Question

Name the metal that gets a green coating when exposed to air.

Answer 1

Metals, when exposed to air, react with oxygen and hence get oxidized. This is why the colour of the metals gets changed.

The green coating is observed in the case of Copper (Cu) when it is exposed to moist air (a mixture of Carbon dioxide, Water, and Oxygen). This happens due to corrosion. The chemical reaction is given below:

$$\begin{gathered} \mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to \mathrm{Cu}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+{\mathrm{CuCO}}_3\left(\mathrm{s}\right) \\ \mathrm{Copper}\mathrm{Water}\mathrm{Carbon}\mathrm{Oxygen}\mathrm{Copper}\mathrm{Copper} \\ \mathrm{dioxide}\mathrm{hydroxide}\mathrm{carbonate} \end{gathered}$$

The mixture of Copper hydroxide and Copper carbonate displays a green coating that gets deposited on the surface.

Thus, the metal that gets a green coating when exposed to air is Copper (Cu).