NCERT Solutions for class 8 Science Synthetic fibres and plastics

Exercise

Q1: Explain why some fibres are called synthetic.

Ans: Some fibres are called synthetic because they are made using chemicals in the lab. Examples: rayon, nylon and polyester.

Q2: Tick the correct answer:

Rayon is different from synthetic fibres because

Ans: (b) it is obtained from wood pulp

Q3: Fill in the blanks with appropriate words

1. Synthetic fibres are also called man-made or human made fibres.
2. Synthetic fibres are synthesized from raw material called petrochemicals.
3. Like synthetic fibres, plastic is also a polymer.

Q4: Give examples, which indicate that nylon fibres are very strong.

Ans: Nylon is used in making ropes, which is used in mountain climbing. It is also used in making car seat belt. These examples shows that nylon fibres are very strong.

Q5: Explain why plastic containers are favored for storing food.

Ans: There are two major reasons for it:

1. Plastic do not react with air or water, hence it does not spoil the food.
2. Plastic containers are easily available at affordable price in the market.

Q6: Explain the difference between thermoplastics and thermosetting plastics.

Ans:

Thermoplastics	Thermosetting plastics
It is easily deformed on heating	It does not deform on heating
It is lightweight	It is strong
It is used for making toys	It is used for making electrical switches
Example: polythene and PVC	Example: melamine and Bakelite

Q7: Explain why the following are made of thermosetting plastics:

1. Saucepan handles
2. Electric plugs/switches/plug board

Ans: (a) Thermosetting plastic is bad conductor of heat. Hence, it is used in making saucepan handles so that we can easily handle the hot saucepan.

            (b) Since, thermosetting plastics are bad conductors of electricity. Hence, they are used in making electrical switches, plugs and plug boards. So, we stay safe from electrical shocks.

Q8: Categories the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’

Ans:

Can be recycled	Cannot be recycled
Plastic toys, carry bags, plastic bowls, plastic covering on electrical wires, plastic chairs	Telephone instruments, cooker handles, ball point pens, electrical switches

Q9: Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Ans: Rana should buy cotton shirt for summer because cotton fabric is better at absorbing sweat. Also, when the air will blow it will make his body cool.

Q10: Give examples to show that plastics are noncorrosive in nature.

Ans: Plastics are noncorrosive in nature because of the following reasons:

1. Plastic do not react with air and water
2. It cannot be easily decomposed by the bacteria

Q11: Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.

Ans: No, handle and bristle should not be made of same material. The bristle should be made of soft material because our gums are very soft and the handle should be made of hard material for better grip.

Q12: ‘Avoid plastics as far as possible’. Comment on this advice.

Ans: Definitely, we should avoid plastics as far as possible because plastics are not environment friendly. It causes soil pollution that reduces the fertility of soil. They do not decompose easily that increase the amount of garbage in our surrounding.

Q13: Match the terms of column A correctly with the phrases given in column B

Ans:

Sr no	Column A	Column B
1	Polyester	Fabrics do not wrinkle easily
2	Teflon	Used to make non-stick cookware
3	Rayon	Prepared by using wood pulp
4	Nylon	Used for making parachutes and stockings

 

Q14: ‘Manufacturing synthetic fibres is actually helping conservation of forests.’ Comment.

Ans: Synthetic fibres are made with the help of chemicals. It reduces our dependency on forests for raw material that conserve the forests.

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