Synthetic fibres and plastics class 8 Science NCERT Solutions

Synthetic fibres and plastics class 8 Science NCERT Solutions: Synthetic fibres and plastics is the chapter 3 from class 8 Science NCERT. Here you'll get Synthetic fibres and plastics class 8 Science/Synthetic fibres and plastics class 8 Science NCERT Solutions.

Synthetic fibres and plastics class 8 Science Main Points

Synthetic fibres and plastics, like natural fibres, are made of very large units called polymers. Polymers are made up of many smaller units.

While natural fibres are obtained from plants and animals, synthetic fibres are obtained by chemical processing of petrochemicals. Like natural fibres, these fibres can also be woven into fabrics.

Synthetic fibres find uses ranging from many household articles like ropes, buckets, furniture, containers, etc., to highly specialised uses in aircrafts, ships, space-crafts, healthcare, etc.

Depending upon the types of chemicals used for manufacturing synthetic fibres, they are called Rayon, Nylon, Polyester and Acrylic.

The different types of fibres differ from one another in their strength, water absorbing capacity, nature of burning, cost, durability etc.

Today, life without plastics cannot be imagined. Be it home, or outside, plastic is everywhere. The waste created by plastics is not environment friendly. On burning, plastics release poisonous gases. On dumping in the ground they may take years to degenerate. This is because of their non-biodegradable nature.

We need to use synthetic fibres and plastics in such a manner that we can enjoy their good qualities and at the same time minimise the environmental hazards for the living communities.

Nylon appears like silk. It is strong and flexible. These endearing qualities of nylon created a public sensation, or nylon mania, when it was introduced in 1939.

Women’s stockings made from this new fibre were in great demand. But, unfortunately, most of the nylon production had to be diverted to making parachutes during the Second World War (1939-1945).

After the war, when production of stockings resumed, supply did not match the demand. There was a huge black market for this product. Women had to wait for hours in queues to get a pair. Often there were nylon riots.

Synthetic fibres and plastics class 8 Science Notes

The different types of clothes which we wear are made of fabrics. These fabrics are made from different types of fibres. There are two types of Fibres –

Natural Fibre and
Synthetic fibre.

Natural fibres are those which are obtained from plants and animal sources. They include cotton, jute, silk, wool, etc. Synthetic fibres are those which are man-made and are obtained by the combination of different types of chemical substances and raw materials such as petrochemicals.

They include nylon, acrylic, polyester and so on. These fibres are also called artificial or man-made fibres. There are 4 different types of Synthetic fibre.

Rayon: It is synthesized from wood pulp and is dyed using different colours. It is also called artificial silk as it resembles silk. Rayon is cheaper than silk.

Nylon: It is the first commercially synthesized fibre. It is synthesised by using coal, water and air. Nylon is very strong and its fabric resembles silk.

Polyester: It is one of the most popular man-made fibres, which is widely used for making clothes. Polyesters are generally made of repeating unit of a chemical called esters.

Acrylic: It is a man-made fibre which is known as artificial wool or synthetic wool as it resembles wool. Compared to natural wool, Acrylic is much cheaper and it can be dyed by various colours.

Plastics are polymers that can be coloured, recycled, reused, mould and can be drawn into wires or various other shapes. They are mainly used in making bags, brush, chairs, tables, toys, and many other countless items. Polythene is one of the most famous types of plastic, which is used in the manufacturing of carrying bags.

Class 8 Science Chapter 3 Synthetic fibres and plastics Questions Answers

1. Explain why some fibres are called synthetic.

Ans: Some fibres are called synthetic because these are manmade fibers prepared by using chemicals. These are made of small units that join together to form long chains. Some of the examples of synthetic fibres are nylon, rayon, acrylic, polyester etc.

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.

Ans: Rayon is different from synthetic fibres because it is obtained from wood pulp.

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 __________ .

Ans:

(a) Synthetic fibres are also called artificial or man-made fibres.

(b) Synthetic fibres are synthesised from raw materials called petrochemicals.

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

Ans: The following examples indicate that nylon fibres are very strong.

(i) They are used for making parachutes and ropes for rock climbing.

