Give reasons for the following :
(i) Metals are regarded as electro-positive elements.
(ii) When a piece of copper metal is added to a solution of zinc sulphate, no change takes place, but the blue colour of copper sulphate fades away when a piece of zinc is placed in its solution.
(iii) Articles made of aluminium do not corrode even though aluminium is an active metal.
(i) Metals are regarded as electropositive elements because they lose electrons to form metal cations.
(ii) When a piece of copper metal is added to a solution of zinc sulphate, no change takes place since, copper is less reactive than zinc and hence, will not displace it from zinc sulphate solution.
When some zinc is put into blue copper sulphate solution, the blue colour of the copper sulphate solution fades gradually due to the formation of colourless zinc sulphate and red-brown copper metal is deposited on the zinc strip. The reaction takes place as zinc is more reactive than copper.
(iii) Articles made of aluminium do not corrode even though aluminium is an active metal as a protective layer of aluminium oxide is formed over the aluminium metal.