When aldehyde is warmed with Fehling reagent;
Correct answer: A. A red precipitate of CuO is formed
- A. A red precipitate of CuO is formed
- B. A black precipitate of CuO is formed
- C. Silver mirror is formed
- D. No reaction occurs
Explanation
Aldehyde reacts with Fehling reagent through the following reaction: Diagram This is an oxidation reaction in which copper oxidizes alkyl halide and itself reduces from (Cu2+) +2 to (Cu2O) +1 giving a red-brown precipitate hence it is the correct answer.
This question appeared on the ETEA MDCAT 2005 paper, which you can sit online with every answer explained.
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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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