3. Synthetic Fibres And Plastics Science class 8 exercise Additional Questions With Solutions
3. Synthetic Fibres And Plastics Science class 8 exercise Additional Questions With Solutions ncert book solution in english-medium
NCERT Books Subjects for class 8th Hindi Medium
Chapter Review
Chapter Review:
- Fabrics are made from fibres obtained from natural or artificial sources.
- Fibres are also used for making a large variety of household articles.
- Natural fibres like cotton,wool, silk, etc., are obtained from plants or animals.
- The synthetic fibres, on the other hand, are made by human beings that is why these are called synthetic or man-made fibres.
- Many such small units combine to form a large single unit called a polymer.
- Polymers occur in nature also. Cotton, for example, is a polymer called cellulose.
- Cellulose is made up of a large number of glucose units.
- Such a fibre was obtained by chemical treatment of wood pulp. This fibre was called rayon or artificial silk.
- Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.
- Nylon fibre was strong,elastic and light.It was lustrous and easy to wash.So ,it became very popular for making clothes and parachutes and ropes for rock climbing.
- PET is a very familiar form of polyester. It is used for making bottles,utensils, films, wires and many other useful products.
- Sweaters and shawls or blankets are prepared from another type of synthetic fibre called acrylic.
- All the synthetic fibres are prepared by a number of processes using raw materials of petroleum origin, called petrochemicals.
- Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires.
- Polythene (Poly+ethene) is an example of a plastic. It is used for making commonly used polythene bags.
- Such plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics.examples: toys, combs and various types of containers.
- There are some plastics which when moulded once, can not be softened by heating. These are called thermosetting plastics. examples: bakelite and melamine
- Plastics do not react with water and air. They are not corroded easily. That is why they are used to store various kinds of material.
- Plastic is very light, strong, durable and can be moulded into different shapes and sizes, it is used for various purposes. Plastics are generally cheaper than metals.
- 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.
- Teflon is a special plastic on which oil and water do not stick. It is used for nonstick coating on cookwares.
- A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable
- A material which is not easily decomposed by natural processes is termed as non-biodegradable.
- The 4 R principle is Reduce, Reuse, Recycle and Recover.
Text Book Exercise
Exercise
Q1. Explain why some fibres are called synthetic?
Answer:
Since man-made fibers are obtained by the synthetic of petrochemicals, they are called synthetic fibres.
Q2. Mark ( ) the correct answer:
Rayon is different from synthetic fibres because.
(a) it has a silk like appearance.
(b) it is obtained from wood pulp.
(c) its fibres can also be woven like those of natural fibres.
Answer:
(b) it is obtained from wood pulp.
Q3. Fill in the blanks with appropriate words:
(a) Synthetic fibres are also called ______ or _______ fibres.
(b) Synthetic fibres are synthesised from raw material called ________.
(c) Like synthetic fibres, plastic is also a ________.
Answer:
(a) artificial, man-made.
(b) polymer.
(c) petrochemicals.
Q4. Give examples which indicate that nylon fibres are very strong.
Answer:
They are used to make Parachutes,and ropes for rockclimbing.
Q5. Explain why plastic containers are favoured for storing food.
Answer:
The three main advantages of using plastic containers for storing food are:
(I) plastic has light weight,
(II) good strength,and
(III) are easy to handle.
Q6. Explain the difference between the thermoplastic and thermosetting plastics.
Answer:
Thermoplastics Plastic:
(I) These are the plastics which gets deformed easily on heating and can be bent easily.
Examples: Polythene and P.V.C.
(II) These are used for manufacturing toys, combs, car grills and various types of containers.
Thermosetting plastics:
(I) These are the plastics which when moulded once,cannot be softened by heating.
Examples: Bakelite and melamine.
(ii) (a) Bakelites are used for making electrical switches,handles of various utensils,etc.
(b)Melamines are used for making floor tiles,kitchen-wares and fabrics,which resist fire.
Q7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Answer
:(a) As baklite (a kind of thermosetting plastic) is a bad conductor of heat, therefore, saucepan handles are made up of it.
