An aldehyde when strongly heated with Fehling's reagent gives red precipitate. What property of an aldehyde is observed in this reaction?
Correct answer: D. Redox property.
- A. Reducing property.
- B. Oxidizing property.
- C. Neutralizing ability.
- D. Redox property.
Explanation
Aliphatic aldehydes form a brick-red precipitate with Fehling's solution. To an aldehyde solution, add Fehling's solution and boil. A brick red precipitate of cuprous oxide is formed. Ketones do not give this test. The aldehyde group of sugar is oxidised by complexed copper ions to form acid. The red copper (I) oxide then precipitates, which is an indicator for the redox reaction.
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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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