Question

Give reason why the blue colour of copper sulphate solution is discharged slowly when an iron rod is dipped in it.

Given: \[\ce{E^{\circ}_{{Cu^{2+}/{Cu}}} = 0.34 V}\], \[\ce{E^{\circ}_{{Fe^{2+}/{Fe}}} = -0.44 V}\].

Answer 1

The standard reduction potential of Cu²⁺/Cu is +0.34 V, while that of Fe²⁺/Fe is –0.44 V. Since copper has a higher reduction potential than iron, it has a greater tendency to get reduced. When an iron rod is dipped into a CuSO₄ solution, a redox reaction occurs:

\[\ce{Fe_{(s)} + Cu{^{2+}_{(aq)}} -> Fe{^{2+}_{(aq)}} + Cu_{(s)}}\]

Iron is oxidised to Fe²⁺ and Cu²⁺ is reduced to copper metal, which deposits on the rod. As the reaction proceeds, the concentration of blue-coloured Cu²⁺ ions decreases, so the blue colour of CuSO₄ solution fades slowly.