Question

Fructose and glucose can be distinguished by:
(a) Fehling’s test
(b) Barfoed’s test
(c) Benedict’s test
(d) Seliwanoff’s test

Answer 1

Hint: Both the glucose and the fructose are the monosaccharides but glucose is an aldose and fructose is a ketose. So, identify that test from the above given tests which is used to distinguish between the aldose and ketose and you will get your answer.

Complete step by step answer:
First of all, let’s discuss glucose and fructose. Both the glucose and the fructose are the carbohydrates. Carbohydrates are the polyhydroxy aldehydes or polyhydroxy ketones or the substances which give these on hydrolysis and contain at least one chiral carbon atom.
Glucose is an aldose monosaccharide i.e. it consists of the aldehyde group i.e. $-CHO$ group.
Glucose is crystalline white solid with the melting point of $419K$. It is highly soluble in water but sparingly soluble in alcohol and insoluble in ether
On the other hand, fructose is a ketose monosaccharide i.e. it consists of the keto group i.e.$-C=O$ group.
Fructose is colorless, crystalline solid with the melting point of $375K$. It is the sweetest of all sugars and highly soluble in water and alcohol than the glucose.
Now considering the statement;
We will discuss, the given options one by one;
(a) Fehling’s test: It is the test used to distinguish between the aldehydes and ketones.
(b) Barfoed’s test: It is used to detect the presence of the monosaccharides.
(c) Benedict’s test: It is used to distinguish between the aliphatic and the aromatic aldehydes.
(d) Seliwanoff’s Test: It is used to distinguish between the aldose and ketose.
So, from this it is clear that we can distinguish between the fructose and glucose by Seliwanoff’s test because fructose is a ketose and glucose is an aldose.

Hence option (d) is correct.

Note: All those carbohydrates which contain the aldehydic or the ketonic group reduces the Tollen’s reagent or the Fehling’s solution and are called as the reducing carbohydrates or sugars whereas the others which do not reduce these reagents are called as the non-reducing carbohydrates.