Fehling's Test

Fehling’s reagent comprises of two solutions i.e. Fehlings A and Fehlings B, Fehlings A is aqueous copper sulphate and Fehlings B is alkaline sodium potassium tartrate also known as Rochelle salt. These two solutions are mixed in equal amount before the test. On heating the aldehyde with Fehling’s reagent a dirty red or reddish brown precipitate is obtained. Aldehydes are oxidized to corresponding Carboxylate anion.

As Fehling’s reagent is a mild oxidizing agent it does not react with Ketones, Fehling’s reagent can be used to differentiate between Aldehydes and Ketones because only aldehydes will undergo reaction.

Fehling’s Reagent is ineffective on Benzaldehyde i.e Aromatic Aldehydes do not respond to this test.