In Tollen's test, aldehydes (A) Are oxidised to acids (B) Are reduced to alcohol (C) Neither reduced nor oxidised (D) Precipitate Ag+ as AgCI

Tollen's test is a classic qualitative test used to identify aldehydes. The correct answer to your question is (A) Are oxidised to acids. Let’s delve into the details of this reaction and why aldehydes behave this way in Tollen's test.

Understanding Tollen's Reagent

Tollen's reagent is a solution of silver nitrate (AgNO3) in ammonia (NH3). It is a mild oxidizing agent specifically designed to react with aldehydes. When an aldehyde is present, it undergoes oxidation, while the silver ions (Ag+) in Tollen's reagent are reduced to metallic silver (Ag).

The Reaction Process

Here's how the reaction unfolds:

• The aldehyde group (-CHO) in the aldehyde molecule is oxidized to a carboxylic acid (-COOH).
• Simultaneously, the silver ions in Tollen's reagent are reduced to form a shiny metallic silver precipitate.

Why Aldehydes Are Oxidized

Aldehydes are more reactive than ketones and can easily undergo oxidation due to the presence of the hydrogen atom attached to the carbonyl group. This makes them susceptible to oxidation, which is a key characteristic that distinguishes them from other carbonyl compounds.

Visualizing the Reaction

To visualize this, consider the following analogy: think of the aldehyde as a piece of wood that can be easily burned (oxidized) to produce ash (the carboxylic acid). The silver ions in Tollen's reagent act like a flame that not only burns the wood but also leaves behind a shiny silver coating (the precipitate).

What Happens in Tollen's Test

When you perform Tollen's test with an aldehyde, you will observe the formation of a silver mirror on the inner walls of the test tube. This is due to the reduction of silver ions to metallic silver, which is a hallmark of a positive test for aldehydes.

Other Options Explained

• Option B (Are reduced to alcohol): This is incorrect because aldehydes do not get reduced in Tollen's test; they are oxidized.
• Option C (Neither reduced nor oxidised): This is also incorrect, as the aldehyde is definitely undergoing oxidation.
• Option D (Precipitate Ag+ as AgCl): This is misleading; while silver chloride (AgCl) can precipitate in other reactions, Tollen's test specifically involves the reduction of Ag+ to Ag, not AgCl.

Summary of Tollen's Test

In summary, Tollen's test is a reliable method for identifying aldehydes through their oxidation to carboxylic acids and the concurrent reduction of silver ions to metallic silver. This reaction not only helps in distinguishing aldehydes from other carbonyl compounds but also provides a visual cue through the formation of a silver mirror. Understanding this reaction is crucial for students studying organic chemistry and its applications in identifying functional groups.