(ii) They are used in making seat-belts, fishing nets, tyre cord.

(iii) Nylon is used in making sports accessories like rackets and musical instruments.

5. Explain why plastic containers are favoured for storing food.

Ans: Plastic containers are favoured for storing food because of

(i) the plastics do not react with the food stored in them.

(ii) the plastics are lightweight and are strong.

(iii) they are easy to handle and safe.

6. Explain the difference between thermoplastic and thermosetting plastics.

Ans:

Thermoplastics:

(i) They do not lose their plasticity.

(ii) These plastics softened on heating and can be bent easily.

(iii) Examples are polythene, PVC, etc.

Thermosetting plastics

(i) They lose their plasticity.

(ii) These plastics when moulded once, can’t be softened again.

(iii) Examples are bakelite and melamine.

NCERT Solutions of Synthetic fibres and plastics class 8 Science

7. Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

(b) Electric plugs/switches/plug boards

Ans:

(a) The saucepan handles are made of thermosetting plastics because they are bad conductors of heat. So they do not get heated up while cooking and can be handled easily. In addition to this, thermosetting plastics do not get softened on heating.

(b) Electrical plugs, switches and plug-boards are made up of thermosetting plastics because they are bad conductors of electricity. So, they do not allow the electric current to pass through them are thus safe to touch.

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.

Ans: Can be recycled Cannot be recycled

plastic toys telephone instruments

carry bags cooker handles

plastic bowls ball point pens

plastic covering on electrical wires electrical switches

plastic chairs

9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material ? Advise Rana, giving your reason.

Ans: He should buy cotton shirts. This is because cotton has more capacity to hold moisture than synthetic clothes. Cotton is a good absorber of water, in summers we have extensive sweating which is easily soaked by cotton shirts and thus, cotton clothes are much better than the clothes made from synthetic material.

10. Give examples to show that plastics are noncorrosive in nature.

Ans: Plastics are noncorrosive in nature, some of the examples that shows are;

(i) Plastic containers do not react with items stored in it.

(ii) Plastic do not get rusted when exposed to moisture and air.

(iii) Plastic not decompose when left in open for a long period.

11. Should the handle and bristles of a tooth brush be made of the same material ? Explain your answer.

Ans: The handle and bristles of a tooth brush should be made of different materials. Because the handle of a toothbrush should be hard and strong, while the bristles should be soft and flexible.

12. ‘Avoid plastics as far as possible’. Comment on this advice.

Ans: Plastics must be avoided as far as possible. The materials made of plastics are non-biodegradable. The use of plastics has a bad effect on the environment. They lead to air pollution as on burning they release poisonous gases into the atmosphere. Also, the plastic bags thrown in garbage if swallowed by animals can choke their respiratory system and even lead to their death. Plastics bags thrown carelessly can also cause clogging of the drains.

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

A 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 cook wares

(iv) Nylon (d) Fabrics do not wrinkle easily

Ans: A B

(i) Polyester (d) Fabrics do not wrinkle easily

(ii) Teflon (c) Used to make non-stick cook wares

(iii) Rayon (a) Prepared by using wood pulp

(iv) Nylon (b) Used for making parachutes and stockings

14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Ans: In the manufacturing of synthetic fibres only chemical substances are used. Thus, the manufacturing of synthetic fibres has reduced the cutting of trees or hunting of animals. In this way manufacturing synthetic fibres is actually helping conservation forests.

NCERT Solutions for Synthetic fibres and plastics class 8 Science

15. Describe an activity to show that thermoplastic is a poor conductor of electricity.

Ans: In order to show that thermoplastic is a poor conductor of electricity, For that, we need a bulb, some wires, a battery, a piece of metal and a plastic pipe.

The following activity can show that thermoplastic is a poor conductor of electricity:

We will design a circuit to show that thermoplastics are poor conductors of electricity.

(i) We will make two circuits - one with the metal and other with the plastic pipe.

(ii) After switching on the circuit, you will observe that the bulb in the circuit with metal starts glowing whereas in the other circuit with plastic pipe bulb does not glow.

This proves that the plastic pipe which is a thermoplastic is a poor conductor of electricity.