Consider the following statements about Fehling’s test.
(A) Fehling solution A is aqueous copper sulphate.
(B) Fehling solution B is alkaline sodium potassium tartrate (Rochelle salt).
(C) On heating an aldehyde with Fehling’s reagent, a white precipitate is obtained.
(D) In Fehling’s test, the aldehyde is reduced to the corresponding alcohol.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C) and (D) only
Fehling’s reagent is a mild oxidising agent made by mixing Fehling solutions A and B in equal amounts just before the test. It oxidises an aldehyde, and its copper(II) is reduced to a reddish brown precipitate.
(A) Fehling solution A is aqueous copper sulphate. — Correct statement. Solution A supplies the copper(II) ions.
(B) Fehling solution B is alkaline sodium potassium tartrate (Rochelle salt). — Correct statement. Solution B makes the mixture alkaline and holds the copper(II) ions in solution as a tartrate complex.
(C) On heating an aldehyde with Fehling’s reagent, a white precipitate is obtained. — Incorrect statement. The precipitate is reddish brown.
(D) In Fehling’s test, the aldehyde is reduced to the corresponding alcohol. — Incorrect statement. The aldehyde is the substance oxidised; it is converted into the corresponding carboxylate anion, while the reagent is reduced.
NCERT (2026-27 edition):
8.4 Chemical Reactions – “(ii) Fehling’s test: Fehling reagent comprises of two solutions, Fehling solution A and Fehling solution B. Fehling solution A is aqueous copper sulphate and Fehling solution B is alkaline sodium potassium tartarate (Rochelle salt). These two solutions are mixed in equal amounts before test. On heating an aldehyde with Fehling’s reagent, a reddish brown precipitate is obtained. Aldehydes are oxidised to corresponding carboxylate anion.”