(b) Bakelite (a kind of thermosetting plastics) is also a bad conductor of electricity, so these electricity appliances are made up of it.
Q8. Categorise the following materials into ‘can be recycled’ and ‘cannot be recycled’: Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
Answer:
(i) Can be recycled: Telephone instruments, plastics toys, ball point pens, plastics bowls.(As these are thermoplastics, so these can be recycled).
(II) Cannot be recycled: Cooker handles,carry bags, plastic covering on electric wire, plastic chairs, etc. (As these are thermosetting plastic, these cannot be recycled).
Q9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason?
Answer:
I would advise Rana to buy cotton shirts absorb the sweat and thus endorse cooling, Besides, they also provide aeration.
Q10. Give examples to show that plastics are noncorrosive in nature?
Answer:
The plastics are noncorrosive, that is, do not react or do not have chemical reaction with the materials contained in it. That is why many containers like bucket, mug, water bottles, food containers are made by using plastics.
Q11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer?
Answer:
The handles and bristles of a toothbrush should be made of a material which has light weight, good strength and is hygine. But the bristles should be soft enough so that they do not harm gums while the handle should be quite stuff so that it may not get bent while brushing.
Q12. ‘Avoid plastics as far as possible’. Comment on this advice?
Answer:
Since plastic takes several years to decompose, it is not decompose, it is not enviorment friendly. It causes enviormental pollution. Besides, its burning releases lots of poisoms fumes into the atmosphere causing air pollution. So, we should aviod the use of plastic as far as possible.
Q13. Match the terms of column A correctly with the phrases given in column B.
(i) Polyester (a) Prepared by using wood pulp
(ii) Teflon (b) Used for making parachutes and stockings
(iii) Rayon (c) Used to make non-stick cookwares
(iv) Nylon (d) Fabrics do njot wrinkle easily.
Answer:
(i)-(d) (ii)-(c) (iii)-(a) (iv)-(b)Q14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment?
Answer: The synthetic fibres are made up of petrohemicals. So, manufacturing synthetic fibres does not depend upon plants. These synthetic fiders cater the need of people upto great extent. Thus, the forests are not destroyed to manufacture clothes and other items. So, indirectly, we can come to a conclusion that manufacturing synthetic fiber is actually helping conservation of forests.
Q15. Describe an activity to show that thermoplastic is a poor conductor of electricity?
Answer: If we make an experimental set up using copper wire, a thermoplastic object, a bulb and a cell, as shown in the figure given below, the bulb does not glow.
however, if thermoplastic object is removed from the circuit, the bulb glows up. This shows that thermoplastic objects are bad conductor of electricity.
Text Book Exercise
Text Book Exercise:
9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer: I wiil advice rana to wear cotton clothes. Cotton clothes, which are natural fabric, do not contain heat, instead they reflect out heat. Besides, they also provide aeration. So, during summar, we prefer cotton clothes, and not the synthetic clothes.
10. Give examples to show that plastics are noncorrosive in nature.
Answer: The plastics are non-corrosive, that is, they do not react or do not have chemical reaction with the materials contained in it. That is many containers are made up of plastics.
11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Answer:Yes, because both should be made of the material, which is light in weight, have good strenght and hygienic.
12. ‘Avoid plastics as far as possible’. Comment on this advice.
Answer: Since plastic takes serval years to decompose, it is not enviroment frindly. It causes enviromental pollution. Besides, the buring process in the synthetic material is quit slow and it does not burn completelely. in the process it releases lots of poisonous fames into the atmosphere causing air pollution. So, we should avoid the use of plastics as far as possible.
13. Match the terms of column A correctly with the phrases given in column B.
(i) Polyester (a) Prepared by using wood pulp
(ii) Teflon (b) Used for making parachutes and stockings
(iii) Rayon (c) Used to make non-stick cookwares
(iv) Nylon (d) Fabrics do not wrinkle easily
Answer:
(i) (d), (ii) (c), (iii) (a), (iv) (b).
14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’.
