Two organic compounds K and L were treated with a few drops of Fehling's solutions respectively . K formed a…

1. Analyze the Question

The question tests your knowledge of functional group identification in organic chemistry using chemical tests. Specifically, it asks you to identify a compound that reacts with Fehling's solution to produce a brick-red precipitate.

2. Explain the Concept

Fehling's solution is a chemical reagent used to distinguish between aldehydes (alkanals) and ketones (alkanones).

• Fehling's Test: When Fehling's solution (a mixture of Fehling's A and B) is heated with an alkanal (aldehyde), the aldehyde is oxidized to a carboxylic acid, and the copper(II) ions in the solution are reduced to copper(I) oxide, which forms a brick-red precipitate.
• Ketones (Alkanones): Ketones are generally resistant to oxidation and do not react with Fehling's solution. Therefore, the solution remains unchanged (blue).
• Alkanols and Alkanes: These do not react with Fehling's solution under standard conditions.

3. Show the Solution

• Step 1: Identify the purpose of the test. The formation of a brick-red precipitate is a positive test for the presence of an aldehyde group (-CHO).
• Step 2: Match the result to the functional group. Since compound K produced the brick-red precipitate, K must be an alkanal.
• Step 3: Evaluate the options. • Alkanol: Does not react with Fehling's solution. • Alkane: Does not react with Fehling's solution. • Alkanal: Reacts with Fehling's solution to give a brick-red precipitate. • Alkanone: Does not react with Fehling's solution.

4. Identify the Answer

Based on the chemical properties of aldehydes, compound K is an alkanal.

Correct Option: C

5. Exam Tip

Remember the "Tollens' and Fehling's Rule": Both Tollens' reagent (silver mirror test) and Fehling's solution are specific to alkanals. If you see "brick-red precipitate" or "silver mirror," immediately think of an alkanal (aldehyde). Ketones are "too stubborn" to react with these mild oxidizing agents!