Organic Chemistry Of Natural polymers (Carbohydrates, proteins, and natural rubber vulcanization)

 

Natural Polymers: Carbohydrates, Proteins, and Rubber

In chemistry, polymers are large molecules (macromolecules) formed by the repeated linking of smaller units called monomers. Natural polymers are those derived from plants and animals.

Key Definitions

  • Carbohydrates: Organic compounds made of carbon, hydrogen, and oxygen, usually with a hydrogen-to-oxygen ratio of 2:1 (like water). They include sugars, starches, and cellulose.
  • Proteins: Complex, high-molecular-weight natural polymers composed of amino acid monomers linked together by peptide bonds. They are essential for the structure and function of living cells.
  • Natural Rubber: A polymer of 2-methylbuta-1,3-diene (isoprene). In its raw state, it is sticky when hot and brittle when cold.
  • Vulcanization: A chemical process of heating raw rubber with sulfur (and other additives) to create cross-links between polymer chains. This improves its elasticity, tensile strength, and resistance to temperature changes.
  • Condensation Polymerization: A process where monomers join together with the elimination of a small molecule, such as water or ammonia (e.g., formation of starch and proteins).
  • Addition Polymerization: A process where monomers containing double or triple bonds join together without the loss of any atoms or molecules (e.g., formation of natural rubber).

WAEC Practice Questions (Objectives)

1. Which of the following pairs of natural polymers are formed by condensation polymerization?

A. Rubber and Starch
B. Cellulose and Protein
C. Polyethene and Glycogen
D. Nylon and Isoprene

2. The monomer of natural rubber is:

A. Buta-1,3-diene
B. 2-methylbuta-1,3-diene
C. Ethyne
D. Propene

3. What is the primary purpose of vulcanizing natural rubber?

A. To make it more soluble in organic solvents
B. To change its color
C. To increase its tensile strength and elasticity
D. To convert it into a carbohydrate

4. Proteins are polymers of amino acids held together by:

A. Glycosidic linkages
B. Ester bonds
C. Peptide bonds
D. Hydrogen bonds

5. Which of the following carbohydrates is a polysaccharide?

A. Glucose
B. Sucrose
C. Fructose
D. Cellulose

6. During the vulcanization of rubber, the chemical element added is:

A. Nitrogen
B. Chlorine
C. Sulfur
D. Carbon

7. Complete hydrolysis of starch yields:

A. Glucose only
B. Glucose and Fructose
C. Amino acids
D. Maltose only

8. Which of the following chemical tests can be used to identify proteins?

A. Benedict's test
B. Biuret test
C. Iodine test
D. Fehling's test

9. Carbohydrates are represented generally by the empirical formula:

A. Cx(H2O)y
B. CnH2n+2
C. R-COOH
D. CnH2nO

10. When iodine solution is added to a sample of boiled cassava paste, the color changes to:

A. Brick red
B. Deep blue-black
C. Purple
D. Clear colorless

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