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Biomolecules
Carbohydrates: Reducing Sugars
1 question from 1 paper, each with its answer.
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Concepts tested
- Fehling's test for reducing sugars
All Questions
2001 AIPMT 1 question
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Which of the following gives positive Fehling solution testFehling's solution (alkaline $Cu^{2+}$ complex) is reduced by compounds having a free aldehyde group, giving a red precipitate of $Cu_2O$.
Glucose is an aldose with a free (potential) aldehyde group, so it is a reducing sugar and gives a positive test.
In sucrose, the carbonyl groups of glucose and fructose are linked to each other in the glycosidic bond, so it is non-reducing. Fats and proteins do not have free aldehyde groups.
So glucose gives a positive Fehling's test.