Detailed Description of Carbohydrates | Chemistry for JAMB PDF Download

Carbohydrates

1. Classification

Carbohydrates are organic compounds that consist of carbon, hydrogen, and oxygen atoms. They are classified into three main categories based on their chemical structure and the number of sugar units they contain:

• Monosaccharides: Monosaccharides are the simplest form of carbohydrates. They cannot be further hydrolyzed into smaller sugar units. Examples of monosaccharides include glucose, fructose, and galactose.
• Disaccharides: Disaccharides are formed when two monosaccharides are joined together through a glycosidic bond. Examples of disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).
• Polysaccharides: Polysaccharides are complex carbohydrates composed of multiple monosaccharide units. They can be further classified into two types:
  • Homopolysaccharides: Homopolysaccharides are composed of a single type of monosaccharide. Examples include cellulose, starch, and glycogen.
  • Heteropolysaccharides: Heteropolysaccharides are composed of two or more different types of monosaccharides. Examples include hyaluronic acid and chondroitin sulfate.

2. Composition

Carbohydrates are composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The general formula for carbohydrates is (CH₂O)n, where "n" represents the number of carbon atoms in the molecule. The ratio of hydrogen to oxygen atoms is usually 2:1, similar to water (H₂O).

3. Chemical Tests for Simple Sugars and Reaction with Concentrated Tetraoxosulphate (VI) Acid

Chemical tests can be used to detect the presence of simple sugars (monosaccharides and some disaccharides) in a given sample. Some common tests include:

• Benedict's Test: Benedict's reagent, which contains copper (II) ions, is used to test for reducing sugars. A positive result is indicated by the formation of a brick-red precipitate. Examples of reducing sugars include glucose and maltose.
• Fehling's Test: Fehling's solution, similar to Benedict's reagent, is also used to test for reducing sugars. It produces a reddish precipitate upon reaction with reducing sugars.
• Tollens' Test: Tollens' reagent, which contains silver ions, is used to test for reducing sugars. A positive result is indicated by the formation of a silver mirror on the inner surface of the test tube.

When simple sugars react with concentrated tetraoxosulphate (VI) acid (also known as concentrated sulfuric acid), dehydration or charring occurs. This reaction is used as a test for the presence of carbohydrates, as it leads to the formation of carbon and water.

4. Hydrolysis of Complex Sugars

Complex sugars such as cellulose and starch can be hydrolyzed into their constituent monosaccharides through the process of hydrolysis.

• Hydrolysis of Cellulose: Cellulose, a homopolysaccharide found in the cell walls of plants, can be hydrolyzed by treatment with enzymes such as cellulase. It breaks down cellulose into glucose monomers.
• Hydrolysis of Starch: Starch, another homopolysaccharide, can be hydrolyzed into glucose units by enzymatic action or by treating with dilute acid or heat.

Uses of Sugar and Starch in the Production of Alcoholic Beverages, Pharmaceuticals, and Textiles:

• Alcoholic Beverages: Sugar is used as a fermentable substrate in the production of alcoholic beverages. Yeast enzymes break down sugar (such as glucose and fructose) into alcohol (ethanol) and carbon dioxide through the process of fermentation.
• Pharmaceuticals: Starch is commonly used as an excipient or filler in the production of pharmaceutical tablets and capsules. It provides bulk and aids in the binding of active ingredients.
• Textiles: Starch is used in the textile industry for sizing fabrics, which imparts stiffness and smoothness to the fibers. It helps in preventing yarn breakage during weaving or knitting processes.