NCERT Class 8 Science Chapter 3 Solution​

NCERT Class 8 Science Chapter 3 Solution

Brief Information: This post contains the solution for Chapter 3 Synthetic Fibres and Plastics of Class 8 of the CBSE and Gujarat Board (GSEB) books by GCERT (based on new NCERT)

Q1. Explain why some fibres are called synthetic.

Ans. Fibres like silk, cotton and jute are obtained from the nature. But many fibres are made by human beings. These fibres are called Synthtic fibres or man-made fibres to differentiate them from the natural fibres. e.g. nylon, polyester, rayon.

Q.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.
Ans.
(b) it is obtained from wood pulp.


Q.3. Fill in the blanks with appropriate words.

(a) Synthetic fibres are also called Man-made or Synthetic fibres.
(b) Synthetic fibres are synthesised from a raw material called
petrochemicals.
(c) Like synthetic fibres, plastic is also a
polymer.

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

Ans. Nylon is the first synthetic or man-made fibre. Nylon is stronger than a steel wire. Its strength is indicated by its use in 
a.) Making socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains, etc.
b.) Making parachutes and ropes for rock climbing.

 

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

Ans. Plastic containers are favoured for storing food because of their quality like
a.) Non-reactivity – with the food materials.
b.) Light weight and durability which makes it easy to carry around and they last for long time.
c.) They are lower in price and easy to handle.

 

Q.6. Explain the difference between thermoplastic and thermosetting plastics.

Thermoplastics

Thermosetting plastics

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

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

b.) They do not lose their plasticity.

b.) They lose their plasticity.

c.) E.g. polyethene, PVC, etc.

c.) E.g. bakelite and melamine.

d.) These are used for manufacturing toys, combs and various types of containers.

d.) It is usedfor making floor tiles, kitchenware and fabrics which resist fire.

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

(a) Saucepan handles
Ans. Thermosetting plastics are a bad conductor of heat and do not get heated up while cooking. Thus, they are used for making saucepan handles.

(b) Electric plugs/switches/plugboards

Ans. Thermosetting plastics are a bad conductor of electricity and the electric current does not pass through such plastics. Thus, they are used for making electric plugs/switches/plugboards.

Q.8. Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.

Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Ans.

Can be Recycled

Cannot be Recycled

Plastic toys carry bags

Telephone instruments

Plastic bowls

Cooker handles

Plastic covering on electrical wires

Ballpoint pens

Plastic chairs

Electrical switches

Q.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. In summers the temperature of environment is very high. We sweat extensively. The cotton cloth socks more sweat compared to the synthetic cloth. So, Rana should be adviced to buy cotton shirt for summer.

Q.10. Give examples to show that plastics are non-corrosive in nature.

Ans. Non-corrosive materials are the one which do not get affect/damaged by the chemical action. In other words, they are resistant to action of chemical agents. Plastic is non-corrosive in nature. It is show by below examples:
a.) Plastic containers do not react with items stored in it.
b.) They do not get rusted when exposed to moisture and air.
c.) They do not decompose when left in open for a long period.

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

Ans. Our gums are made of sensitive skin. It cannot resist heavy friction. Brushing hard materials can lead to bleeding from gums. The bristles of toothbrush should be made of soft material. The handle requires strength to be held upright. It should be made of Hard and strong material. It can be concluded from above observation that the handle and bristles of a toothbrush cannot be made from the same material.

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

Ans. Plastics are man-made/synthetic material which takes several year to decompose. If burnt, it produces poisonous fumes/gases which cause air pollution. Sometimes, animals eat the plastic waste. It chokes their respiratory system, or forms a lining in their stomachs and can be the cause of their death. The plastic bags and wrappers of chips, biscuits and other eatables are thrown on road side. They clog the drainage system and are responsible for formation of water ponds on roads of city.  Due to its bad effect on environment, the use of plastic should be avoided. Natural products such as cotton and jute bags should be used instead of plastic bags.

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

GCERT Class 8 Science Chapter 3 Solution

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

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

Ans. Before invention of synthetic fibres, most of the resources used by man were obtained from the nature, particularly forests. For instance wide regions forest were cleared to obtain timber, make card-box, fibre and cultivation of fibre crops. Synthetic fibres are stronger and durable than natural based products. They are completely made from the chemicals. The benefits of synthetic fibres has reduced the utility of forest based products. Thus, Manufacturing synthetic fibres is actually helping the conservation of forests.

NCERT Class 8 Science Chapter 3 Solution​
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