JAMB - Chemistry (1978 - No. 32)
If excess zinc is added to a bluish green solution of copper (II) sulphate, and the excess zinc filtered off after completion of reaction, a colourless solution is obtained because
both zinc and copper are metals
the sulphate radical and the zinc ion are divalent
zinc is more electropositive than copper
both zinc and copper form depositive ions in solution
zinc is a reducing agent
Explication
Zinc displaces copper from copper sulphate and generates zinc sulphate solution when added to CuSO\(_4\) solution because zinc is a more reactive metal that displaces less reactive metal from its solution. This implies Zinc is more electropositive than Copper. The colour change shows it.