Answer. The synthetic fibres are made up of petrochemicals.So, the manufacture of synthetic fibres does not depend upon plant and trees. These synthetic fibres cater the need of people upto great extent.Thus the forests are not destroyed to manufacture clothes and other items. So, indirectly, we can come to a conclusion that manufacturing synthetic fibres is actually helping conversation of forests.
15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer: If we make an experimental set up using copper wire, a thermoplastic object, a bulb and a cell, as shown in the figure given below, the bulb does not glow.
However, if the thermoplastic object is removed from the circuit, the bulb glow up. This shows that thermoplastics object are bad conductor of electricity.
Additional Questions With Solutions
Additional Questions With Solutions
Que: Name the sources of fibres, by which are fabrics made?
Ans: Natural fibres and artificial fibres.
Que: Name the some natural fibres.
Ans: (i) Cotton (ii) wool (iii) silk
Que: Name some artificial or synthetic fibres.
Ans: (i) Rayon (ii) Nylon (iii) polyester and (iv) Acrylic
Que: What are synthetic fibres?
Ans: The fibres which are made by the human beings is called synthetic fibres. As Rayon, Nylon, polyester and Acrylic
Que: What is polymer?
Ans: The small units of fibres which is actually a chemical substance, such many small units combine to form a large single units is called a polymer. Ex. Cellulose, Nylon, polyester etc.
Que: Name a natural polymer.
Ans: Cellulose.
Que: Write the property of Rayon.
Ans: Rayon is the man-made fibre which is obtained by chemical treatment of wood pulp.
Properties:
(i) It is cheaper than silk.
(ii) It can be woven like silk fibre.
(iii) It can also be dyed in a wide variety of colours.
Que: Write the three property of Nylon.
Ans: Nylon is also man-made fibre. It was prepared from coal, water, and air. Properties;
(i) It is strong, elastic and light.
(ii) It is lustrous and easy to wash.
Que: Write the use of nylon?
Ans: Nylon is used for making parachutes and ropes for rock climbing. A nylon thread is an actually stronger than a steel wire. It is also used for making cloth.
Que: Name some synthetics fibers which are used for wearing.
Ans: Polyester and Terylene.
Que: What is PET and write its uses?
Ans: PET is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.
Que: What is acrylic?
Ans: The wool which are actually not made from natural wool. These are prepared from another type of synthetic fibre called acrylic.
Que: What are thermoplastics?
Ans: Such plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics.
Que: What are thermosetting plastics?
Ans: Some plastics which when moulded once, cannot be softened by heating. These are called thermosetting plastics.
Que: Give examples to show that plastics are noncorrosive in nature.
Ans: The plastic is noncorrosive in nature because of it doesn’t react to air and water.
Additional Questions With Solutions
Additional Questions With Solutions
Que: Write the differences between thermoplastics and thermosetting plastic.
Ans:
Thermoplastics plastic |
Thermosetting plastic. |
(i) It can be bent. (ii) It gets deformed easily on heating. (iii) Examples; polythene and PVC. |
(i) It can’t be bent. (ii) It can’t be softened by heating. (iii) Example; Bakelite and melamine. |
Que: What is Bakelite?
Ans: Bakelite is a thermoplastic. It is a polymer which is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc.
Que: What is melamine?
Ans: 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.
Que: Explain why plastic containers are favoured for storing food.
Ans: plastic containers are favoured for storing food. This is because of their light weight, lower price, good strength and easy handling. Being lighter as compared to metal.
Que: Give examples which indicate that nylon fibres are very strong.
Ans: Nylon is also used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.
Que: Why are the handles of screw driver and fry pan made of plastic?
Ans: Because plastics are poor conductors of heat and electricity.
Que: Why is the disposal of a plastic material major problem?
Ans: Toxin produced by plastic is major problem to remove from environment. As on burning it produces toxic smoke and disposal in soil it produce toxic effect. So it can’t be removed easily.
Que: What is biodegradable?
Ans: A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable.
Example: peels of vegetables and fruits, paper, wood , cotton clothes etc.
