Question

On the basis of electrochemical series, explain why a coating of copper is deposited on an iron nail when placed in an aqueous solution of copper sulphate.

Answer 1

According to the electrochemical series, iron (Fe) has a lower standard reduction potential (E° = −0.44 V) compared to copper (Cu) (E° = +0.34 V). This means iron is more reactive than copper and can easily lose electrons (i.e., it gets oxidised), whereas copper ions can gain electrons (i.e., get reduced).

When an iron nail is placed in an aqueous solution of copper sulphate (CuSO₄), the following redox reaction occurs:

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

In this reaction, iron displaces copper from the solution by donating electrons to Cu²⁺ ions, reducing them to metallic copper. The copper gets deposited as a reddish-brown coating on the surface of the iron nail.

Thus, based on the electrochemical series, a coating of copper forms on the iron nail because iron is more reactive and displaces copper from its salt solution.