Question

The reddish brown deposit formed on iron nails kept in a solution of copper sulphate is:
(A) $C{{u}_{2}}O$
(B) $Cu$
(C) $CuO$
(D) $CuS$

Answer 1

A displacement reaction is a reaction in which one of the atoms or a set of atoms is displaced by another atom in a molecule. Reaction of iron with copper sulphate is the best example for displacement reaction.

Complete step by step solution:
When a nail made up of iron is dipped in copper sulphate solution, a brown coating of copper is formed on the surface of the iron nail.
The color of copper sulphate solution changes from blue color to light green color.
This reaction shows that iron is more reactive than copper.
Iron displaces copper from copper sulphate solution and iron passes into solution and forms ferrous sulphate solution.
This reaction is a best example of a displacement reaction.
$Fe+CuS{{O}_{4}}\xrightarrow{{}}Cu+FeS{{O}_{4}}$
The iron on the surface of the nail will exchange with some of the copper in the solution. So, the iron nail will get a copper coating.
Slowly the blue color copper sulphate solution will start to change to green color ferrous sulphate solution.

So, the correct option is B. copper is going to form a reddish brown color deposit on iron nails.

Note:
- Don’t be confused with copper sulphate and ferrous sulphate. Both are not the same.
- The molecular formula of copper sulphate is $CuS{{O}_{4}}$.
- The molecular formula of ferrous sulphate is $FeS{{O}_{4}}$.