Q. 1. What are synthetic fibres ?
Ans. Fibres made of chemicals by the man are called synthetic fibres.
Q. 2. Name some synthetic fibres.
Ans. Nylon, rayon, acrylic, polyester, etc.
Q. 3. What happens when synthetic fibre is burnt ?
Ans. When burnt, a synthetic fibre starts melting.
Q. 4. Give examples which indicate that nylon fibres are very strong.
Ans. Parachutes and ropes for mountaineering.
Q. 5. 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.
Ans. (b) it is obtained from wood pulp.
Q. 6. Explain the difference between the thermoplastic and thermosetting plastics.
Ans. Following are the differences between thermoplastic and thermosetting plastics :
(1) Thermoplastics can be softened on heating but thermosetting plastics cannot be melted.
(2) Thermoplastics can be bent and thus reshaped again and again but thermosetting plastics cannot be bent.
(3) Thermoplastics are good conductors of heat while thermosetting plastics are bad conductors of heat.
Q. 7. What is cellulose ?
Ans. Cellulose is a polymer made up of a large number of glucose units.
Q. 8. 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|
|Ans.||Column I||Column II|
|(i)||Polyester||(a)||Fabrics do not wrinkle easily|
|(ii)||Teflon||(b)||Used to make non-stick cookwares|
|(iii)||Rayon||(c)||Prepared by using wood pulp|
|(iv)||Nylon||(d)||Used for making parachutes and stockings|
Q. 9. Give examples to show that plastics are noncorrosive in nature ?
Ans. The following examples show that plastics are non-corrosive in nature :
(1) They are used to store chemicals in laboratories as they don’t react with chemicals or other items in the laboratory.
(2) Plastic does not react even with air and water and so it dies not get rusted.
(3) Plastic does not decompose even when left in the open for a long periods.
(4) They are used to store all types of food, as plastic does not react to materials stored in it.
Q. 10. Why are switches and plugs are made of plastics ?
Ans. As plastics are poor conductor of electricity and are also resistant to heat, so they do not allow the electric current to pass through them making them safe to handle. It is due to this that they are used to make electric switches and plugs.
Q. 11. What is PET ?
Ans. PET is a form of polyester and a synthetic material. It is widely used to make films, bottles, utelsils, wires and many other products, the most common and visible usage being PET jars in our kitchens.
Q. 12. Write advantages and disadvantages of synthetic fabrics.
Ans. Advantages :
(1) Synthetic fibres are strong so they can take up heavy loads easily.
(2) They have got high tensile strength, which enables them to carry weights.
(3) They easily retain their original shape, even if they get wrinkled. So they are convenient to wash and wear.
(4) They have great elasticity due to which can be easily streched.
(5) Synthetic fibres are generally soft, so they are used to make variety of clothes and clothing materials.
(1) Synthetic fibres cannot absorb moisture. This makes them unsuitable to be warm during summers. When our body sweats. This make body sticky and irritates the skin.
(2) They are dangerous to be worn near fire or heat, as they easily catch fire and is unfit to be worm.
(3) They cannot be easily ironed as they melt very easily.
Q. 13. Fill in the blanks :
(1) ............... is used as a coating on the surface of non-sticking frying pans.
(2) The simplest molecule of a polymer is called ............... .
(3) When a ............... fibre is burnt, the residue swells up to form black ash.
(4) A nylon wire is ............... than steel wire.
(5) Plastics are ............... conductors of electricity.
Ans. (1) Teflon is used as a coating on the surface of non-sticking frying pans.
(2) The simplest molecule of a polymer is called monomer.
(3) When a silk fibre is burnt, the residue swells up to form black ash.
(4) A nylon wire is stronger than steel wire.
(5) Plastics are poor conductors of electricity.
Q. 14. Write a note on nylon and its uses.
Ans. Nylon is a man-made fibre. It was made first in 1931 without using any natural raw material, i.e., material from plants or animals. It was prepared from coal, water and air. It was the first fully synthetic fibre.
Nylon fibre is strong, elastic and light. It lustrous and easy to wash. So, it has become very popular for making clothes.
Apart from clothes, many articles are made from nylon, such as socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains, etc. Nylon is also used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.
Q. 15. What are biodegradable and non-biodegradable materials ?
Ans. A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable while a material which is not easily decomposed by natural processes is termed non-biodegradable.
Q. 16. Is plastic environment friendly ? Why ?
Ans. As plastic takes several years to decompose, it is not environment friendly. The burning process in the synthetic material is very slow and it does not get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution. So its use should be avoided.