Question

Methanol and ethanol are distinguished by-
A.Treating with Schiff’s reagent
B.Treating with Lucas reagent
C.Heating with iodine and alkali
D.Treating with $Cr{O_3}$ in $dil.{H_2}S{O_4}$

Answer 1

Hint:We need to know the process of identification and distinguishing different types of alcohol. Methanol and ethanol are very important organic solvents in organic synthesis reactions. It is used variedly as antifreeze, solvent, fuel, and as a denaturant for ethanol. It is also used to produce biodiesel via transesterification reaction. Ethanol is used externally as antiseptic for wounds at concentration 70%, in wine preparation, perfumes, etc. Because of their completely different uses, it is necessary to distinguish between the two.

Complete step by step answer:
Alcohol can be distinguished based on both physical and chemical properties. Physical properties include the state, colour, odour, Miscibility, etc. The chemical properties include treatment of the alcohols with various chemical reagents and based on the response to those reagents, we can distinguish between alcohols.
Let us study each of the given reagents:
A.Treating with Schiff’s reagent: The Schiff test is a chemical test used to check for the presence of aldehydes. It can be used to differentiate between aldehyde and ketones and not to distinguish between alcohols.
B.Treating with Lucas reagent: The Lucas test in alcohols is a test to differentiate between primary, secondary, and tertiary alcohols. Methanol and ethanol are both primary alcohols hence this test is not applicable to distinguish between the two.
C.Heating with iodine and alkali: This is known as the iodoform test. When ethanol is heated with iodine in the presence of an alkali NaOH, it forms a yellow -coloured precipitate. On the other hand, methanol does not react to this test. Hence this method is used to distinguish between ethanol and methanol.
D.Treating with $Cr{O_3}$ in $dil.{H_2}S{O_4}$: This combination is known as the Jones reagent which is used in the conversion of secondary alcohols to ketones and of most primary alcohols to carboxylic acids. Hence it cannot be used to distinguish between ethanol and methanol.
Therefore, methanol and ethanol are distinguished by heating with iodine and alkali.
Hence the correct option is option (C).

Note:
It must be noted that the iodoform test does not confirm the presence of methanol. When there is no yellow-coloured precipitate when allowed to react with iodine and\[NaOH\], it may be due to the presence of methanol or glycerol. But if the solution has a fruity odour, it confirms the presence of methanol.