Question

Which one of the following can be purified by sublimation?
(a) ${F_2}$
(b) $C{l_2}$
(c) $B{r_2}$
(d) ${I_2}$

Answer 1

Here, we have to know about what are the different types of purification, which elements are purified by which method, what is sublimation, which element can be purified by these and how the elements are purified in these methods.

Complete answer:
Let’s start with why purification is needed.The elements are not present in their pure state in nature, they are present in the form of compounds when they are extracted from the ore. So, to obtain the pure form of the elements we have to purify them.
Now, what is sublimation?
Sublimation: When any solid is directly converted into gas without converting into the liquid phase is called sublimation. Sublimation is mostly used for separation of non-volatile compounds from volatile compounds. In sublimation, the volatile compounds evaporate leaving non-volatile compounds as residue.
The substance shows sublimation: The elements having volatile nature undergo sublimation (Volatile means the compounds which easily evaporate).
So, in the given options, only iodine has volatile nature, because it can directly change into the gas without changing into liquid.
Hence, the correct option is (d) ${I_2}$ .

Additional Information: Different methods of the Purification of metals:
(a) Distillation: The metals having low boiling point are purified by these methods. For example: Mercury, Zinc etc.
(b) Liquation: The metals having low melting point are purified by these methods. For example: Tin, Lead etc.
(c) Electrolysis: In this method, electricity is used and copper is purified by this method.
(d) Zone Refining: Metals like semiconductors are purified by this process. For example: Germanium, silicon etc.
(e) Vapour Phase Refining: The metals having volatile and easily decomposable metals are purified by these methods. Nickel is purified by this method.

Note: For sublimation, it is necessary to know which elements are volatile in nature and which are not. Dry ice ( that is solid $C{O_2}$ ), Naphthalene balls are the common examples of the volatile compounds. Sublimation is mostly used for separation of non-volatile compounds from volatile compounds.