Science Class 8– Chapter 3- Synthetic Fibres and Plastics- NCERT Exercise Solutions (Question-Answer) provided below. Total there are 15 Questions. All are solved here.
Exercise with Answer –
Q1.Explain why some fibres are called synthetic.
Answer – Some fibres are called synthetic because they are made by human beings using some chemical substances. These are made by joining small units called monomers into long chains.
Q.2Mark(tick) 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.
3. Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called ___________ or ___________fibres.
Answer – manmade, artificial
(b) Synthetic fibres are synthesised from raw material called __________.
Answer – petrochemical
(c) Like synthetic fibres, plastic is also a ____________.
Answer- polymer.
Q4. Give examples which indicate that nylon fibres are very strong.
Answer – Nylon is man-made fibre. It is strong, elastic and light.
There are some reason which indicates the nylon fibre is very strong:-
(i) Nylon is used for making parachutes and ropes for rock climbing.
(ii) They are used for making ropes, tents, seat belts, sleeping bags, etc.
Q5. Explain why plastic containers are favoured for storing food.
Answer – Plastic containers are favoured for storing food because they don’t react with water and air. Plastic is very light, strong, and durable. They don’t react with food.
Q6. Explain the difference between thermoplastic and thermosetting plastics.
Answer – There are some difference between thermoplastic and thermosetting plastics-
| Thermoplastic | Thermosetting |
| They got deformed and easily on heating.
They do not lose their plasticity. They used to make toys, comb etc. Polythene, PVC | They cannot be softened by heating when moulded once.
They lose their plasticity. They are used for making electrical switched, handles of various utensils etc. eg. Melamine, bakelite |
Q7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
Answer – Saucepan handles are made of thermosetting plastics because thermosetting plastics are poor conductor of heat.
(b) Electric plugs/ switches / plugboards
Answer – Electric plugs/switches/plug boards are made of thermosetting plastic are poor conductor of electricity. It doesn’t allow to pass an electric current.
Q8. 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.
Answer –
Telephone instruments —–> Cannot be recycled
plastic toys ———–> can be recycled
cooker handles ——–> cannot be recycled
carry bags ———-> can be recycled
ballpoint pens ———> cannot be recycled
plastic bowls ——-> can be recycled
plastic covering on electric wires —–> can be recycled
plastic chairs —–> can be recycled
Electric switches ——-> cannot be recycled
Q9. 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 because cotton holds moisture and can easily soak our sweating.
Q10. Give examples to show that plastics are noncorrosive in nature.
Answer – Some examples which show that plastics are non-corrosive in nature. It means do not get destroyed by the chemical action.
Plastic containers don’t react with stored food in it.
Plastics not get rusted like iron when left exposed to moisture and air.
Plastics are non-biodegradable.
Q11. Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.
Answer – No, the handle and bristles of a tooth-brush are not made of the same material because the handle of tooth-brush is hard and strong, and it is made from plastic. But, bristles of the toothbrush are soft and made from nylon.
Q12. ‘Avoid plastics as far as possible’. Comment on this device.
Answer – We should have to avoid plastic as far as possible because it is harmful to our environment. Plastics are non-biodegradable. So, it can not decompose easily. It causes environmental pollution.
After burning, it releases poisonous gas.
If there were plastics are thrown in the garbage and eaten by animal-like a cow. These bags choke their respiration system and can prove fatal.
Q13. 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 cookware |
| (iv) Nylon | (d) Fabrics do not wrinkle easily |
Answer –
| A | B |
| (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 |
Q14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
Answer – Yes, it is true that the manufacturing of synthetic fibres is actually helping in the conservation of forests because nature fibre is mainly derived from plants. This means cutting a lot of trees, which leads to deforestation. But, synthetic material is petrochemical. It is made of the chemical.
Q15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer – We take an example of an electric circuit which shows that thermoplastic is a poor conductor of electricity.
Material required– bulb, wire, battery, piece of metal, plastic pipe.
Procedure :
Set up the circuit first with metal and then with plastic pipe shown in the figure given below.
After we switch on the current, we will observe that the bulb does not glow when there is plastic. Hence, plastic pipe ( which is thermoplastic) is a poor conductor of electricity.
Finally Science Class 8– Chapter 3- Synthetic Fibres and Plastics- NCERT Exercise Solutions (Question-Answer) Ended 👍 👍 👍 👍
Teriful
It’s very good.