NCERT Solutions Class 8th Science Chapter – 3 Synthetic Fibers and Plastics Question Answer

Question 1. Explain why some fibres are called synthetic.
?‍♂️Answer: Some fibres are called synthetic fibres because they are made by man using chemicals.

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 a raw material called _____
(c) Like synthetic fibres, plastic is also a _____
?‍♂️Answer:
(a) man-made, artificial fibres
(b) petrochemicals
(c) polymer

Question 4. Give examples which indicate that nylon fibres are very strong.
?‍♂️Answer: 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, a string for sports rackets and musical instruments.

Question 5. Explain why plastic containers are favoured for storing food.
?‍♂️Answer: Plastic containers are favoured for storing food because of the following reasons:

(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.

Question 6. Explain the difference between thermoplastic and thermosetting plastics.
?‍♂️Answer:

Question 7.Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
?‍♂️Answer: Since, thermosetting plastics are a bad conductor of heat and do not get heated up while cooking, they are used for making saucepan handles.

(b) Electric plugs/switches/plugboards
?‍♂️Answer: Since thermosetting plastics are a bad conductor of electricity and the electric current does not pass through such plastics, they are used for making electric plugs/switches/plugboards.

Question 8. Categorise the materials of the following products into ‘can be recycled’ and ‘can not be recycled’.
?‍♂️Answer: Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, 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: He should buy cotton shirts. This is because cotton has more capacity to hold moisture than synthetic clothes. In summers we have extensive sweating which is easily soaked by cotton shirts and hence, cotton clothes are much better than the clothes made from synthetic material.

Question 10. Give examples to show that plastics are non-corrosive in nature.
?‍♂️Answer: The literal meaning of non-corrosive is resistant to get destroyed by chemical action.

• Following are the examples that show that plastics are non-corrosive in nature.
• Plastic containers do not react with items stored in it.
• They do not get rusted when exposed to moisture and air.
• They do not decompose when left in open for a long period.

Question 11. 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 toothbrush should not be made of the same material. This is because our gums are soft and the bristles should be made of soft material so that it does not harm the gums. On the other hand, the handles should be made up of hard material so that it can give a firm grip.

Question 12. ‘Avoid plastics as far as possible’. Comment on this advice.
?‍♂️Answer: 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. When the plastics are burnt, it releases a lot of poisonous fumes into the atmosphere causing air pollution. These plastic materials when eat up by the animals (like cows), choke their respiratory system.

This can cause death of these animals. The waste plastic articles thrown here and there carelessly get into dirty water drains and sewers, and block them. In a nutshell, plastics can be considered a threat to our environment.

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

?‍♂️Answer:

Question 14. ‘Manufacturing synthetic fibres is actually helping the conservation of forests’. Comment.
?‍♂️Answer: In the manufacturing of synthetic fibres, we use only chemical substances and no natural materials, thus, in turn, we conserve forests.

Question 15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
?‍♂️Answer: Arrange a circuit as shown in the given figure. Leave a gap between two ends of the wire. Place a ther-moplastic in the gap. Observe the bulb.

It is observed that the bulb does not glow. This shows that thermoplastic is a poor conductor of electricity.

Activity 1

Take an iron stand with a clamp. Take a cotton thread of about 60 cm length. Tie it to the clamp so that it hangs freely from it as shown in Fig. 3.3.
?‍♂️Answer:

At the free end suspend a pan so that weight can be placed in it. Add weight one by one till the thread breaks. Note down the total weight required to break the thread. This weight indicates the strength of the fibre. Repeat the same activity with threads of wool, polyester, silk and nylon. Tabulate the data as shown in Table 3.1. Arrange the threads in order of their increasing strength.

• It has a silk-like appearance.
• It is obtained from wood pulp.
• Its fibres can also be woven like those of natural fibres.

?‍♂️Answer: It is obtained from wood pulp.

Synthetic fibres are also called ……….. or ……….
Synthetic fibres are synthesised from raw material called …………
Like synthetic fibres, plastic is also a …………..
?‍♂️Answer: artificial, man-made
mono or petrochemicals
polymers.

Plastics are non-reactive.
Plastics are light and strong.
Plastics are durable.

(i) Saucepan handles
?‍♂️Answer: Saucepan handles are made of thermosetting plastics because they are bad conductors of heat.

(ii) Electric plugs/switches/plug boards.
?‍♂️Answer: Electric plugs/switches/plug boards are made of thermosetting plastics because they are bad conductors of electricity.

• Buckets made of iron get rusted but those made of plastic are not rusted.

• Food can be stored in plastic containers, as they are resistant to chemicals in the food

• Teflon coated pans are used instead of metallic as it doesnot react with chemicals in the food.

It is cheap.
It can be dyed in many colours.
It can be woven like silk.

do not get wrinkled easily
are easy to wash,
easy to maintain.

Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
?‍♂️Answer:

?‍♂️Answer:

• Plastics are non-biodegradable.
• Careless disposal of plastic bags, chokes, drains and blocks the soil.
• If eaten by cows, it can kill them.
• Plastic bags can also contaminate foodstuffs due to poisonous dyes getting absorbed into food.

• for packaging of tablets
• as threads for stitching wounds
• in syringes
• doctor gloves
• for making a number of medical instruments.

• Avoid the use of plastics as far as possible.
• Use bags, made of jute or cloth.
• Biodegradable and non-biodegradable wastes should be separated and disposed off separately.
• Plastics should be recycled and reused.