Problem 4 - A Complete Resource Book in Chemistry for JEE Main

Question

The repeating units of PTFE are (a) \(\mathrm{F}_{2} \mathrm{C}=\mathrm{CF}_{2}\) (b) \(\mathrm{FCl} \mathrm{C}=\mathrm{CF}_{2}\) (c) \(\mathrm{F}_{3} \mathrm{C}-\mathrm{CF}_{3}\) (d) \(\mathrm{Cl}_{2} \mathrm{CH}-\mathrm{CH}_{3}\)

Step-by-Step Solution

Answer

The repeating unit of PTFE is (a) \( \mathrm{F}_{2} \mathrm{C}=\mathrm{CF}_{2} \).

Step 1: Understand PTFE Structure

PTFE stands for Polytetrafluoroethylene. It's a polymer made up of repeating units of 7 aligned along the polymer chain.

Step 2: Identify the Monomer Unit

The monomer unit for PTFE is tetrafluoroethylene, which has the chemical formula 7. This monomer has two carbon atoms each bonded to two fluorine atoms and a double bond between the carbon atoms.

Step 3: Compare Given Options with PTFE Monomer

Examine each option to check which one matches the formula of tetrafluoroethylene: - Option (a) 7 matches the monomer structure and formula. - Option (b) and others do not match as their structures and elements differ from tetrafluoroethylene.

Step 4: Determine the Correct Answer

Since option (a) 7 has the same formula and structure as the repeating unit of PTFE, it is the correct answer.

Key Concepts

Polytetrafluoroethylene

Polytetrafluoroethylene, commonly known as PTFE, is a synthetic polymer renowned for its non-stick and heat-resistant properties.
This makes it a popular material in cookware, electrical insulation, and even in the aerospace industry. PTFE consists of long chains of repeating tetrafluoroethylene units, which we can think of like links in a chain.
The non-stick nature of PTFE is due to its molecular structure; fluorine atoms create a slick, slippery surface that prevents adherence.

• Properties: PTFE is resistant to high temperatures and chemical reactions.
• Applications: Used in non-stick cookware, as well as plumbing tape and laboratory equipment.

Understanding PTFE's structure helps us see why it does not react easily with other substances, making it safe to use in many environments.

Tetrafluoroethylene

Tetrafluoroethylene is a fundamental building block used to make PTFE. Chemically speaking, tetrafluoroethylene is a gas at room temperature, characterized by its formula \(\text{F}_2\text{C}=\text{CF}_2\).
The double bond between its carbon atoms is a pivotal part of its molecular structure, contributing to the polymerization process that forms PTFE.
Tetrafluoroethylene polymerizes, or links together in a chain, under specific conditions. These conditions involve heat and pressure, triggering the carbon-carbon double bond to open up and connect with adjacent monomers.

• Monomer Complexity: Though simple in structure, the polymerization of tetrafluoroethylene creates complex and stable polymers.
• Safety Note: As a precursor in producing non-stick coatings, it is significant to handle tetrafluoroethylene carefully because it is highly reactive.

Appreciating tetrafluoroethylene's role helps us understand the simplicity yet effectiveness of PTFE's impressive features.

Polymer Chemistry

Polymer chemistry is the branch of chemistry that examines large molecules made up of repeating smaller units known as monomers.
These polymers can be natural, like proteins, or synthetic, like PTFE. In polymer chemistry, crucial concepts include the types of polymerization, which determine how monomers bond to form polymers.
There are two main types: addition polymerization, like that used to create PTFE, and condensation polymerization, which releases by-products such as water.

• Addition Polymerization: This involves monomers forming a polymer through the successive addition, like links in PTFE.
• Branching and Cross-Linking: Polymers vary in strength and flexibility depending on how their chains are arranged and linked.

Polymer chemistry explains why materials like PTFE have such diverse applications, from cookware to advanced scientific instruments. It combines the knowledge of chemistry with the practical needs of technology, enabling the development of materials tailored to specific uses.