NCERT Solutions For Class 8 Science Chapter 3 Synthetic Fibres and Plastics

Plastics are non-reactive and noncorrosive in nature. They are not corroded even by strong chemicals. That is why various kind of chemicals are stored in plastics bottles.

                  A                                     B

1. Polyester           (d) Fabrics do not wrinkle easily
2. Teflon               (c) Used to make non-stick
3. Rayon               (a) Prepared by using wood pulp
4. Nylon                (b) Used for making parachutes and stockings

Handle and bristle of a tooth brush should not be made of the same material. This is because handle of brush is strong and hard, while bristles are soft and flexible.

1. Saucepan handles are made of thermosetting plastics because these plastics do not soften on heating.
2. Thermosetting plastics are poor conductors of heat and electricity. Therefore, they are used in making electric plugs, switches, plug boards, etc.

The plastic containers are favoured for storing food because plastic is non-reactive, corrosion resistant, cheap, durable, strong and light in weight.

Nylon fibres are strong, elastic and light. In fact they are stronger than steel wire. They are used in making ropes for rock climbing and parachutes. This usage indicates that nylon fibres are very strong.

Man-made fibres are called synthetic fibres. These fibres are prepared from petrochemicals with the help of various processes. Examples of some synthetic fibres are nylon, rayon, polyester, acrylic, etc.

Raw material used for making natural fibres is mainly derived from plants. It requires cutting of lots of trees leading to deforestation. On the other hand raw materials required for synthetic fibres are mainly obtained from petrochemicals. It means for manufacturing of synthetic fibres, cutting of trees is not needed. Hence, it can be said that ‘manufacturing synthetic fibres is actually helping in conservation of forest’.

Plastics are non-biodegradable, i.e. they are not decomposed by micro-organisms. Once introduced into the environment they may take several years to decompose. Plastics when burnt produce poisonous gases. They are dangerous to animals like cows, which swallow these bags from garbage. These bags choke the respiratory system of the animals or form a lining in their stomach and may cause their death. Hence, we should avoid plastics as far as possible.

1. artificial,  man-made
2. petrochemicals
3. polymer

Rayon is different from synthetic fibres because

1. it has a silk-like appearance.
2. it is obtained from wood pulp. (✓)
3. its fibres can also be woven like those of natural fibres.

We can set two circuits to show that thermoplastic is a poor conductor of electricity. For this we need two bulbs, wires, two batteries, a piece of metal and a pipe made of thermoplastic.

Set up the circuits with metal and plastic pipe separately as shown below.

When you turn the switch on the current flows and the bulb glows in the first circuit (circuit with metal) while, bulb does not glow in the second circuit (circuit with plastic).

This activity confirms that thermoplastic is a poor conductor of electricity.