Question

Methanol and ethanol are distinguished by

• A. Treating with Schiff's reagent
• B. Treating Lucas agent
• C. Heating with Iodine and alkali
• D. Treating with ${\mathrm{CrO}}_3$ in dil.${\mathrm{H}}_2{\mathrm{SO}}_4$

Answer 1

The correct option is C

Heating with Iodine and alkali

Explanation of correct answer:

Option C Heating with Iodine and alkali

• Methanol$\left({\mathrm{CH}}_3\mathrm{OH}\right)$ consists of one Carbon and Ethanol$\left({\mathrm{C}}_2{\mathrm{H}}_6\mathrm{O}\right)$ consist of two Carbon atom.
• Methanol and Ethanol cannot be distinguished physically as they appear the same that is why we use chemical tests to distinguish them, so they can be distinguished by chemical methods only,
• Methanol and ethanol are distinguished by a chemical test known as Iodoform
• The Ethanol is warmed with Iodine in the presence of NaOH, which forms a yellow-colored precipitate and it is the only primary alcohol that gives the iodoform test. $\underset{\mathrm{Ethanol}}{{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}}+\underset{\mathrm{Iodine}}{{\mathrm{I}}_2}+\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\mathrm{NaOH}}\to \underset{\mathrm{Triiodomethane}}{{\mathrm{CHI}}_3}+\underset{\mathrm{Formate}\mathrm{ion}}{{\mathrm{HCOO}}^{-}}+\underset{\mathrm{Sodium}\mathrm{ion}}{{\mathrm{Na}}^{+}}$
• However, Methanol does not react positively to the Iodoform test.
• Hence, option C Heating with Iodine and alkali is correct.

Explanation of correct answer:

Option A Treating with Schiff's reagent

• The Schiff test is a chemical test used to check for the presence of aldehydes.
• So Schiff test can't be used for distinguishing Methanol and Ethanol
• Hence option A Treating with Schiff's reagent is incorrect.

Option B Treating Lucas's agent

• Both of them react with Lucas's reagent very slowly only on boiling.
• So Lucas's reagent can't be used for distinguishing Methanol and Ethanol
• Hence option B Treating Lucas's agent is incorrect.

Option C Treating with ${\mathrm{CrO}}_3$ in dil.${\mathrm{H}}_2{\mathrm{SO}}_4$

• Jones reagent is a solution prepared by dissolving Chromium trioxide in aqueous Sulfuric acid.
• The Jones reagent oxidizes primary alcohols to carboxylic acids.
• So Lucas's reagent can't be used for distinguishing Methanol and Ethanol.
• Hence option C treating with ${\mathrm{CrO}}_3$ in dil.${\mathrm{H}}_2{\mathrm{SO}}_4$ is incorrect.