MCQ Detailed View

Schiff’s reagent is a well-known test in organic chemistry to identify aldehydes. It is made by treating fuchsine dye with sulfur dioxide, which removes its color. The resulting solution is almost colorless. When this reagent comes in contact with an aldehyde, the aldehyde restores the color of the dye, and the solution turns pink or magenta. This simple color change makes Schiff’s test a very useful way to detect aldehyde groups.

Among the given options, acetaldehyde (CH₃–CHO) is an aldehyde. It has the characteristic –CHO group where the carbon atom of the carbonyl group is directly attached to a hydrogen atom. This structure makes aldehydes highly reactive in Schiff’s test. When acetaldehyde is tested with Schiff’s reagent, the pink color appears, showing a positive result.

The other options do not give this reaction. Acetone is a ketone (CH₃–CO–CH₃). Ketones do not normally react with Schiff’s reagent because they are less reactive than aldehydes in this type of test. Acetic acid (CH₃–COOH) is a carboxylic acid, and its carbonyl group is stabilized by resonance and cannot reduce the reagent, so it does not produce the pink color. Methyl acetate (CH₃–COOCH₃) is an ester, and esters also fail Schiff’s test for the same reason.

This means only aldehydes, like acetaldehyde, show a clear positive Schiff’s test by restoring the pink color. This test is part of classical qualitative organic analysis and is important in laboratories for distinguishing aldehydes from ketones, acids, and esters. It provides students with a simple way to connect functional groups with practical chemical tests.