Question

Name a black metallic oxide that reacts with dilute HCl to give a blue solution.

Answer 1

A black metallic oxide that reacts with dilute HCl to give a blue solution is a Copper oxide($\mathrm{CuO}$). The blue solution which is obtained is Copper chloride(${\mathrm{CuCl}}_2$)

• Copper oxide($\mathrm{CuO}$) reacts with dilute $\mathrm{HCl}$ to give Copper chloride(${\mathrm{CuCl}}_2$) and Water(${\mathrm{H}}_2\mathrm{O}$)
• $\underset{\mathrm{Copper}\mathrm{Oxide}}{\mathrm{CuO}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{Chloride}}{2\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Copper}\mathrm{Chloride}}{{\mathrm{CuCl}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Copper oxide($\mathrm{CuO}$) is black in colour and copper chloride obtained after its reaction with hydrochloric acid is blue in colour.