Problem 88 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements is correct about polymers? (1) polymers are substances made up of recurring structural units, each of which can be regarded as derived from a specific compound called a monomer (2) polymers made from a single monomeric species are called homopolymers, whereas, those made up of two or more different monomeric species are called copolymers. (3) very often, polymers are macromolecules, and a sample of a given polymer is characteristically a mixture of molecules with different molecular weights (a) 1 and 2 only (b) 1 and 3 only (c) 1,2 and 3 (d) 2 only

Step-by-Step Solution

Answer

The correct answer is (c) 1, 2, and 3.

Step 1: Understand the definition of polymers

Polymers are large molecules made from many repeated units, called monomers. This forms a chain-like structure. This matches statement 1, which describes polymers as substances made up of recurring structural units derived from monomers.

Step 2: Differentiate between homopolymers and copolymers

A homopolymer is made from only one type of monomer, whereas a copolymer is made from two or more different types of monomers. Statement 2 correctly defines the difference between homopolymers and copolymers.

Step 3: Determine the relationship between polymers and macromolecules

Polymers are often large molecules or macromolecules, and they typically consist of a mixture of molecules with different molecular weights. This matches statement 3.

Step 4: Compare the given statement sets with the options

Based on the analysis, all statements (1, 2, and 3) are correct. Option (c), which includes all three statements, is the correct answer.

Key Concepts

Monomers

Monomers are the essential building blocks of polymers. Imagine them as individual beads on a string. Each bead, or monomer, is a small molecule that can join together with other monomers to form a larger chain. This process of linking monomers is called polymerization.

• Monomers usually contain a double bond or other reactive sites, allowing them to connect with other monomers.
• Common examples include ethylene, which forms polyethylene, and styrene, which forms polystyrene.

The nature of the monomer determines the properties and applications of the resulting polymer. For instance, polymers made from flexible monomers can be soft and pliable, while those from rigid monomers are hard and strong. With monomers being so crucial, understanding their structure and reactivity helps us predict the behavior of the polymers they form.

Homopolymers

Homopolymers are polymers that consist of only one type of monomer. This results in a uniform structure with each repeating unit being identical. Imagine a long string made entirely from the same type of bead.

• The uniformity allows for more predictable properties and reactions.
• An example of a homopolymer is polyethylene, which is made entirely from ethylene monomers.

Because they are made from a single type of monomer, homopolymers often have consistent properties, making them suitable for specific applications. Their simplicity in structure can lead to ease in processing and recycling. Homopolymers showcase how polymers can vary widely, even when composed of identical repeating units.

Copolymers

Copolymers are formed when two or more different types of monomers come together in a single polymer chain. This combination allows for a diverse range of properties and uses. Imagine a string with beads of different colors and shapes.

• Copolymers can be designed to enhance specific properties that homopolymers might lack.
• They may have blocks of different monomers or alternate in a regular pattern.
• Common examples include nylon and ABS plastic.

By combining different monomers, copolymers can achieve a balance of flexibility, strength, and durability, making them incredibly versatile. Whether used in textiles, automotive parts, or packaging materials, copolymers play a crucial role in everyday applications.

Macromolecules

Polymers are often referred to as macromolecules due to their large molecular size. These large structures are formed by linking thousands or even millions of monomers together.

• The term "macromolecule" highlights the size and complexity of these molecules.
• Examples include DNA, proteins, and synthetic polymers like plastics.
• Polymers may vary in weight, creating a mixture within any given sample.

Understanding macromolecules involves delving into how their large size influences physical properties such as melting point, strength, and durability. The study of macromolecules helps scientists develop new materials that meet specific needs, from stronger materials to biodegradable plastics. By exploring macromolecules, we open the door to innovation in materials science.