Question: 1. Explain why some fibres are called synthetic.
Answer: Some fibres are called as synthetic fibres because these are not obtained naturally, but are man-made fibres manufactured by using chemicals. These comprise of small units joined together to form long chains. Examples are PVC, rayon, Dacron, polyester etc.
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 __________
Answers:
(a) Synthetic fibres are also called artificial or manmade fibres.
(b) Synthetic fibres are synthesised from raw materials called petrochemicals.
(c) Like synthetic fibres, plastic is also a polymer.
Question: 4. Give examples which indicate that nylon fibres are very strong.
Answer:
- Nylon fibres are very strong, therefore used in making Parachutes and ropes for rock climbing.
- Nylon is used in making tyre cords, fishing nets and seat belts.
Question: 5. Explain why plastic containers are favoured for storing food.
Answer:
Plastic containers are favoured for storing food because plastic is non-reactive, therefore will not react with the ingredients of the food items.
Question: 6. Explain the difference between thermoplastic and thermosetting plastics.
Answer:
The difference between thermosetting plastics and thermoplastics are
| Thermoplastics | Thermosetting plastics |
| These are can be remoulded easily on heating. | These cannot be remoulded on heat. |
| These can be easily bent. | These cannot be bent easily, rather they break on applying force. |
| Examples: Polyethene, PVC etc | Examples: Bakelite, Epoxy resin |
Question: 7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Answer:
- a) Thermosetting plastics are used to make saucepan handles because they are bad conductors of heat and these plastics do not soften on heating,
- b) Bakelite is a bad conductor of heat and electricity. This is why it is used for making electric plugs, switches, plug boards, etc.
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, ballpoint pens, bowls, plastic covering on electrical wires, plastic chairs, and electrical switches.
| Can be recycled | Cannot be recycled |
| carry bags | cooker handles |
| plastic covering on electrical wires | electrical switches |
| plastic chairs | Telephone instruments |
| plastic toys | |
| ballpoint pens |
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 a cotton shirt for the summer because cotton is a good absorber of water. Pores in the cotton fabric help in evaporating sweat and keep our body cool.
Question: 10. Give examples to show that plastics are non-corrosive in nature.
Answer: Plastics are non-corrosive in nature, they do not react with air and water. Plastics do not react even with strong chemicals. For example, the cleaning chemicals like acids and detergents are stored in plastic bottles and not in metal containers.
Question: 11. Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.
Answer:
The handle of the toothbrush should be hard and strong so that it has a firm grip while the bristle should be soft and flexible so that it should not harm gums. Bristles are made of nylon fibres and the handle is made of hard plastic.
Question:12. ‘Avoid plastics as far as possible. Comment on this advice.
Answer:
We should avoid plastics as far as possible because:
- plastics are non-biodegradable in nature and take several years to decompose.
- If burnt they release poisonous gases resulting in pollution.
- Cows and other animals swallow plastic bags thrown in the garbage which chokes their respiratory system and even causes death.
Question: 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 cookwares
(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
Question:14. ‘Manufacturing synthetic fibres is actually helping conservation of forests. Comment.
Answer:
The manufacturing of synthetic fibres is helpful in the conservation of forests because if we use natural fibres, the raw materials for them have to be derived from the plants, which requires cutting off lots of trees. This results in deforestation. Thus, this proves to be helpful in the conservation of forests.
Question:15. Describe an activity to show that thermoplastic is a poor conductor of electricity
Answer:
In order to show that thermoplastic is a poor conductor of electricity, we will perform an activity.
Things required: a bulb, wires, a battery, a piece of metal and a plastic pipe. After setting the experiment switch on the current, you will observe that the bulb glows in figure 1. But, the bulb does not glow in figure 2. Hence a plastic pipe (which is a thermoplastic) is proved to be a poor conductor of electricity.