Why blue colour of copper sulphate solution gets discharged when zinc rod is dipped in it?
(Given E°(Cu2+, Cu) = 0.34 V and E°(Zn, Zn2+) = 0.76 V)
Since E°(Zn, Zn2+) = −E°(Zn2+,Zn)=−0.76 V is lower than E°(Cu2+, Cu), therefore Zn will lose electrons and copper will accept them.
In other words, the following reaction will occur:
Zn + Cu2+ ⟶ Zn2+ + Cu
Since blue Cu2+ ions are consumed and colour less Zn2+ ions are produced during the above reaction, therefore the colour of CuSO4 solution gets discharged when zinc rod is dipped in it.