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 Important Questions For Practice
Give Examples To Show That Plastics Are Noncorrosive In Nature.
We can store various kinds of chemicals and other materials in plastic containers because they are non-reactive and does not react with water and air.
Teflon, a kind of plastic is used as a coating to manufacture non-stick cookware.Bakelite is a poor conductor of heat and electricity so it is used for making electric switches and handles of the utensils.
Melamine is used for making floor tiles and kitchenware.
Give Examples Which Indicate That Nylon Fibres Are Very Strong.
Nylon is a very strong fibre that is why nylon is used for making parachutes, rock climbing ropes, fishing nets seat belts etc. A nylon thread is elastic and light but actually stronger than a steel wire.
Explain Why Some Fibres Are Called Synthetic.
Some fibres which are not natural (man-made fibres) called synthetic because they are made by chemical processing of petrochemicals. The synthetic fibres are made up of very large units called polymers. Some of the synthetic fibres are rayon, nylon and acrylon.
Explain Why Plastic Containers Are Favoured For Storing Food.
Plastic containers are favoured for storing food for the following reasons:
Plastic containers are light weight so they are easy to handle.
The price of plastic containers is very less as compared to other containers.
They have good strength.
Plastic containers are durable.
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?
Answers Of Important Question
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.
Class 8 Science Chapter 3 Important Questions Set – 1
Define The Term Synthetic Fibre. Mention Also Their Pattern Of Joining With Each Other.
Synthetic fibre: There are some fibres which made from chemical substances, and they do not obtain from plant or animal sources. These are called synthetic fibres. Some examples of synthetic fibres are polyester, nylon and acrylic.
A synthetic fibre is also a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer. The word ‘polymer’ comes from two Greek words; “poly” meaning “many” and “mer” meaning “part/unit”. So, a polymer is made of many repeating units.
Can You Write A Name Of A “Natural Polymer”?
Cotton is a natural polymer, called cellulose. Cellulose is made up of a large number of glucose units.
Name Some Common Articles Made From Fibres.
Generally, shirt, trousers, bed sheets, blankets, curtains, table-cloths, towels and dusters are made from different kinds of fibres.
Why Rayon Is Referred As “Artificial Silk” Or “Man-Made Fibre”? Discuss.
Towards the end of the nineteenth century, scientists were successful in obtaining a fibre having properties similar to that of silk. Such fibre was obtained by chemical treatment of wood pulp. This fibre was called rayon or artificial silk.
Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. Therefore, this fibre is referred as artificial silk or man-made fibre.
Nylon Fibre
Nylon is another man-made fibre. We use many articles 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.
Class 8 Science Chapter 3 Important Questions Set – 2
“In Every Year, Boojho Likes To Wear A Sweater Which Appear To Resemble Like Wool”. Which Type Of Fibre Is Used In His Sweater? Why Do People Choose This Type Of Sweaters?
These are prepared from a type of synthetic fibre, called acrylic.
The wool obtained from natural sources is quite expensive, whereas clothes made from acrylic are relatively cheap. They are available in a variety of colours. Synthetic fibres are more durable and affordable which makes them more popular than natural fibres.
We Should Not Wear Synthetic Clothes While Working In Kitchen Or In The Laboratory”. Why?
Synthetic fibres melt on heating. This is actually a disadvantage of synthetic fibres. If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of the person wearing it. We should, therefore, not wear synthetic clothes while working in in the kitchen or in a laboratory.
Write Down Some Characteristics Of Synthetic Fibre.
Synthetic fibres possess unique characteristics which make them popular dress materials.
i)Synthetic fibres are very strong and durable.
ii) Synthetic fibres are light, wrinkled free and easy to maintain.
iii)Synthetic fibres are less expensive and readily available in the market.
iv) Synthetic fibres are extremely fine and shiny.
v) Synthetic fibres absorb very little water.
vi)Synthetic fibre are not attacked by moths easily.
What Do You Mean By “Thermoplastic” And “Thermosetting Plastic”?
There are some plastic articles which can bend easily while some break when forced to bend. When we add hot water to a plastic bottle, it gets deformed. Such plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics.
Polythene and PVC are some of the examples of thermoplastics. These are used for manufacturing toys, combs and various types of containers.
On the other hand, there are some plastics which when moulded once, cannot be softened by heating. These are called thermosetting plastics.
The Characteristics Of Polyester Fibre
Polyester is another synthetic fibre. Although, polyester (Poly+ester) is actually made up of the repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell.
Fabric made from this fibre does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material. Generally, people love to wearing polyester shirts and other dresses. Terylene is a popular polyester. It can be drawn into very fine fibres that can be woven like any other yarn.
Class 8 Science Chapter 3 Important Questions Set – 3
Bakelite And Melamine Are The Example Of Thermosetting Plastic. Write Down Their Some Features.
Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc. Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used for making floor tiles, kitchenware and fabrics which resist fire.
Why Do People Always Prefer To Choose Plastic Instead Of Using Metals? Explain.
Today if we think of storing a food item, water, milk, pickles, dry food, etc., plastic containers seem most convenient. This is because of their light weight, lower price, good strength and easy handling. Being lighter as compared to metals, plastics are used in cars, aircrafts and spacecrafts, too. Metals like iron get rusted when left exposed to moisture and air. But plastics do not react with water and air. They are not corroded easily. Plastics are poor conductors of heat and electricity. That is why electrical wires have plastic covering, and handles of screw drivers are made of plastic. The list is endless if we start counting articles like slippers, furniture and decoration pieces, etc. Therefore, people always prefer to choose plastic instead of using metals.
