Question

On heating copper powder in air the surface of copper powder becomes coated with black CuO . How can this black coating be converted into brown copper? Write a chemical equation for the reaction that occurs during the colour change.

Answer 1

• On heating copper powder in air, it becomes coated with black copper (ll) oxide since oxygen is added to copper and copper oxide is formed.
• If hydrogen gas is passed over this heated material (CuO), the reverse action takes place i.e. copper regains its brown colour.​
• The reaction for the formation of black copper oxide is as follows:

$2Cu+H_{2}O⟶2CuO$

• The reaction for the formation of brown copper is as follows:​

$CuO+H_2⟶Cu+H_{2}O$