Target Exam

CUET

Subject

Chemistry

Chapter

Organic: Aldehydes, Ketones and Carboxylic Acids

Question:

Read the passage carefully and answer the following questions.

Aldehydes, carboxylic acids and ketones are widespread in the animal and plant kingdoms. They play a pivotal role in various biochemical processes of life. Their presence in nature adds fragrance and flavor. These compounds are widely used in food products, pharmaceuticals, paints, resins and other important product industries. These compounds are prepared by various laboratory methods, which mainly include oxidation, formylation, acylation and reduction. Due to the polar nature of the carbonyl group in aldehydes and ketones, they can exhibit different reactions like nucleophilic addition. They do exhibit redox and various condensation reactions which lead to the formation of various important compounds. On the other hand, the carboxylic acids are mainly prepared by oxidation and hydrolysis of different compounds. The carboxylic acid consists of a carbonyl group and the hydroxy group (attached to the carbonyl carbon atom). This makes it possible for the carboxylic acid to participate in various chemical reactions which involve cleavage of the C-OH bond and the O-H bond along with the reactions involving the complete -COOH group.

The reagent which doesn't react with both acetone and benzaldehyde is:

Options:

Sodium hydrogensulphite

Phenyl hydrazine

Fehling's solution

Grignard reagent

Correct Answer:

Fehling's solution

Explanation:

The correct answer is Option (3) → Fehling's solution
Fehling’s solution does not react with both acetone and benzaldehyde.

Reasoning:
• Acetone is a ketone. Fehling’s solution does not react with ketones.
• Benzaldehyde is an aromatic aldehyde. Fehling’s solution reacts only with aliphatic aldehydes, not aromatic aldehydes like benzaldehyde.
• Hence, both acetone and benzaldehyde give a negative test with Fehling’s solution.

Why others are incorrect:
Sodium hydrogensulphite reacts with both aldehydes and ketones by forming addition compounds.
Phenyl hydrazine reacts with both to form hydrazones.
Grignard reagent reacts with both aldehydes and ketones to form alcohols.

Therefore, the only reagent that doesn’t react with both is Fehling’s solution.