Question

(a) Name an alloy of copper. State its chemical composition and any one use.
(b) Explain why, when a copper object remains in damp air for a considerable time, a green coating is formed on its surface. What is this process known as?

Answer 1

(a) An alloy of copper is bronze. The constituent elements of bronze are copper and tin.
The composition of bronze is 90 percent copper and 10 percent tin. This alloy of copper is very strong and prevents corrosion.
Bronze is used in the manufacturing of statues, medals, cooking vessels etc.

(b) Copper object, staying in damp air for a long time, reacts with carbon dioxide and moisture (water) in air slowly to form green layer of basic copper carbonate $\left({\mathrm{CuCO}}_3.\mathrm{Cu}(\mathrm{OH}{)}_2\right)$ on the outside area of the object. This process is known as corrosion. Copper is very low in its reactivity; therefore, corrosion of copper also occurs slowly.