Question

Give reasons for the following: 

(i) Silver and copper lose their shine when they are exposed to air. Name the substance formed on their surface in each case. 

(ii) Tarnished copper vessels are cleaned with tamarind juice. 

(iii) Aluminium is more reactive than iron yet there is less corrosion of aluminium as compared to iron when both are exposed to air.

Answer 1

(i) These metals get corroded. Silver forms black Ag₂S (silver sulphide) and copper form greenish layer of basic copper carbonate CuCO₃. Cu(OH)₂. 

(ii) Tamarind contains acid which reacts with basic copper carbonate and product gets dissolved and removed from copper vessel. 

(iii) Aluminium forms oxide layer on its surface which does not further react with air.