RBSE Solutions for Class 8 Science Chapter 3 Synthetic Fibres and Plastics

Rajasthan Board RBSE Solutions for Class 8 Science Chapter 3 Synthetic Fibres and Plastics Textbook Exercise Questions and Answers.

RBSE Class 8 Science Solutions Chapter 3 Synthetic Fibres and Plastics 

RBSE Class 8 Science Synthetic Fibres and Plastics InText Questions and Answers

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Question 1. 
Is nylon fibre really so strong that we can make nylon parachutes and ropes for rock climbing?
Answer:
Yes, the fibre of nylon is very strong and a nylon wire is stronger than steel wire so we can make nylon parachutes and ropes for rock climbing.

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Question 2. 
My mother always buys PET bottles and PET jars for storing rice and sugar. I wonder what PET is!
Answer:
PET (polyethylene terephthalate) is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.
 

RBSE Class 8 Science Synthetic Fibres and Plastics Textbook Questions and Answers 

Question 1. 
Explain why some fibres are called synthetic?
Answer:
Some fibres are called synthetic because these are man made artificial fibres. These fibres are prepared by chemical processes.

Question 2. 
Mark (√ ) 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.

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) artificial, man made
(b) petrochemicals
(c) polymer 

Question 4. 
Give examples which indicate that nylon fibres are very strong.
Answer:

• Patachutes 
• Ropes for rock climbing are prepared from nylon which indicate that nylon fibres are very strong.

Question 5. 
Explain why plastic containers are favoured for storing food.
Answer:
Plastic containers are favoured for storing food due to these reasons.

• They do not react with food, water and air.
• They are strong and light.
• They are durable.

Question 6. 
Explain the difference betwen thermoplastic and thermosetting plastics.
Answer:

Thermoplastic	Thermosetting plastic
The plastic which gets deformed easily on heating and can bend easily is known as thermoplastic.	The plastic which gets moulded once, can not be softened on heating is called thermosetting plastic.
Examples- Polythene and Polyvinyl chloride (PVC)	Examples- Bakelite and melamine

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 of thermosetting plastics (bakelite) because this is bad conductor of heat.
(b) Electric plugs/switches and plug boards are also made of thermosetting plastics (bakelite) because this is bad conductor of electricity.

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:

1. Materials which can be recycled are: plastic toys, carry bags, ball point pens, plastic bowls, plastic covering on electric wires and plastic chairs.
2. Materials which can not be recycled are: telephone instruments, cooker handles, electrical switches.

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 buy cotton shirts for summer because:

1. Cotton cloth is bad conductor of heat so outer heat will not enter in our body, therefore this will protect our body from heat.
2. Cotton cloth can absorb sweat excreted from our body so our body remains cool, but synthetic shirts do not absorb sweat and are not porous.

Question 10. 
Give examples to show that plastics are non corrosive in nature ?
Answer:
Plastics do not react with water and air so they are not corroded easily, therefore plastics are non corrosive in nature.

Examples -

• Several chemicals are stored in plastic bottles.
• They are also used in the storage of different types of foods because they do not react with food.
• Pickles and water are also stored in plastic containers.

Question 11. 
Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Answer:
Handle and bristles of a tooth brush should not be of the same material. Bristles should be soft, flexible and strong while handle should be slightly hard and strong.

Question 12. 
‘Avoid plastics as far as possible’. Comment on this advice.
Answer:
Plastic is non biodegradable because it takes several years to decompose and it is not environment friendly. It causes environmental pollution. Besides die burning process of the synthetic material, is quite slow and it does not get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution. So avoid the use of plastics as far as possible.

Question 13. 
Match the terms of column A correctly with the phrases given in colunm B.

Column A	Column B
(i) Polyester	(a) Prepared by using wood pulp
(ii) Teflon	(b) Used for making parachutes and stockings
(iii) Rayon	(c) Used to make non-stick cookwares
(iv) Nylon	(d) Fabrics do not wrinkle easily

Answer:

Column A	Column B
(i) Polyester	(d) Fabrics do not wrinkle easily
(ii) Teflon	(c) Used to make non-stick cookwares
(iii) Rayon	(a) Prepared by using wood pulp
(iv) Nylon	(b) Used for making parachutes and stockings

Question 14. 
"Manufacturing synthetic fibres is actually helping conservation of forests". Comment.
Answer:
Manufacturing synthetic fibres is actually helping conservation of forests because cuttings of trees and hunting of animals is not required for this. Synthetic fibres are made by chemicals and these are not obtained from forests but prepared artificially.

Question 15. 
Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer:
1. Prepare an electric circuit according to the diagram.
2. Put the thermoplastic which is to be tested between terminal A and terminal B, as shown in the diagram -

3. When circuit is completed the bulb does not spark but when thermoplastic is removed bulb sparks. It proves that thermoplastic is bad conductor of electricity.