Question

Question 16
If copper is kept in open air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of
(a) ${\text{CuSO}}_4$
(b) ${\text{CuCO}}_3$
(c) ${\text{Cu(NO}}_3{)}_2$
(d) $\text{CuO}$

Answer 1

Option (d) is correct.
Copper gains a green coating on its surface when exposed to the atmosphere due to its reaction with oxygen, carbon dioxide and moisture present in it. The reactions that takes place are given below:
$4\text{Cu}+{\text{O}}_2⟶2{\text{Cu}}_2\text{O}$
$2{\text{Cu}}_2\text{O}+{\text{O}}_2⟶4\text{CuO}$
$2\text{CuO}+{\text{CO}}_2+{\text{H}}_2\text{O}⟶{\text{CuCO}}_3+{\text{Cu(OH)}}_2$