Synthetic Fibres and Plastics Class 8 Questions Answers Explained

What Are Synthetic Fibres and How Are They Made?

Synthetic fibres are fibres made by humans through chemical processes, unlike natural fibres which come from plants or animals. These fibres are created by polymerisation, where small molecules called monomers join to form long chains called polymers.

Common synthetic fibres include nylon, polyester, and acrylic. They are widely used in textiles because of their strength, durability, and resistance to water and insects.

How Synthetic Fibres Are Made

• Raw materials (usually from petroleum) are processed chemically.
• Polymerisation creates long polymer chains.
• These polymers are melted and extruded through spinnerets to form fibres.

Example: Nylon is made by joining hexamethylenediamine and adipic acid to form a polymer called nylon-6,6.

Synthetic fibres have advantages such as quick drying, wrinkle resistance, and easy maintenance, making them popular in clothing and home furnishings.

Understanding Plastics: Types and Uses

Plastics are synthetic materials made from polymers that can be moulded into different shapes when heated. They are widely used in packaging, household items, toys, and medical equipment.

Types of Plastics

Thermoplastics like polyethylene and polystyrene can be reshaped multiple times, making them easier to recycle. Thermosetting plastics like bakelite are heat resistant and strong but cannot be remoulded.

Common Plastics and Their Uses

• Polyethylene: bags, containers
• Polyvinyl chloride (PVC): pipes, cables
• Bakelite: electrical switches

Plastics have revolutionised many industries but improper disposal causes environmental issues.

Differences Between Natural and Synthetic Fibres

Understanding the differences between natural and synthetic fibres helps in answering many Class 8 Science questions.

Natural fibres are biodegradable but less durable, while synthetic fibres last longer but are not biodegradable. Both have their own uses in textiles and industry.

Common Questions on Synthetic Fibres and Plastics with Answers

Here are some important questions and answers to help Class 8 students prepare for exams:

Q1: What is polymerisation?

Polymerisation is the chemical process where small molecules called monomers join to form long chains called polymers, which make synthetic fibres and plastics.

Q2: Name two synthetic fibres and their uses.

Nylon (used in parachutes, ropes) and polyester (used in clothing, bottles).

Q3: Why are synthetic fibres preferred over natural fibres in some cases?

Because they are stronger, resist water and insects, and dry quickly.

Q4: What is the difference between thermoplastics and thermosetting plastics?

Thermoplastics soften on heating and can be reshaped; thermosetting plastics harden permanently and cannot be reshaped.

Q5: How can plastics be recycled?

Plastics can be melted and remoulded (thermoplastics) or chemically processed to reduce waste and pollution.

Worked Example: Calculating Polymer Chain Length

Let’s understand polymerisation with a simple example.

Example: If one monomer unit has a molecular weight of 50 g/mol and a polymer chain contains 1000 such units, calculate the molecular weight of the polymer.

Solution:

Molecular weight of polymer = Number of units × Molecular weight of one unit

$$ = 1000 \times 50 = 50,000 \text{ g/mol} $$

This shows how large and heavy polymers can be compared to their monomers, explaining their strong material properties.

Such calculations help in understanding the scale of synthetic fibres and plastics at the molecular level.

Tips for Answering Synthetic Fibres and Plastics Class 8 Questions

To score well in exams, follow these tips:

• Read NCERT textbook thoroughly, focusing on definitions and examples.
• Practice all questions at the end of the chapter.
• Use diagrams to explain fibre and plastic structures.
• Remember key differences using comparison tables.
• Write answers clearly and concisely.
• Revise important terms like polymerisation, thermoplastics, and thermosetting plastics.

Consistent practice with solved examples and questions will build confidence and improve your understanding.