Question

How will you distinguish between Ethanol and Methanol using the Iodoform test?

Hint:

{Iodoform test:} Ethanol → Yellow precipitate (positive) Methanol → No precipitate (negative)

Answer 1

Concept: The iodoform test is used to identify compounds containing the methyl ketone group (\(-COCH_3\)) or alcohols that can be oxidized to it. Ethanol is the only primary alcohol that gives a positive iodoform test because it can be oxidized to acetaldehyde. Procedure: Add iodine solution and sodium hydroxide (NaOH) to the given alcohol and warm gently. Observation:

• Ethanol: Produces a yellow precipitate of iodoform (\(CHI_3\)) with a characteristic antiseptic smell.
• Methanol: Does not produce any yellow precipitate (negative test).

Reason:

• Ethanol is oxidized to acetaldehyde (\(CH_3CHO\)), which contains the required methyl carbonyl group and gives the iodoform reaction.
• Methanol is oxidized to formaldehyde (\(HCHO\)), which does not contain the methyl group required for the test.

Conclusion: Thus, ethanol can be distinguished from methanol because ethanol gives a positive iodoform test (yellow precipitate), while methanol does not.