Biomolecules and Chemistry in Everyday Life 1 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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Solution:
- Both fructose and glucose give following test positive.
(i) Fehling’s test (red ppt. of $\mathrm{Cu}_{2} \mathrm{O}$ is obtained).
(ii) Barfoed’s test (red ppt. of $\mathrm{Cu}_{2} \mathrm{O}$ is obtained)
(iii) Benedict’s test (red ppt. of $\mathrm{Cu}{2} \mathrm{O}$ is obtained) Fehling’s solution: $\mathrm{CuSO}{4}+\mathrm{Na}, \mathrm{K}$-tartrate (Rochelle salt) Barfoed’s reagent $\left(\mathrm{CH}{3} \mathrm{COO}\right){2} \mathrm{Cu}+\mathrm{CH}{3} \mathrm{COOH}+\mathrm{H}{2} \mathrm{O}$
Benedict’s solution: $\mathrm{CuSO}{4}+\mathrm{Na}$-citrate $+\mathrm{Na}{2} \mathrm{CO}_{3}$
Seliwanoff’s test is used to differentiate between ketose and aldose. The reagent is a solution of resorcinol in concentrated $\mathrm{HCl}$. 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).
