On heating aldehydes with Fehlings solution we get a precipitate whose colour is_________________?
Correct answer: D. brick red
- A. pink
- B. black
- C. yellow
- D. brick red
Explanation
Aldehydes reduce the blue Cu2+ ions in Fehling's solution to insoluble Cu2O, which forms a brick-red precipitate, while the aldehyde is oxidized to a carboxylate. Ketones generally do not give this test. Students may choose yellow because some copper compounds appear yellow or because they confuse this test with another precipitate test, but Fehling's positive result is brick red.
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About Reactivity of Aldehydes and Ketones
The polar carbonyl group makes aldehydes and ketones undergo nucleophilic addition, reduction and condensation reactions. Aldehydes are generally more reactive and oxidise readily to carboxylic acids, whereas ketones resist mild oxidation; reactions with hydrogen cyanide, sodium bisulfite and 2,4-DNP help identify their behaviour.
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679 free Aldehydes and Ketones MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
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