Question

State one appropriate observation for the following:

Copper sulphide is heated with dilute hydrochloric acid.

Answer 1

Copper sulphide reacts with acid:

• From this reaction, we can observe a black-coloured copper sulphite turns blue and hydrogen sulphide gas is liberated.
• When copper sulphide $\left(\mathrm{CuS}\right)$ is heated with dilute hydrochloric acid $\left(\mathrm{HCl}\right)$, they react and form copper chloride $\left({\mathrm{CuCl}}_2\right)$ and release hydrogen sulphide $\left({\mathrm{H}}_2\mathrm{S}\right)$ gas with a rotten egg-like smell.
• Balanced chemical reaction equation:

$\underset{\mathrm{Black}}{\mathrm{CuS}\left(\mathrm{s}\right)}+\mathrm{HCl}\left(\mathrm{aq}\right)\stackrel{}{\to }\underset{\mathrm{Blue}}{{\mathrm{CuCl}}_2\left(\mathrm{aq}\right)}+{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)$

Hence, the reaction produces blue copper chloride and hydrogen sulphide, a rotten egg smell gas.