Question

A mixture of o - nitrophenol and p - nitrophenol can be separated by steam distillation.
Reason: p - nitrophenol is a steam volatile whereas o - nitrophenol l is not a steam volatile.
(A) Both reason and assertion are correct. Reason is the correct explanation for assertion
(B) Both reason and assertion are correct but Reason is not the correct explanation for assertion
(C) Assertion is correct but reason is incorrect
(D) Both reason and assertion are incorrect

Answer 1

Hint: Steam distillation is distillation of a liquid in the form of steam, used for the purification of non-volatile and immiscible liquids. The liquid that evaporates easily at room temperature are known as volatile liquid for example: rubbing alcohol (isopropyl alcohol) and the liquids that do not evaporate easily at room temperature are said to be non-volatile for example vegetable oil. The position of the nitro group is one of the factor of the liquid being volatile as it gets easier to form hydrogen bond

Complete answer:
Steam distillation is a technique used for separating substances which are immiscible with water, having high vapour pressure at the boiling temperature of water and volatile in steam.
At o-nitrophenol Intramolecular hydrogen bonding is present. This is because the polar nature of the formed O - H bonds results in the formation of hydrogen bonds within the same molecule. This intermolecular hydrogen bonding results in reduced water solubility and volatility was increased. Whereas p-intermolecular bonding that took place between O & H atoms of two different p-nitro phenol molecules is possible. There is an increase of molecular weight of p - nitrophenol as it undergoes association because of inter molecular hydrogen bonding and thereby decreasing volatility. Hence p - nitrophenol l is not steam distillable .i.e. non-volatile and o - nitrophenol is steam distillable .i.e. volatile.
Hence the answer is C ; The mixture of o - nitrophenol and p - nitrophenol can be separated by steam distillation but o - nitrophenol is steam volatile.

Note:
Hydrogen bonding or H-bonding is a dipole-dipole attraction between molecules or atoms. There are two types of hydrogen bonding .i.e. inter and intramolecular hydrogen bonding. Intermolecular means bond occurring between the same molecules whereas intra molecular means occurring among the parts of the same molecule.