SCIENCE CLASS 8

SYNTHETIC FIBRES AND PLASTICS

EXERCISES

Question number 1

Explain why some fibres are called synthetic.

Answer number 1

Some fibres are called synthetic fibres because these are man made fibres prepared by using chemical substances. Synthetic fibres are nylon, rayon, acrylic, polyester etc.

Question number 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 number 2

(b) it is obtained from wood pulp.

Question number 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 __________ .

Answer number  3

(a) artificial, manmade
(b) petrochemicals
(c) polymer

Question number 4

Give examples which indicate that nylon fibres are very strong.

Answer number 4

1. Parachutes and ropes of rock climbing are made of nylon because of its strongness.
2. Nylon is used in making accessories like rackets.
3.Nylon is used in making scat belt, fishing nets and tyre card.

Question number 5

Explain why plastic containers are favoured for storing food.

Answer number 5

Plastic containers  are used for storing food because it is non - reactive and does not react with the ingredients of food items.

Question number 6

Explain the difference between the thermoplastic and thermosetting plastics.

Answer number  6

Thermosetting plastic

1.Thermosetting plastic cannot be bent.
2.On heating thermosetting plastic, it cannot be softened. because of this it cannot be reshaped.

Thermoplastic

1.Thermoplastic can be bent easily.
2.On heating the thermoplastic, it become softened and can be molded and reshaped easily.

Question number 7

Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards

Answer number 7

(a) Thermosetting plastic are bad conductor of heat because of having these property saucepan handles are made of thermosetting plastic and on heating these plastic do not get softened.

(b) Thermosetting plastic are bad conductor of heat and electricity. Because of having these property it is used for making electric plugs, switches, plugs boards etc.

Question number 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 and electrical switches.

Answer number 8

Can be recycled          Cannot be recycled
1.Plastic chair             1.Cooker handles
2.Plastic bowl             2.Electrical switches
3.Plastic toys               3.Telephone
4.The plastic covering
on electrical wires
5.Carry bags
6.Ballpoint pens

Question number 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 number 9

Rana should buy a cotton shirt for the summer because cotton is a good absorber of water so it can soak the sweat coming out of the body and expose it to the environment and it evaporate. Thus it helps in cooling our body. Synthetic materials are not having this property.

Question number 10

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

Answer number 10

Plastic do not reacts with water, air. They are not corroded easily even if they come in contact with strong chemicals. For example, the cleaning chemical are stored in plastic bottles, instead of the metal container.

Question number 11

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

Answer number 11

The handle and bristles of a toothbrush should not be made of the same material as the handle of the toothbrush should be strong to hold. The bristles should be soft and flexible because its gives friction to gum while cleaning the teeth.

Question number 12

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

Answer number 12

We should avoid plastics as far as possible because plastic are non biodegradable in nature. Once comes into the environment they cause pollution. They can't be destroyed and remains in nature forever. If burnt they release poisonous gases.
 Because of the demerits of plastic, it should be avoid as far as possible.

Question number 13

Match the terms of column I correctly with the phrases given in column II.
Column I                 Column II
(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 number 13

Match the terms of column I correctly with the phrases given in column II.
Column I                Column II
(i) Polyester      (d) Fabrics do not wrinkle
                            easily
(ii) Teflon          (c) Used to make non-stick
                            cookwares
(iii) Rayon         (a) Prepared by using
                            wood pulp
(iv) Nylon          (b) Used for making
                            parachutes and stockings

Question number 14

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

Answer number 14

The manufacturing of synthetic fibres is helpful in the conservation of forests because for natural fibres raw material is obtained from the plants which required cutting of lots of trees. Hence manufacturing of synthetic fibres helpful in the conservation of forests.

Question number 15

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

Answer number 15

In order to prove that thermoplastic is a poor conductors of electricity the under mention experiment is to be done. For the experiment one piece of plastic material is to be taken and its both end should be connected to a battery and bulb per the diagram. When current pass through the circuit the bulb does not glow it prove that thermoplastic are poor conductor of electricity.

ALSO SEE SOLUTIONS OF FOLLOWING CHAPTERS :

Crop Production And Management
Microorganisms - Friend And Foe
Synthetic Fibre And Plastic

Material : Metals And Non - Metals

Coal And Petroleum