8th std science synthetic fibers and plastics 2020-21

Information's | Sunday, 2 May 2021


1.   Explain why some fibres are called synthetic.

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.

3.   Fill in the blanks in the following statements.

(a) Synthetic fibres are also called            or          fibres.

(b) Synthetic fibres are synthesised from raw materials calle

(c) Like synthetic fibres, plastic is also a              .

4.   Give examples which indicate that nylon fibres are very strong.

5.   Explain why plastic containers are favoured for storing food.

6. Explain the difference between thermoplastic and thermosetting plastics.

7. Explain why the following are made of thermosetting plastics. (a)  Saucepan handles

(b)  Electric plugs/switches/plug boards


8. Categorize 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.

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

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

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

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

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

A B

(i) (ii) (iii)

(iv)

Polyester Teflon Rayon

Nylon

(a) (b) (c)

(d) Prepared by using wood pulp

Used for making parachutes and stockings

Used to make non-stick cookware

Fabrics do not wrinkle easil

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

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

1. Fibres that are prepared by man using chemicals are known as synthetic fibres. Synthetic fibres are also known as manmade fibres.

2.     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.

3.

(a)  Synthetic fibres are also called  artificial or  man-made

fibres.

(b)  Synthetic fibres are synthesised from raw materials called

petrochemicals.

(c)  Like synthetic fibres, plastic is also a  polymer.

4. Nylon fibres are used for making ropes for climbing rocks and for making parachutes. This example indicate that nylon fibres are very strong.

5. The Plastic containers are favoured for storing food because of their characteristics like light weight, Lower price, Good strength, Easy handling.

6.     There  are  two  types  of  plastics:  Thermosetting  plastics  and

Thermoplastics. 

Thermosetting plastic

Thermoplastic

Thermosetting plastic cannot be bent easily. It may break when forced to bend.

Thermoplastic can be bent easily.

Thermosetting plastic cannot be softened by heating. Thus, it cannot be reshaped once molded.

Thermoplastic can be softened easily by heating. Thus, it can be reshaped.

7.

(a)  Saucepan handles are made of thermosetting plastics because these plastics are not softened on heating.

(b)   Bakelite is a thermosetting polymer which is bad conductor of heat and electricity used for making electric plugs, switches, plug boards, etc.

8

Cannot  be recycled

Can be recycled

Telephone instruments

Plastic toys

Cooker handles

Plastic chairs

Electrical switches

Carry bags

Plastic covering on electrical wires

Plastic bowls

9. Rana  should  buy  a  cotton  shirt  because  cotton  is  a  good absorber of sweat. It can soak the sweat coming out of our body and expose it to the environment. Thus, it helps in evaporating the sweat and cooling our body.

10. Plastics are non-corrosive in nature. In our day today life we use plastics to store many detergents and house cleaning chemicals. Where plastic is not effected by chemicals.

11. No. The handle and bristles of toothbrush be made from different chemicals because we need a soft material in making bristles to brush our teeth. Whereas handle is made from a strong plastic.

12. Plastics   are   non-biodegradable   once   introduced   into   the environment takes years in decomposition. On burning releases poisonous gases which are harmful to the living beings. The plastics even choke the respiratory tract of animals when consumed leading to death. Therefore, usage of plastic should be avoided.


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