Que: What is non-biodegradable?
Ans: A material which is not easily decomposed by natural processes is termed as non-biodegradable. For Example: Tin aluminium plastic bags and other metals.
Que: Explain why some fibres are called synthetic.
Ans: Some fibres are called synthetic because they are made by human beings.
Que: Mark the correct answer.
Rayon is different from synthetic fibres because
- It has a silk-like appearance.
- It is obtained from wood pulp.
- Its fibres can also be woven like those of natural fibres.
Ans:
- It is obtained from wood pulp.
Que: Give examples which indicate that nylon fibres are very strong.
Ans: Parachutes and nylon ropes are used for rock climbing.
Que: Name the plastic whose sheets are used for packing liquids.
Ans: Polythene.
Que: Why is teflon used as tape for sealing purpose?
Ans: Becausee of its toughness, teflon is used as tape for sealing purpose.
Que: Name the first fully synthetic fibre.
Ans: Nylon.
Que: Why nylon is used for making parachutes?
Ans: Nylon is used for making parachutes, because it is very strong, elastic and light.
Que: Name the material used for making ropes for rock climbing.
Ans: Nylon.
Que: What is polyester?
Ans: Polyester is made up of the repeating units of an ester.
Que: Name the plastic used for making polythene bags.
Ans: Polythene bag is made of plastic which is a polymer of ethene.
Que: What name is given to plastics which can be re-set a number of times?
Ans: Thermoplastics.
Que: Classify the following into thermosetting and thermoplastics-combs, bakelite, melamine, toys.
Ans: Thermosetting – bakelite, melamine
Thermoplastics – combs, toys
Que: Why are the chemicals in the laboratory stored in plastic containers ?
Ans: Plastics are non-reactive, so they can be used for storing chemicals.
Que: Can you store pickles in plastic containers ? Why ?
Ans: Plastics are non-reactive, so pickles can be stored in them.
Que: Why are the electric wires covered with plastic ?
Ans: Plastic is a poor conductor of electricity, therefore, the wires are covered with it.
Que: Why do we use plastic cookwares in microwave ovens?
Ans: We use plastic cookware in microwave ovens, because they are not affected by heat but the food is cooked.
Que: Tin takes about 100 years to degenerate. Is it biodegradable or non-biodegradable?
Ans: Tin is non-biodegradable.
Que: Is it advisable to use recycled plastic containers for storing food?
Ans: No, we should not use recycled plastic containers for storing food because they contain colouring agents.
Que: As a responsible citizen, what are the 4R’s we should remember?
Ans: Reduce, Reuse, Recycle and Recover.
Que: Aperson has to make a non-stick pan. He has three types of plastic-Bakelite, Teflon and PVC. Which plastic will he use for coating and why?
Ans: The person will use Teflon because it is not affected by heat and does not react chemically with other substances.
Que: Explain the difference between thermoplastic and thermosetting plastics.
Ans:
Thermosetting | Thermoplastic |
(i) These plastics can be moulded and (ii) e.g.,Bakelite and melamine. |
(i) These plastics can be moulded and reset a number of times. (ii) e.g. Polythene and PVC. |
Que: Differentiate between natural and synthetic fibres.
Ans: Natural fibres are obtained from nature, e.g., cotton whereas synthetic fibres are made by man, e.g., nylon.
Que: How is rayon made? Give one advantage of using rayon.
Ans: Rayon is obtained from wood pulp by treating it chemically. It is cheaper than silk, but can be woven like silk fibre.
Que: Is nylon fibre so strong, that we can use it to make parachutes ?
Ans: Yes, nylon is very strong and it can be used for making parachutes.
Que: Give some uses of PET.
Ans: PET is used for making bottles, utensils, fibres and wires.
Que: Give the composition of Polycot and Polywool.
Ans: Polycot is a mixture of polyester and cotton, Poly wool is a mixture of polyester and wool.
Que: What properties of plastics make it useful for many things?
Ans: Plastics can be recycled, reused, coloured, melted, rolled into sheets or made into wires, so they are very useful.
