Fehling's solution is reduced to a red precipitate of copper one oxide by
Correct answer: D. ethanal
- A. propanone
- B. benzaldehyde
- C. ethanol
- D. ethanal
Explanation
Aliphatic aldehydes such as ethanal reduce the blue copper two complex to a brick red precipitate, whereas ketones do not react at all. Aromatic aldehydes such as benzaldehyde are the notable exception, since they give a negative result with Fehling's solution although they do respond to Tollens reagent. Ethanol must first be oxidised to an aldehyde before it could react.
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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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