Question

What is Bial’s test?

Answer 1

Hint: As we know that Bial’s test is a chemical test for the presence of pentoses in the compound or substance given. It is named after a German physician, Manfred Bial. The components of the test include orcinol, hydrochloric acid (HCl) and ferric chloride ($FeC{{l}_{3}}$). If pentose is present then it will get dehydrated to form furfural which then reacts with the orcinol to generate a colored substance. So here we have to talk about Bial’s test.

Complete answer:
Let us discuss about Bial’s test as follows:-
-Bial’s test: It is a chemical test for the presence of pentoses in the compound or substance given. It is named after a German physician, Manfred Bial. The components of the test include orcinol, hydrochloric acid (HCl) and ferric chloride ($FeC{{l}_{3}}$). If pentose is present then it will get dehydrated to form furfural which then reacts with the orcinol to produce a colored substance.
-The procedure of Bial’s test is as follows:-
The Bial’s reagent consists of 0.4 grams of orcinol, 200 ml of concentrated HCl and 0.5 ml of a 10% solution of $FeC{{l}_{3}}$. The saccharides get dehydrated to form furfural derivatives that develop colour with Bial’s reagent.
-The indication of the presence of pentoses in the saccharides is as follows:-
 A blue-green colour formation indicates nucleotides containing pentoses whereas a yellow-green colour indicates hexoses and disaccharides obtain yellow colour.
-Inference:-
This test distinguishes between monosaccharides and disaccharides. It should be noted that Bial’s test is generally used to distinguish between pentoses and hexoses and hence often conducted after these groups have been identified with the help of Molisch’s test.

Note:
-Remember that lactose does not react with Bial’s reagent and hence we cannot identify anything in its presence.
-Also Molisch’s test is a test which tells about the presence of pentoses and hexoses in the substance provided for the test.