Question

______ is the green colour coating that forms on copper when it is left open.

• A. Copper sulphate
• B. Copper chloride
• C. Copper carbonate
• D. Copper nitrate

Answer 1

The correct option is C Copper carbonate

Copper gains a green coating of basic copper carbonate on its surface when exposed to the atmosphere due to its reaction with oxygen, carbon dioxide and moisture. The reactions that takes place are given below:
$4\mathrm{Cu}\left(s\right)+O_2\left(g\right)\to 2{\mathrm{Cu}}_{2}O\left(s\right)$$2{\mathrm{Cu}}_{2}O\left(s\right)+O_2\left(g\right)\to 4\mathrm{CuO}\left(s\right)$$2\mathrm{CuO}\left(s\right)+{\mathrm{CO}}_2\left(g\right)+H_{2}O\left(l\right)\to {\mathrm{CuCO}}_3\left(s\right)+\mathrm{Cu}\left(\mathrm{OH}{)}_2\right(\mathrm{aq})$