On heating aldehydes with Fehling's solution, we get a precipitate whose colour is
Correct answer: D. brick red
- A. pink
- B. black
- C. yellow
- D. brick red
Explanation
Fehling's solution is a powerful tool for identifying aldehydes (and some α-hydroxy ketones). When you heat an aldehyde with Fehling's solution following reaction occurs:Oxidation: The aldehyde gets oxidized by the copper ions (Cu²⁺) present in the solution, losing its carbonyl group and gaining two hydroxyl groups.Reduction: The copper ions themselves get reduced from Cu²⁺ to Cu⁺ ions in the process.Precipitation: The Cu⁺ ions form a characteristic brick-red precipitate of cuprous oxide (Cu₂O), revealing the presence of an aldehyde.
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About Aldehydes and Ketones
Aldehydes and ketones contain the polar carbonyl group, but aldehydes are generally more readily oxidised and more reactive than ketones. Coverage includes preparation by oxidation or reduction routes, nucleophilic addition of reagents such as hydrogen cyanide and bisulfite, and tests that distinguish aldehydes from ketones.
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