Question

Copper becomes green when exposed to moist air for a long period. This is due to:

• A. the formation of a layer of cupric hydroxide on the surface of copper
• B. the formation of basic copper sulphate layer on the surface of the metal
• C. the formation of a layer of cupric oxide on the surface of copper
• D. the formation of a layer of basic carbonate of copper on the surface of copper

Answer 1

The correct option is D the formation of a layer of basic carbonate of copper on the surface of copper

When a copper vessel is exposed to moist air for a long time it develops a green layer on it surface. Copper corrodes by oxidation in which it reacts with oxygen in the air to form copper oxide .
Copper oxide then combines with carbon dioxide to make copper carbonate ,which gives it a green colour. This process is called corrosion of copper.
The green material is a mixture of copper hydroxide $\left(Cu\right(OH{)}_2)$ and copper carbonate $\left(CuC{O}_3\right)$.The following is the reaction .

$2Cu\left(s\right)+H_{2}O\left(g\right)+C{O}_2+O_2\to Cu(OH{)}_2+CuC{O}_3(s)$
Copper (II) carbonate is a blue-green compound.
Hence, Option B is correct.