What is the colour of copper compound formed in Fehling’s test for aliphatic aldehydes ?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Red brown
On heating with Fehling’s reagent, an aliphatic aldehyde reduces the blue \( \ce{Cu^2+} \) complex to copper(I) oxide, which separates as a red-brown precipitate:
\( \displaystyle \ce{R-CHO + 2Cu^2+ + 5OH^- -> RCOO^- + Cu2O v + 3H2O} \)
So the copper compound formed is \( \ce{Cu2O} \), red brown in colour. Aromatic aldehydes do not respond to this test.
NCERT (2026-27 edition):
Fehling’s Test
