Class-8 SCIENCE CHAPTER-3 SYNTHETIC FIBRES AND PLASTICS

 EVENTS CONVENT HIGH SCHOOL

15/01/2021                         CLASS-8                                  SLOT-2

  SCIENCE

CHAPTER -3 SYNTHETIC FIBRES AND PLASTICS

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Question 1.Explain why some fibres are called synthetic.
Answer:All fibres are not natural. Some fibres are man-made. The fibres made artificially are called synthetic fibres.

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

Answer:(a) artificial, man-made
(b) petrochemicals
(c) polymer

Question 4.Give examples which indicate that nylon fibres are very strong.
Answer:Nylon fibres are used to make ropes for rock climbing and for parachutes.

Question 5.Explain why plastic containers are favoured for storing food.
Answer:The main advantages of using plastic containers for storing food are:

    (a)  plastic has light weight.

    (b)  lower price 

    (c)  good strength and

    (d)  are easy to handle.

 

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

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

(a) Saucepan handles
(b) Electric plugs/switches/plug boards.

Answer:(a) Thermosetting plastic does not soften on heating. Also it is a bad conductor of heat. This is why saucepan handles are made of bakelite which is a thermosetting plastic.

(b) Thermosetting plastic cannot be softened on heating. It is a bad conductor of heat as well as electricity. This is why electric plugs/switches/plug boards are made of backelite which is a thermosetting plastics.

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, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Answer:Materials can be recycled: Telephone instruments, plastic toys, ball point pens, plastic bowls. (As these are thermoplastics, so these can be recycled).
Materials cannot be recycled: Cooker handles, carry bags, plastics, covering; on electric wire, plastic chairs, etc. (As these are thermosetting, so cannot be recycled.)

Question 9.Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, a giving your reason.

Answer:I will advise Rana to wear cotton clothes. Synthetic fibres do not absorb water or sweat. They stick to the body in summer and do not allow ventilation of air. Thus, they made us uncomfortable during summer. Cotton clothes which are natural fabric, do not contain heat, instead they reflect out heat. Besides, they also provide aeration. So, during summer, we prefer cotton clothes and not the synthetic clothes.

Question 10.Give examples to show that plastics are noncorrosive in nature.
Answer:The plastics are non-corrosive, that is, they do not react or do not have chemical reaction with the materials contained in it. That is why containers like bucket, mug, water bottles and food containers are made up of plastics.

Question 11.Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Answer:Handle and bristles of a tooth brush should be made of different materials because they have different uses and require different properties in the material, for example, bristles should be much more flexible than the handle.

Question 12.Avoid plastics as far as possible’. Comment on this advice.
Answer:Plastic takes several years to decompose. So it is not environment friendly. Burning of plastic releases lots of poisonous gases which cause pollution to the atmosphere. The burning process of plastics is quite slow and it is not burnt completely. Therefore, use of plastics should be avoided as far as possible.

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

Answer:

A	B
(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