GSEB Class 8 Science Solutions Chapter 3 Synthetic Fibres and Plastics

Question 1. Explain why some fibres are called synthetic.
Answer: Some fibres are called synthetic because they do not exist naturally.
In simple words: These fibres are called synthetic because humans make them, and they are not found in nature.

Exam Tip: When explaining 'synthetic', focus on the 'man-made' aspect and their absence in natural environments.

Question 2. Tick (4) the correct answer. Rayon is different from synthetic fibres because:
(a) It has a silk-like appearance.
(b) It is obtained from wood pulp.
(c) Its fibres can also be woven like those of natural fibres.
Answer: (b) It is obtained from wood pulp.
In simple words: Rayon is different because it comes from wood, which is a natural source, even though it feels like silk.

Exam Tip: Remember that rayon is a regenerated fibre, not fully synthetic, as it comes from natural cellulose (wood pulp).

Question 3. Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called or fibres.
(b) Synthetic fibres are synthesised from raw material called .
(c) Like synthetic fibres, plastic is also a
Answer:
(a) man-made, artificial.
(b) Petrochemicals.
(c) polymer.
In simple words: Synthetic fibres are also known as man-made or artificial fibres, created from petrochemicals. Plastics are also a type of polymer.

Exam Tip: Know the alternative names for synthetic fibres and the basic material they are made from, as well as the general classification of plastic.

Question 4. Give examples which indicate that nylon fibres are very strong.
Answer: Nylon fibres are robust, so people use them for crafting parachutes and ropes for rock climbing.
In simple words: Nylon is very tough. Because of its strength, it's perfect for making things like parachutes and rock climbing ropes.

Exam Tip: When asked for examples, choose common items that clearly demonstrate the material's key property, like strength for nylon.

Question 5. Explain why plastic containers are favoured for storing food.
Answer: Advantages of plastic containers include:

• Plastics do not interact with food products.
• Plastics are tough and light in weight.
• They are simple to manage and secure.

Exam Tip: List key benefits like non-reactivity, durability, and convenience when explaining why plastic is good for food storage.

Question 6. Explain the differences between thermoplastics and thermosetting plastics.
Answer: Differences:
Thermoplastics:

• These are plastics that easily change shape when heated and can be simply bent.
• Examples include Polythene and PVC.
• Manufacturers use these for making toys, combs, car grills, and various containers.

• These are plastics that, once shaped, cannot be softened by warming.
• Examples: Bakelite and Melamine.
• (a) Bakelite helps in creating electrical switches, various utensil handles, and similar items.
• (b) Melamines are useful for producing floor tiles, kitchenware, and flame-resistant fabrics.

Exam Tip: Focus on the key difference: reversibility with heat. Thermoplastics can be reshaped; thermosetting plastics cannot after initial molding.

Question 7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Answer:
(a) Saucepan handles are made from thermosetting plastics because these plastics are poor heat conductors and do not become hot during cooking.
(b) Electric plugs, switches, and plug boards are created from thermosetting plastics because they are poor conductors of electricity. Electrical current does not travel through such plastics.
In simple words: Saucepan handles use thermosetting plastic because it doesn't conduct heat well, so they stay cool. Electrical parts use it because it doesn't conduct electricity, making them safe.

Exam Tip: Connect the properties of thermosetting plastics (heat and electrical insulation) to their specific uses in household items.

Question 8. Categorise the materials of the following products into 'can be recycled' and 'cannot be recycled'. Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
Answer: Can be recycled: Toys, carry bags, plastic bowls, ball point pens, plastic chairs, and electric wire covering.
Cannot be recycled: cooker handles, electric switches, and telephone instruments.
In simple words: Items that can be reshaped, like toys and bags, are recyclable. Items that become rigid and can't be reshaped, like cooker handles and electric switches, are not recyclable.

Exam Tip: Generally, thermoplastics are recyclable, while thermosetting plastics are not. Use this rule to categorize plastic items.

Question 9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer: Rana should purchase cotton shirts for summer because cotton is a poor heat conductor. It prevents heat from transferring to or from the body, thereby shielding the body from warmth. Cotton also possesses a greater ability to absorb moisture compared to synthetic clothing. As a result, it holds the body's sweat and helps keep you cool.
In simple words: Rana should get cotton shirts for summer. Cotton keeps you cool because it doesn't let heat pass easily and can soak up sweat, unlike synthetic materials.

Exam Tip: When comparing fabrics for specific weather, discuss thermal conductivity, breathability, and moisture absorption properties.

Question 10. Give examples which indicate that plastics are noncorrosive in nature.
Answer: Plastics exhibit a non-corrosive nature:

• They do not interact with any substance.
• Plastics do not respond to air and water, which are crucial for corrosion.
• They do not display any chemical reactions.

Exam Tip: To demonstrate non-corrosive properties, highlight that plastics do not react with common corrosive agents like air, water, and various chemicals.

Question 11. Should the handle and bristles of a toothbrush be made of the same materials? Explain your answer.
Answer: No, a toothbrush handle and its bristles should not be made from the same material. This is because the handle requires firmness, whereas the bristles need to be soft. The handle should consist of a material that offers a steady grip, and the bristles should comprise a soft material to prevent harm to the teeth.
In simple words: No, the handle and bristles should be different. The handle needs to be hard for a good grip, but the bristles must be soft so they don't hurt your teeth.

Exam Tip: When discussing material choices for tools, consider the specific function of each part and how material properties (hardness, softness, grip) contribute to effective and safe use.

Question 12. 'Avoid plastics as far as possible'. Comment on this advice.
Answer: Plastics are non-biodegradable materials. Therefore, using plastics harms our surroundings. Plastics cannot be fully broken down or gotten rid of. Consequently, we should avoid plastics as much as we can.
In simple words: We should avoid plastics because they don't break down naturally and stay in the environment for a very long time, which is bad for the planet.

Exam Tip: When discussing environmental impact of plastics, emphasize their non-biodegradable nature and the long-term waste problem they create.

Question 13. Match the terms of Column A correctly with the phrases given in Column B.
Answer:

Exam Tip: Learn the specific properties and common uses of different synthetic fibres and plastics to correctly match them.

Question 14. 'Manufacturing synthetic fibres is actually helping conservation of forests'. Comment.
Answer: Natural fibres required their raw materials from plants and animals, which often involved felling trees and harming animals. Synthetic fibres, however, are composed of chemicals created in a laboratory. Therefore, making synthetic fibres genuinely aids in preserving forests.
In simple words: Making synthetic fibres helps save forests because natural fibres need trees to be cut down and animals to be harmed, but synthetic ones are made from chemicals in labs.

Exam Tip: When discussing the environmental impact of synthetic fibres, highlight their role in reducing the demand for natural resources like wood and animal products.

Question 15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer: Examine some electrical wires. They possess a plastic coating, which does not transmit electricity. Additionally, screwdriver handles are constructed from plastic. These observations demonstrate that plastics serve as poor conductors of electricity.
In simple words: Look at electrical wires and screwdriver handles. Both have plastic on them because plastic doesn't let electricity pass through, showing it's a bad conductor.

Exam Tip: When providing an activity to demonstrate conductivity, use real-world examples that clearly illustrate the material's properties, like plastic coatings on wires.