AFTER ADDING FEHLING/ TOLLEN REAGENT IN ALCOHAL . WHAT COLOUR OCCUR

When you add Fehling's or Tollens' reagent to an alcohol, the expected color change depends on the type of alcohol and the specific conditions of the reaction. Both reagents are used primarily to test for aldehydes, not alcohols. However, understanding their reactions can clarify what happens in these scenarios.

Fehling's Reagent Reaction

Fehling's reagent consists of two solutions: Fehling's A, which contains copper(II) sulfate, and Fehling's B, which contains a complexing agent like tartrate. When mixed, they form a deep blue solution due to the presence of copper(II) ions.

What Happens with Aldehydes?

When an aldehyde is present, it reduces the copper(II) ions to copper(I) oxide, which precipitates out of the solution as a brick-red solid. However, if you add Fehling's reagent to a simple alcohol (like ethanol), there will be no reaction, and the solution will remain blue.

Tollens' Reagent Reaction

Tollens' reagent contains silver nitrate in ammonia, which forms a complex that can oxidize aldehydes. The silver ions are reduced to metallic silver, which can deposit on the walls of the reaction vessel, creating a silver mirror effect.

Alcohols and Tollens' Reagent

Similar to Fehling's reagent, if you add Tollens' reagent to an alcohol, no significant reaction occurs, and you won't see any color change. The solution remains clear or slightly cloudy, depending on the concentration of the reagent.

Summary of Color Changes

• Fehling's Reagent: Blue solution remains unchanged with alcohols; brick-red precipitate forms with aldehydes.
• Tollens' Reagent: No color change with alcohols; silver mirror forms with aldehydes.

In summary, neither Fehling's nor Tollens' reagent will produce a color change when added to alcohols, as they are designed to react with aldehydes. If you're working with alcohols and want to test for aldehyde presence, you would need to ensure that the sample contains an aldehyde for a positive result with these reagents.