Question

What is the molecular formula of the most common disaccharide?

Answer 1

Hint: Saccharides are carbohydrates. Monosaccharide is the simplest carbohydrate which cannot hydrolyze further to give a smaller compound. Disaccharide are those which upon hydrolysis give two molecules of monosaccharides.

Complete answer:
Carbohydrates are the hydrates of carbon. Monosaccharides are simplest carbohydrates which cannot hydrolyze further to give a smaller compound. Disaccharides are those which upon hydrolysis give two molecules of monosaccharides. The most common disaccharide Is sucrose which is mainly derived from plants. The molecular formula for sucrose is \[{{C}_{12}}{{H}_{22}}{{O}_{11}}\]. Sucrose on acid hydrolysis gives an equimolar mixture of two monosaccharides which is glucose and fructose. This is illustrated in the following diagram:

During this hydrolysis, the optical rotation of the solution changes from dextrorotatory to levorotatory. Thus, the above process is called inversion of sugar and the resulting solution is called invert sugar.

Additional information: In biological processes, the hydrolysis of sugar takes place in the presence of sucrase enzymes. Both monosaccharide units are joined to each other through their reducing centre i.e. carbonyl groups that’s why sucrose is non-reducing sugar. Non-reducing sugars are those which don't give Tollen’s reagent and Fehling solution test. As, sucrose is synthesized from the sugarcane and thus it is also called cane-sugar.

Note:
It is important to note that the most common disaccharide is sucrose which is also called table sugar. The molecular formula for sucrose is \[{{C}_{12}}{{H}_{22}}{{O}_{11}}\] . It is an example of non- reducing sugar i.e. doesn’t give the Fehling and Tollens test.