxide and Copper (II) oxide.