NCERT Solutions for Class 8 Science Chapter 3

NCERT Solutions for Class 8 Science Chapter 3 Synthetic Fibres and Plastics is given below. Video Format solutions of all chapters class 8 science are also available. Download 8 Science App for offline use.

Important Terms on Class 8 Science Chapter 3

1. What are synthetic fibres?

In this part of the content focuses on the importance of synthetic fibre, uses with their origin, which is related to the Textile Industries. As you know, the clothes which we wear are made of fabrics. Fab is made from natural or artificial sources. Cotton, silk, wool is an example of natural fibre. Nylon, rayon is the example of synthetic fibre. But why it is so? The fibres which are made in the laboratory by human beings from a chemical substance called synthetic fibre. That is why these are called ‘Synthetic’ or ‘Man-made’ fibres. Generally, synthetic refers artificial or which are not natural.

2. Monomer and Polymer

In the laboratory with the help of chemical substances, many small units are made, called a monomer. For getting synthetic fibre, many such small units combined to form a single large unit called as polymer. You are surprised to know that polymers occur in nature also. Such as cotton, it is a polymer of cellulose and that cellulose is made up of glucose.

3. Rayon – A Types of Synthetic Fibres

Chapter 3 of Class 8 Science deals with different types of synthetic fibres with their importance in our daily life. We know that we get silk from the silkworm. But we wear many dresses which are not made from silk, but they appear to resemble silk. Towards the end of the 19th century, scientists were successful in obtaining a fibre having properties similar to that of silk. We use the chemical treatment of the wood pulp to get these fibres. This fibre is known as ‘Artificial Silk’ or ‘Rayon’. Rayon is mixed with cotton to make bed sheets or mixed with old to make carpets.

4. Nylon – A Types of Synthetic Fibres

Nylon is another man-made fibre. It was prepared from coal, water and air. It was the first fully synthetic fibre. Nylon fibre was strong, elastic and light. We use many articles made from nylon, such as socks. Ropes, tents, parachutes, toothbrushes, curtains etc.

5. Polyester and Acrylic

Polyester is another synthetic fibre. Polyester is made up of the repeating units of a chemical called ‘Easter’. Terylene and PET are a very popular form of polyester. Remember, polycot is a mixture of polyester and cotton. Polywool is a mixture of polyester and wool. Fabric made from these fibres does not get wrinkle quickly. They remain crisp and easy to wash. Acrylic is another type of synthetic fibre which appear to resemble like wool.

6. Characteristics of Synthetic Fibres

Class 8 Science Chapter 3 focuses on the characteristics of synthetic fibres which helps us to understand that either we should use the synthetic fabric or not. Do you know how do we get synthetic fibres? Remember, all the synthetic fibres are prepared by many processes using raw materials of petroleum origin, called ‘Petrochemicals’. Synthetic fibres process is unique characteristics which make them popular dress materials. As they are dry up quickly, durable, less expensive, readily available and easy to maintain. You must have noticed that synthetic fibres melt on heating. This is a disadvantage of synthetic fibres. If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of a person wearing it. We should, therefore, not wear synthetic clothes while working in the kitchen or in a laboratory.

7. Plastic in Day to Day Life

Plastics are extensively used in our everyday life – wherever you look, and you will probably find something made of plastic. The list is endless if we start counting articles like toothbrush, comb, toys, bottle, carry bags, furniture, and so many other things. Remember, plastic is also a polymer like synthetic fibre. Plastic articles are available in all possible shapes and sizes. Moreover, plastic can be recycled, reused, coloured, melted or made into wires. That is why we find it as a variety of uses. But some plastic which gets deformed easily on heating and can be made easily known as ‘Thermoplastic’. Such as polythene. Furthermore, there some plastic which when moulded once, it cannot be softened and by heating, called ‘Thermosetting’ plastic. Such as Bakelite and Melamine. Bakelite is a poor conductor of heat and electricity whereas melamine is a versatile material, it resists fire and can tolerate heat better than other plastics.

