Question

What do you observe when:
(i) Iodine crystals are heated in the test tube?
(ii) Iron nails are added to copper sulphate solution?

Answer 1

Hint: (i) Iodine exists as ${I_2}$ in standard condition. Van der Waals force of attraction between molecules of ${I_2}$.
(ii) In accordance with the reactivity series copper is less reactive than iron. The more reactive metals can displace the less reactive metals from the compound.

Complete step by step solution:
(i) ${I_2}$ is a nonpolar molecule. These types of molecules don't have permanent dipole moments, that is the electrons in non-polar molecules form a temporary dipole which creates dispersion forces and the intermolecular attraction between the molecules are Van der Waals dispersion forces. In the case of ${I_2}$ molecules, the dispersion force is strong enough to hold iodine molecules together so it exists as solid. On heating, the van der Waals dispersion forces existing then will easily break as it has a low boiling point and sublimates into gas.
On heating iodine in the test tube, iodine evolves as violet fuming gas.
(ii)If we refer to the reactivity series, we can spot that Iron is more reactive than copper. Displacement reaction can be defined as a type of chemical reaction where one element is displaced by another element in the compound.
When iron nails are added to copper sulphate solution this undergoes displacement reaction. As iron is more reactive than copper it has a greater tendency to lose the electrons and form positive ions by displacing cupric ions in copper sulphate.
Metallic iron is converted to ferrous iron ($F{e^{ + 2}}$) and cupric iron ($C{u^{ + 2}}$) is converted to metallic copper.
\[Fe + CuS{O_4} \to FeS{O_4} + Cu\]
For better understanding this reaction can be written as:
\[Fe + C{u^{ + 2}} \to F{e^{ + 2}} + Cu\]
Practically if we perform this the blue colour solution of copper sulphate will turn greenish-blue when iron nails are added to it.

Note: (i) ${I_2}$ has a low boiling point as the Van der Waals dispersion force is easily broken on heating.
(ii)The reaction is a displacement reaction. The blue colour of copper sulphate will turn greenish-blue on adding iron nails to copper sulphate solution.