Chapter 23, Problem 67A

Interpretation Introduction

Interpretation: To predict the products of the given aldehydes when they are made to react with Fehling’s reagent.

Concept Introduction: Fehling’s test is mainly used to distinguish between the aldehyde and the ketone. If a carbonyl compound gives a positive Fehling test, then it is confirmed as an aliphatic aldehyde. Fehling’s regent cannot oxidize the aromatic aldehyde.

Answer to Problem 67A

  

  

  

Explanation of Solution

Fehling’s solution is of two types

Fehling’s A and Fehling’s B. Fehling’s A is the Copper (II) hydroxide where as Fehling’s B is the Rochelle salt. When the aldehydes are made to react with the Cuprous ion and the hydroxide ion, the carboxylate ion along with the Cuprous (II) oxide which is a red precipitate is formed. This process takes place with the removal of water molecules.

Conclusion

Fehling’s test is used only to distinguish aliphatic aldehydes from ketones. In the given examples the first one is benzaldehyde which is an aromatic aldehyde therefore, it gives the negative test with Fehling’s solution. Whereas, the other two are aliphatic aldehydes that give the positive test with Fehling’s solution.