Problem 69 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following pairs is not correctly matched? (a) Teflon: Thermally stable cross linked polymer of phenol and formaldehyde (b) Synthetic rubber: A copolymer of butadiene and styrene (c) Terylene: Condensation polymer of terephthalic acid and ethylene glycol (d) Perspex: A homopolymer of methyl methacrylate

Step-by-Step Solution

Answer

Option (a): Teflon is not correctly matched.

Step 1: Understand Each Pair

Read through each option to understand which polymers and their descriptions have been paired together. 1. Teflon - Described as a thermally stable cross-linked polymer of phenol and formaldehyde. 2. Synthetic rubber - Described as a copolymer of butadiene and styrene. 3. Terylene - Described as a condensation polymer of terephthalic acid and ethylene glycol. 4. Perspex - Described as a homopolymer of methyl methacrylate.

Step 2: Verify the Descriptions

Check the descriptions of polymers: 1. Teflon is actually a polymer of tetrafluoroethylene, not a cross-linked polymer of phenol and formaldehyde. Phenol and formaldehyde produce Bakelite. 2. Synthetic rubber (SBR) is correctly described as a copolymer of butadiene and styrene. 3. Terylene is rightly described as a condensation polymer of terephthalic acid and ethylene glycol, known as PET or polyester. 4. Perspex is correctly identified as a homopolymer of methyl methacrylate (also known as PMMA).

Step 3: Identify the Incorrect Pair

Identify which pair does not match their description from the information verified in Step 2. The incorrect pair is: Teflon and cross-linked polymer of phenol and formaldehyde.

Step 4: Conclude

From the analysis in previous steps, option (a) is not correctly matched since Teflon is not a product of phenol and formaldehyde. In contrast, the other pairs were correctly identified with their respective polymer descriptions.

Key Concepts

Polymers

Polymers are large molecules made up of repeating units called monomers. These monomers are chemically bonded to form chains, which can vary in length and composition. Polymers play an essential role in everyday materials due to their versatile properties. They can vary from flexible and elastic to firm and rigid, depending on their molecular structure.
Different types of polymers include:

• Homopolymers: Made from one type of monomer. Perspex, for example, is a homopolymer derived from methyl methacrylate.
• Copolymers: Formed from two or more different monomers. An example is synthetic rubber, a copolymer of butadiene and styrene.
• Condensation Polymers: Result from the joining of monomers with the elimination of small molecules like water. Terylene, a condensation polymer of terephthalic acid and ethylene glycol, is a common example.

Understanding these basic types helps in identifying and matching polymers with their respective descriptions.

Matching Pairs Question

In matching pairs questions, students are required to pair items from two groups based on their relationships. This type of question is common in exams like JEE Main Chemistry. It tests students' understanding and recall of specific concepts, such as polymer structures and compositions.
To successfully answer matching pairs questions like the given exercise, follow these steps:

• Carefully read each pair and its description.
• Cross-check the definitions and characteristics of each element in the pair.
• Identify any discrepancies between the name and its description.

In our exercise, the task was to find which polymer name and description did not match. By evaluating each pair against known polymer chemistry, the incorrect match could be identified as Teflon, based on a wrong description given here.

Polymer Descriptions

Identifying polymers correctly requires a good grasp of their descriptions and chemical properties. This is crucial for questions where matching polymer names and their descriptions is a must. Let's delve into the example given in the exercise:

• Teflon: This polymer is scientifically recognized as polytetrafluoroethylene (PTFE), known for its non-reactive and non-stick properties, not made from phenol and formaldehyde.
• Bakelite: Often confused with Teflon in descriptions. Bakelite is the product of phenol and formaldehyde, a thermally stable and cross-linked polymer.
• Synthetic Rubber (SBR): A material made by copolymerizing styrene and butadiene, offering elasticity commonly used in tires.
• Terylene: Known as polyester, is a condensation polymer formed from terephthalic acid and ethylene glycol, used in fabrics.
• Perspex (PMMA): Recognized for its transparency and durability, made from the polymerization of methyl methacrylate.

Correctly associating these descriptions with their polymer names is key to identifying mismatched pairs like in the question presented.