Problem 95 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is/are correct about kevlar here? (I) It is a polyamide (II) It is used in making buluet proof vests etc III) It is homopolymer formed by addition reaction. IV) It is polymer of terephthalic acid and 1,4 diamino benzene. (a) I, II, III (b) I, II, IV (c) II, III, IV (d) I, II, III, IV

Step-by-Step Solution

Answer

The correct answer is (b) I, II, IV.

Step 1: Analyze Statement I

Kevlar is a polyamide, meaning it contains amide bonds (-CONH-) that link its monomer units. Polyamides are polymers made from the reaction between a diamine and an acid, typically with the elimination of water. Thus, Statement I is correct.

Step 2: Evaluate Statement II

Kevlar is known for its high strength and durability. One of its primary uses is in the production of bulletproof vests due to its ability to absorb and dissipate energy, thereby providing protection. Therefore, Statement II is correct.

Step 3: Investigate Statement III

A homopolymer is a polymer that is made from a single type of monomer, while addition reactions involve the joining of monomers without the loss of any small molecules. Kevlar is not a homopolymer; it is a copolymer made from two different monomers. Additionally, it is formed through a condensation reaction rather than an addition reaction. Hence, Statement III is incorrect.

Step 4: Verify Statement IV

Kevlar is indeed a polymer formed by the condensation polymerization of 1,4-diamino benzene and terephthalic acid. These two compounds react to form the characteristic amide bonds of Kevlar. Thus, Statement IV is correct.

Step 5: Determine Correct Options

Based on the analysis, Statements I, II, and IV are correct. Therefore, the correct option that includes all these statements is (b) I, II, IV.

Key Concepts

Polymers

Polymers are large molecules formed by the repeated linking of smaller units called monomers.
Think of them as long chains or networks, where each link in the chain is a monomer.
In organic chemistry, this formation is crucial for creating a variety of materials, from plastic to proteins.

• Types of Polymers: Polymers are often classified into homopolymers and copolymers.
  Homopolymers consist of only one type of monomer repeated over and over, while copolymers are made up of two or more different types of monomers.
• Properties: The properties of the resulting polymer depend on the type and arrangement of the monomers.
  For example, some polymers like Kevlar are incredibly strong, which makes them useful in protective gear like bulletproof vests.

Understanding polymers is essential because they are everywhere—from the nylon in your clothing to the DNA in your cells.

Condensation Reactions

A condensation reaction in organic chemistry is a process where two molecules join together and, in the process, lose a small molecule, like water.
This type of reaction is crucial for creating many types of polymers.

• Reaction Process: In a typical condensation reaction, each monomer contributes a part of the lost small molecule. For example, when forming an amide bond, an amine group (-NH₂) and a carboxylic acid group (-COOH) combine, releasing a molecule of water (H₂O).
• Polymer Formation: Many essential polymers, such as polyesters and polyamides, are formed through condensation reactions. During this reaction, step-growth polymerization often uses these condensation methods to build complex structures with unique properties.
• Versatile and Functional: The condensation reaction not only links monomers but introduces functional groups (like amides or esters) that can affect the final polymer's properties, such as solubility, strength, and flexibility.

Condensation reactions are a fundamental concept in polymer chemistry, driving the formation of diverse materials.

Polyamides

Polyamides are a type of polymer characterized by the presence of recurring amide groups in the backbone of the polymer chain.
They are formed through the polymerization of monomers like diamines and dicarboxylic acids in a condensation reaction.

• Structure: The key feature of polyamides is the amide bonds (-CONH-) that link the monomer units. These bonds are similar to the peptide bonds that hold proteins together, giving polyamides their remarkable strength.
• Examples: Common examples include not only Kevlar, which is known for its use in bulletproof vests, but also nylon, often used in textiles and engineering materials.
• Properties: Polyamides are valued for their strength, durability, and resistance to wear and tear.
  They are used in applications where high mechanical strength and stability are required, such as automotive and aerospace components.

The unique properties of polyamides make them invaluable in both everyday products and specialized applications.