Biomolecules and Chemistry in Everyday Life - Result Question 7
####7. Fructose and glucose can be distinguished by
(2019 Main, 08 April II)
(a) Fehling’s test
(b) Barfoed’s test
(c) Benedict’s test
(d) Seliwanoff’s test
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Answer:
Correct Answer: 7. (c)
Solution:
- Both fructose and glucose give following test positive.
(i) Fehling’s test (red ppt. of $Cu _2 O$ is obtained).
(ii) Barfoed’s test (red ppt. of $Cu _2 O$ is obtained)
(iii) Benedict’s test (red ppt. of $Cu _2 O$ is obtained) Fehling’s solution: $CuSO _4+Na, K$-tartrate (Rochelle salt) Barfoed’s reagent $\left(CH _3 COO\right) _2 Cu+CH _3 COOH+H _2 O$
Benedict’s solution: $CuSO _4+Na$-citrate $+Na _2 CO _3$
Seliwanoff’s test is used to differentiate between ketose and aldose. The reagent is a solution of resorcinol in concentrated $HCl$. The reagent when heated along with a sugar will produce furfural or hydroxy-methylfurfural, which further reacts to give red color. Ketose (fructose) reacts more quickly than aldose (glucose).
