NCERT 8th Class (CBSE) Science: Synthetic Fibres and Plastics

Question: Give two examples each of natural and synthetic fibres.

Answer: Natural fibres: Cotton, Silk

Synthetic fibres: Rayon, Nylon

Question: What is a polymer?

Answer: Synthetic fibres are made up of molecules called polymers. Polymers are huge molecules-usually consisting of long chains made from thousand of similar small molecules called monomers.

Question: Why is rayon called regenerated fibre?

Answer: Rayon is called a regenerated fibre because the original raw material, cellulose is broken down and then reformed. This makes it strong and easier to dye in a variety of colours.

Question: List two disadvantages of synthetic fibres?

Answer: Two disadvantages are:

1. In hot and humid weather, these clothes stick to the body and make us feel uncomfortable.
2. Synthetic fibres catch fire very readily. They are easily inflammable. They melt on heating and stick to the body of the person wearing them, causing severe burn.

Question: What is plastic? All plastics have the common property-what is it?

Answer: Plastic is a material that can be moulded or formed into different shapes. All these materials have one co common property – they are made of polymers.

Question: Why are plastic bottles commonly used to store chemicals in a chemistry laboratory?

Answer: Plastics have no reaction with water and air. They are non-reactive and do not corrode easily. That is why they are used to stored chemicals and other materials.

Question: List the important properties of nylon that makes it a useful synthetic fiber. Give important uses of nylon.

Answer: Important properties of nylon:

1. It is very strong and elastic, infact, nylon thread is stronger than steel wire.
2. It is light and wrinkle-resistant.
3. It is wear resistant, that is why nylon garment lasts for a long time.
4. It is easy to wash and absorbs very little water, therefore, garments made from nylon dry quickly.
5. It is lustrous in appearance.

Important uses of nylon:

1. Garments such as saris are made from nylon. Since it is wear resistant, garments made from it last for long time.
2. Being very strong, nylon fibre is used to make ropes (including ropes used during rock-climbing), tents, fishing nets and parachutes.
3. It has good elasticity and is, therefore, useful for making socks and stockings.
4. Nylon is also used to make toothbrushes, combs, zip fasteners and machine parts.