(a) Why are metals not generally found in their free state ?
(b) If a strip of aluminium with scratched surface is dipped in an aqueous solution of copper sulphate for little time, the surface of the strip becomes brownish. What is the reason for this ? Write the balanced chemical equation for the reaction.

Explanation

(a) Metals in general are of reactive nature. Due to the high temperature prevailing below the surface of the earth, they generally exist in combined states with other elements (metals and non-metals).
(b) Aluminium displaces copper from the aqueous copper sulphate solution since it is placed above copper in the activity series. Copper forms a brownish coating over the surface of the metal.
`2Al(s) + 3CuSO_(4)(aq) rarr Al_(2)(SO_(4))_(3)(aq) + 3Cu(s)`