Question

Write all the observations when an iron nail is dipped in a solution of copper sulphate.

Answer 1

Displacement reactions

Reactions in which a more reactive metal displaces a less reactive metal from its salt solution are called displacement reactions. The reactivity series is used to determine the products of a displacement reaction. It arranges the metals in the order of their reactivity with dilute acids.

Displacement reactions occur only when a more reactive metal is added to a solution of less reactive metal. When a less reactive metal is added to a solution of a more reactive metal, no reaction takes place as a less reactive cannot displace the more reactive metal.

Iron nail dipped in copper sulphate

From the reactivity series, iron (Fe) is a more reactive metal than copper (Cu). Therefore, when the iron is added to copper sulphate $\left({\mathrm{CuSO}}_4\right)$ solution, it displaces copper and forms ferrous sulphate $\left({\mathrm{FeSO}}_4\right)$. Copper is deposited in its elemental form.

The equation for the displacement reaction is:

$$\begin{gathered} \mathrm{Fe}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{FeSO}}_4\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right) \\ \mathrm{blue}\mathrm{light}\mathrm{green}\mathrm{reddish}-\mathrm{brown} \end{gathered}$$

During the displacement reaction, the blue coloured copper sulphate solution is converted into light green coloured ferrous sulphate. Also, the reddish-brown copper is formed which gets deposited on the surface of the iron nail.

Therefore, the two observations will be:

• The solution will turn light green from blue.
• The iron nail will develop a reddish-brown layer of copper.