Which Type Of Plastic Is Used For Non-Stick Coating On Cook-Wares?
Teflon is a special plastic on which oil and water do not stick. It is used for non-stick coating on cook-wares.
Paheli Wants To Know The Uses Of Plastic In Health-Care Industry”. Will You Help Her?
Plastics find extensive use in the health-care industry. Some examples of their use are the packaging of tablets, many bottles, threads used for stitching wounds, syringes, doctors’ gloves and a number of medical instruments and so on.
Biodegradable And Non-Biodegradable
A material which is not easily decomposed by natural processes is termed as non-biodegradable. Such as plastic. A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable. Such as animals, trees, cotton, jute. All organic compound comes to this category.
Class 8 Science Chapter 3 Important Questions Set – 4
Boojho Wants To Know That Which Type Of Plastic Is Used For The Coating Of Uniforms Of Fireman? Would You Like To Help Him?
Although synthetic fibre catches fire easily, it is interesting to know that the uniforms of firemen have coating of “melamine plastic” to make them flame resistant.
Avoid The Use Of Plastic As For As Possible”. Justify The Statement.
Plastic takes several years to decompose; it is not environment friendly. A material which is not easily decomposed by natural processes is termed as non-biodegradable. Such as plastic. A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable. Such as animals, trees, cotton, jute. All organic compound comes to this category. Plastic causes environmental pollution. Besides, the burning process in the synthetic material is quite slow and it does not get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution. We should use of bags made of cotton or jute instead of plastic bags when we go for shopping. It is better to recycle the plastic waste. Most of the thermoplastics can be recycled. Try to minimise the use of plastic materials. We should develop habits which are environment friendly.
Generally, We See In A Garbage Dump Where Animals Eating Garbage”. How Does Plastic Create Problems For Them?
In the process of eating the food waste from dump of garbage – “they swallow materials like polythene bags and wrappers of food”. The plastic material chokes the respiratory system of these animals, or forms a lining in their stomachs and can be the cause of their death.
How Would You Contribute Towards The Reducing The Use Of Plastic Materials?
Sometimes people are very careless and throw the wrappers of chips, biscuits and other eatables on the road or in parks or picnic places. The polybags carelessly thrown here and there are responsible for clogging the drains, too. Should we not think twice before doing so?
There are some of the steps which contribute towards the reducing the use of plastic materials by us.
i) Avoid the use of plastics as far as possible.
ii) Buy products without a little plastic packaging.
iii) Use bags made of cotton or jute or recycled paper, when you go for shopping.
iv) Collect and dispose of biodegradable and nonbiodegradable waste separately.
v) Do not throw plastic waste in the street on the pavement or in drains.
vi) Try to minimise the use of plastic materials e.g. use a steel lunch box instead of a plastic one.
Do Not Burn Plastic And Synthetic Fabrics
Burning of plastics and synthetic fabrics produces lots of poisonous gases causing air pollution. So, it is not advisable to burn plastic and synthetic fabrics.
Class 8 Science Chapter 3 Important Questions Set – 5
“As A Responsible Citizen Remember The 4R Principle”. Explain The Statement.
The 4 R principle is: 4R means Reduce, Reuse, Recycle and Recover.
1) Reduce: We must reduce the use of resources as possible and save them for the future generation. Reducing the usage is a method of conservation of resources.
2) Reuse: Resources can be reused wherever possible. We need not produce resources on large scale which may lead to exploitation of natural resources. Instead we can reuse them.
3) Recycle: Resources can be recycled wherever possible so that they can be used again and again.
4) Recover: We can recover or restore the resources into their original state, wherever possible.
A Lady Went To A Market To Buy A Blanket. The Shopkeeper Showed Her Blankets Made Up Of Acrylic Fibres As Well As Made Up Of Wool. She Preferred To Buy An Acrylic Blanket”. Can You Guess Why?
Acrylic blankets are cheap, light in weight, more durable and are available in variety of colours and designs. They can be easily washed at home.
Give Example To Show That Plastics Are Non-Corrosive In Nature.
We can store various kinds of chemicals and other materials in plastic containers because they are non-reactive and does not react with water and air.
1) Teflon, a kind of plastic is used as a coating to manufacture non-stick cookware.
2) Bakelite is a poor conductor of heat and electricity so, it is used for making electric switches and handles of the utensils.
3) Melamine is used for making floor tiles and kitchenware.
Despite Being Very Useful, It Is Advised To Restrict The Use Of Plastic”. Why Is It So? Can You Suggest Some Methods To Limit Its Consumption?
It is advised to restrict the use of plastic because of the following reasons:
1) The articles made of plastics are non-biodegradable. They do not decompose (or rot) easily. This causes a great problem in the disposal of plastic waste.
2) The burning of plastic waste gives out harmful gases which pollute the air. So, it is not advisable to dispose of the used plastic articles by burning.
Manufacturing Synthetic Fibres Is Actually Helping Conservation Of Forests
Synthetic fibres are man-made fibres. These fibres are made from petrochemicals. For manufacturing synthetic fibres cutting of trees or killing of animals is not required and we can conserve our natural environment using synthetic fibres. Hence, “manufacturing synthetic fibres is actually helping conservation of forests”.