Biomolecules and Chemistry in Everyday Life - Result Question 46

####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:

  1. 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).



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