Fehling solution react with HCHO to form precipitate of _____________?
Correct answer: C. Red colour
- A. White colour
- B. Yellow colour
- C. Red colour
- D. Blue colour
Explanation
HCHO reduces Fehling solution, converting blue Cu2+ ions into brick-red Cu2O precipitate while the aldehyde is oxidised to formate or formic acid. The red precipitate is therefore copper(I) oxide, not the original blue copper(II) solution. Students may choose blue because Fehling solution is blue before the 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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