NCERT Class 8 Science Solutions Chapter 3 Synthetic Fibres and Plastics

NCERT Class 8 Science Solutions Chapter 3 Synthetic Fibres and Plastics

Question-1

Explain the reason why some of the fibres are called synthetic.

Answer-

The reasons why some of the fibres are called synthetic is because man has prepared them by using chemicals. These are made of small units that join together to form long chains. Some of the examples of synthetic fibres are nylon, rayon, acrylic, polyester etc.

Question-2

Why is rayon different from synthetic fibres?

Answer-

Rayon is different from synthetic fibres because it is obtained from wood pulp.

Question-3

Fill in the blanks with the correct words:

1. a) _____and_______ fibres are also called synthetic fibres.
2. b) Synthetic fibres are synthesized from raw materials called________.
3. c) Like synthetic fibre, plastic is also a _______.

Answers-

a)Artificial and man-made fibres are also called synthetic fibres.

1. b) Synthetic fibres are synthesized from raw materials called petrochemicals.
2. c) Like synthetic fibres, plastic is also called a polymer.

Question-4

List out a few examples that prove that nylon fibres are very strong.

Answer-

Nylon fibres are very strong as it is used for making ropes used for climbing rocks and for making parachutes. This shows the strength of the nylon fibre.

Question-5

Why do you think only plastic containers are mostly favoured for storing eatables?

Answer-

Here are some of the reasons that are responsible for the plastic container being favoured for storing food

1. a) good strength
2. b) lightweight
3. c) Cheap price
4. d) easy to handle

Question-6

Differentiate between thermosetting plastics and thermoplastics.

Answer-

The difference between the thermosetting plastics and thermoplastics are

Thermosetting plastic	Thermoplastic
Thermosetting plastic cannot be easily bent but if we force to bend, it will break.	We can bend thermoplastics easily.
On heating thermosetting plastics, it cannot be softened. This is the reason it cannot be reshaped once it is molded.	On heating the thermoplastics, it becomes softened and can be molded and reshaped easily.

Question-7

Why the following are made of thermosetting plastics? Explain.

1. i) Electric plugs/switches/plugboard
2. ii) Saucepan handles

Answer-

1. i) Bakelite is a kind of thermosetting plastic and is a bad conductor of heat and electricity. That is why it is used for making electric plugs, switches, plugboards, etc.
2. b) Thermosetting plastics are used to make saucepan handles because, on heating, these plastics do not get softened and also it is a bad conductor of heat and electricity.

Question-8

Classify the following products as to which can be recycled and which cannot be.

Plastic chairs, plastic bowls, plastic covering on electrical wires, plastic toys, carry bags, electrical switches, cooker handle, ballpoint pens and telephone instruments.

Answer-

Can be Recycled	Cannot be recycled
Plastic chairs	Cooker handles
Plastic bowls	Electrical switches
Plastic toys	telephone
The plastic covering on electrical wires
Carry bags
Ballpoint pens

Question-9

By giving a reason, suggest Mahesh as to why he should buy a cotton shirt for summer and not a synthetic shirt.

Answer-

Mahesh should buy a cotton shirt for the summer and not a synthetic shirt because 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.

Question-10

Give a reason as to why plastics are non-corrosive in nature with an example.

Answer-

Plastics are non-corrosive in nature even if they come in contact with strong chemicals which is because of their non-reactive nature with most of the materials. For example, the cleaning chemicals that we use at home are stored in plastic bottles, instead of metal containers.

Question-11

Explain why the handle and bristle of a toothbrush should not be made of the same material.

Answer-

The handle and bristle of a toothbrush 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.

Question-12

Why should we avoid plastics as far as possible?

Answer-

We should avoid plastics as far as possible because plastics are non-biodegradable in nature. Once introduced into the environment, it takes several years to decompose. They pollute the environment. We cannot burn them as well because if burnt, it releases poisonous gases. Likewise, the plastic bags thrown in the garbage dumb are swallowed by animals like cows, which choke their respiratory system and can even prove fatal. Therefore, we should avoid plastics as far as possible.

Question-13

Match the terms of side A correctly with the phrases given inside B.

A	B
i) Teflon	a) used for making parachutes and stockings
ii) Nylon	b)fabrics do not wrinkle easily
iii) Polyester	c) prepared by using wood pulp
iv) Rayon	d) Used to make non-stick cookware.

Answer-

A	B
i) Teflon	d) Used to make non-stick cookware.
ii) Nylon	a) Used for making parachutes and stockings
iii) Polyester	b) fabrics do not wrinkle easily
iv) Rayon	c) prepared by using wood pulp

Question-14

Why do you think is the manufacturing of synthetic fibre helpful in the conservation of the forest?

Answer-

The manufacturing of synthetic fibres is helpful in the conservation of forests because if we use natural fibres, the raw materials for them have to be derived from the plants, which means cutting off lots of trees. This leads to deforestation. But raw materials of synthetic fibres are mainly petrochemicals. Hence this proves to be helpful in the conservation of forests.

Question-15

Show and describe an activity to prove that thermoplastic is a poor conductor of electricity.

Answer-

In order to show that thermoplastic 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 plastic pipe (as shown in the figure below). After you switch on the current, you will observe that the bulb glows in the former case. In the latter case, the bulb does not glow. Hence a plastic pipe (which is a thermoplastic) is shown to be a poor conductor of electricity.