Question

Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why?

Answer 1

Zinc is more reactive than hydrogen because it is positioned above hydrogen in the metal activity series, whereas copper is below hydrogen.

As a result, zinc interacts with dilute hydrochloric acid $\mathrm{HCl}$ but copper does not.

Zinc reaction with dilute hydrochloric acid:

• Zinc is more reactive than hydrogen, it reacts with hydrochloric acid to release hydrogen gas and hence displace it.
• Zinc quickly interacts with acid to form hydrogen bubbles.
• It is a single displacement reaction in which hydrogen is replaced by zinc metal, resulting in the formation of hydrogen gas and the salt zinc chloride.
• Because the process is exothermic, it generates heat.
• $$\begin{gathered} \mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{HCl}\left(\mathrm{l}\right)\to {\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{ZnCl}}_2\left(\mathrm{s}\right)+\mathrm{heat} \\ \mathrm{Zinc}+\mathrm{Hydrogen}\mathrm{chloride}\to \mathrm{Hydrogen}+\mathrm{Zinc}\mathrm{chloride}+\mathrm{Heat} \end{gathered}$$

Copper reaction with dilute hydrochloric acid:

• Copper is less reactive than hydrogen and thus cannot substitute it.