NCERT Solutions For Class 8 Science Chapter – 3 Synthetic Fibers and Plastics
Q1. Explain why some fibers are called synthetic.
Answer:-
Some fibers are called as synthetic fibers because these are manmade fibers prepared by using chemicals. These are made of small units that join together to form long chains. Some of the examples of synthetic fibers are nylon, rayon acrylic, polyester etc.
Q2. Mark the correct answer.
Rayon is different from synthetic fibers because
- it has a silk -like appearance.
- it is obtained from wood pulp.
- It is fibers can also be woven like those of naturals fibers.
Answer:-
It is obtained from wood pulp.
Q3. Fill in the blanks with appropriate words.
- Synthetic fibers are also called ______ or ______ fibers.
- Synthetic fibers are synthesised from raw materials called ______.
- Like synthetic fibers, plastic is also a _______.
Answer:-
- Synthetic fibers are also called artificial or manmade fibers.
- Synthetic fibers are synthesised from raw material called petrochemicals.
- Like synthetic fibers, plastic is also a polymer.
Q4. Give examples which indicate that nylon fibers are very strong.
Answer:-
Following are the examples that indicates nylon fibers are very strong.
- Parachutes and ropes of rock climbing are made of nylon
- Nylon is used in making sports accessories like rackets.
- Nylon is used in making sport accessories like rackets.
Q5. Explain why plastics containers are favored for strong food.
Answer:-
Because plastic is non – reactive and will not react with the ingredients of the food items.
Q6. Explain the difference between thermoplastic and thermosetting plastics.
Answers:-
The= difference between the thermosetting plastics and thermoplastics are
| Thermosetting Plastics | Thermoplastic |
| Cannot be bent, it will break if we attempt to bend thermo setting plastic | Thermoplastics can be bent easily. |
| On heating thermosetting plastics , it cannot be softened. This is the reason cannot be reshaped once it is molded. | On heating the thermoplastics , it becomes softened and can be molded and reshaped easily.
|
Q7. Explain why the following are made of thermosetting plastics.
- Saucepan handles
- Electric plugs/switches/plug boards
Answer:-
- Thermosetting plastics are used to make saucepan handles because they are bad conductors of heat and also on heating these plastics do not get softened.
- Bakelite is a kind of thermosetting plastic which is a bad conductor of heat and electricity. Because of this property it is used for making electric plugs switches , plug boards, etc.
Q8. Categorise the materials of the following products into ‘can be recycled and cannot be recycled’.
Telephone , instruments , plastics toys , cooker handles, carry bags , ball point pens , plastics bowls , plastics covering on electrical wires, plastic chairs, electrical switches.
Answer:-
| Can be recycled | Cannot be recycled |
| Plastics chair | Cooker handles |
| Plastics bowls | Electrical switches |
| Plastics toys | Telephone |
| The plastics covering on electrical wires | |
| Carry bags | |
| Ballpoint pens |
Q9. 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 and not a synthetic shirt. Cotton is a good absorber of water. So it can soak the sweat coming out of the body and expose it to the environment. Thus, it helps in evaporating the sweat and helps in cooling our body.
Q10. Give examples to show that plastics are noncorrosive in nature.
Answer:-
Plastics are non – corrosive in nature, they donot react even if they come in contact with strong chemicals. For example, the cleaning chemicals that we use at home are stored in plastics bottles, instead of metal containers.
Q11. Should the handle and bristles of a both brush be made of the same materials? Explain your answer
Answer:-
The handle and bristle of a toothbrush should not be made of the same material as the handle of the toothbrush should be hard and strong while the bristle should be soft and flexible.
Q12. ‘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. Once introduced into the environment they cause pollution. If burnt they releases poisonous gases and the plastics bags thrown in the garbage dumb are swallowed by animals choke their respiratory systems and causes fatalities in animals.
Q13. 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 stocking |
| (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 cookwares |
| (iii) Rayon | ( a ) Prepared by using wood pulp |
| (iv) Nylon | ( b) Used fr making parachutes and stocking |
Q14. ‘Manufacturing’ synthetic fibers is actually helping conservation of forests’ Comment.
Answer:-
The manufacturing of synthetic fiber is helpful in the conservation of forests because if we use natural fibers, the raw materials for them have to be derived from the plants, which require cutting off lots of tree. This proves to be helpful in conservation of forests.
Q15. Describe an activity to show that thermoplastics is a poor conductor of electricity
Answer:-
In order to show that thermoplastics is a poor conductor of electricity we will design a circuit. For that, we need a bulb some wires , a battery , a piece of metal and a plastics pipe (as shown in the figure below.) After setting the experiments switch on the current , you will observe that the bulb grows in the former case. In the letter case, the bulb does not glow Hence a plastics ( which is a thermoplastics) is shown to be a poor conductor of electricity.