8. Plastic as Materials of Choice

Today if we think to store a food item, water, milk, pickles, dry food etc., plastic containers seem most convenient. This is because of their lightweight, lower price, good strength and easy handling.
You know that metals like Iron get rusted when left exposed to moisture and air. But plastic does not react with water and air easily. Since plastic is very light, strong, durable and can be moulded into different shapes and sizes, it is used for various purposes. And also plastic is generally cheaper than metals. As you know that, plastic is a poor conductor of heat and electricity. That is why electrical wires have plastic covering, handles of screwdrivers and frying pans are made of plastic. Plastics find extensive use in many industries, such as the health care industry, fire industry, IT industry, wrapping industry, and so on.

9. Plastic and the Environment

Do you know, around the world, one million plastic drinking bottles are purchased every minute, while up to 5 trillion single-use plastic bags are used worldwide every year? In total, half of all plastic produced is designed to be used only once — and then thrown away. Ultimately plastic finds its way in the garbage. Disposal of plastic is a major problem. But why? A natural process does not easily decompose plastic, so it is termed as non-biodegradable. While those materials which get decomposed through the natural process, such as action by bacteria, called biodegradable.

10. Plastic as a Non-Biodegradable

Since plastic takes several years to decompose, besides, the burning process of plastic, it releases lots of poisonous fumes in the atmosphere. Hence, it is not environment friendly. Now, we are producing about 300 million tonnes of plastic waste every year, that’s nearly equivalent to the weight of the entire human population. You can see the impact of plastic on weather, atmosphere, life on aquatic and terrestrial organisms, including human beings. So, it is better to recycle plastic waste or avoid the use of plastic as far as possible.

Class 8 Science Chapter 3 MCQ with Answers

1. Pick the synthetic fibre out of the following?
(a) Cotton
(b) Nylon
(c) Jute
(d) Wool
2. Which of the following groups contain all synthetic substances?
(a) Nylon, Terylene, Wool
(b) Cotton, Polycot, Rayon
(c) PVC, Polythene, Bakelite
(d) Acrylic, Silk, Wool
3. Which is a thermosetting plastic?
(a) Melamine
(b) Polythene
(c) PVC
(d) Nylon
4. The most suitable material for the preparation of handles of cooking utensils is
(a) Polythene
(b) PVC
(c) Nylon
(d) Bakelite
5. The material similar to silk in appearance is
(a) Nylon
(b) Rayon
(c) Polyester
(d) Terylene
6. Which of the following is not a common property of plastics?
(a) Non-reactive
(b) Light in weight
(c) Durable
7 Good conductor of electricity
10. The material which is commonly used for making kitchen containers is
(a) PVC
(b) Acrylic
(c) Teflon
(d) PET
8. Polycot is obtained by mixing
(a) nylon and wool
(b) polyester and wool
(c) nylon and cotton
(d) polyester and cotton
9. Fill in the blanks.
(i) A polymer is a chain of many small units joined together which are called ______.
(ii) The synthetic fibres are also known as ______ fibres.
(iii) The first fully synthetic fibre was ______.
(iv) A fibre similar to wool is ______.
(v) A plastic used for making crockery is ______.
10. Plastic is used for making a large variety of articles of daily use and these articles are very attractive. But it is advised to avoid the use of plastic as far as possible. Why?
11. PVC (polyvinyl chloride) is a thermoplastic and is used for making toys, chappals, etc. Bakelite is a thermosetting plastic and is used for making electrical switches, handles of various utensils, etc. Can you write the major difference between these two types of plastics?

1 (b)
2 (c)
3 (a)
4 (d)
5 (b)
6 (d)
7 (d)
8 (d)
9 (i) monomers (ii) man-made (iii) nylon (iv) acrylic (v) melamine
10 Due to its non-biodegradable nature it causes environmental pollution.
11 Thermoplastics get deformed easily on heating and can be bent easily on heating. On the other hand thermosetting plastics when molded once cannot be softened on heating.

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