Que: Why is melamine used for making kitchenware?
Ans: Melamine resists fire and can tolerate heat better than other plastics. So, it is used for making kitchenware.
Que: Buckets made up of plastics are better. Why?
Ans: Buckets made up of plastic are better because they are light, strong and durable.
Que: Differentiate between biodegradable and non-biodegradable materials.
Ans:
Biodegradable Materials | Non-biodegradable Materials |
(i) A meterial which gets decomposed through natural processes, such as action of bacteria. (ii) e.g., cotton or jute. |
(i) A material which does not get decomposed by natural processes. (ii) e.g., plastics. |
Que: Should the handle and bristles of a tooth brush be made of the same material ? Explain your answer.
Ans: No, the handle and bristles of tooth brush cannot be made of the same plastic. The handle is hard but the bristles are soft and flexible.
Que: Give three advantages of polythene over natural materials.
Ans: Three advantages of polythene over natural materials are :
- It is strong but flexible.
- Can be rolled into sheets.
- Water resistant.
Que: Give one use each of bakelite, nylon and acrylic.
Ans: Bakelite is used for making plugs and switches. Nylon is used in textile industry to produce clothes. Acrylic is used as a substitute of natural wool for knitting sweaters, blankets etc.
Que: Fill in the blanks with appropriate words.
1. Synthetic fibres are also called ……….. or ……….
2. Synthetic fibres are synthesised from raw material called …………
3. Like synthetic fibres, plastic is also a …………..
Ans:
- artificial, man-made
- mono or petrochemicals
- polymers.
Que: Explain why plastic containers are favoured for storing food.
Ans: Food can be stored in plastic containers because
- Plastics are non-reactive.
- Plastics are light and strong.
- Plastics are durable.
Que: Explain why the following are made of thermosetting plastics:
1. Saucepan handles
2. Electric plugs/switches/plug boards.
Ans:
1. Saucepan handles are made of thermosetting plastics because they are bad conductors of heat.
2. Electric plugs/switches/plug boards are made of thermosetting plastics because they are bad conductors of electricity.
Que: Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material ? Advice Rana, giving your reason.
Ans: Rana should buy cotton shirts. Cotton clothes are preferred in summer because they absorb sweat and the person feels cool whereas synthetic materials do not absorb sweat and the person feels uncomfortable.
Que: Give examples to show that plastics are noncorrosive in nature.
Ans:
- Buckets made of iron get rusted but those made of plastic are not rusted.
- Food can be stored in plastic containers, as they are resistant to chemicals in the food
- Teflon coated pans are used instead of metallic as it doesnot react with chemicals in the food.
Que: Give three advantages of rayon.
Ans: Advantages of rayon are :
- It is cheap.
- It can be dyed in many colours.
- It can be woven like silk.
Que: What are the advantages of nylon?
Ans: Nylon fibre is strong, elastic and light. It is lustrous and easy to wash.
Que: Give some uses of nylon.
Ans: Nylon can be used for making socks, ropes, tents, toothbrushes, sleeping bags, curtains, parachutes and ropes for rock climbing.
Que: What are the advantages of using fabrics made of polyester?
Ans: Fabrics made of polyester
- do not get wrinkled easily
- are easy to wash,
- easy to maintain.
Que: Why people prefer to wear acrylic sweaters than pure wool sweaters?
Ans: Acrylic sweaters are cheaper and easy to maintain. They are available in many colours.
Que: What are the disadvantages of wearing synthetic fabrics?
Ans: Synthetic fabric catches fire very easily. It melts and sticks to the body of the person wearing it. During summers, synthetic fibres do not absorb sweat and a person wearing it feels uncomfortable.
Que: Give the characteristics of synthetic fibres.
Ans: Synthetic fibres dry up soon, are durable, less expensive, readily available and easy to maintain.
Que: Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.
Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
Ans:
Can be recycled | Non-biodegradable Materials |
Toys, carry bags, plastic bowls, plastic covering on electrical wires, plastic chairs. | Telephone instruments, cooker handles, electric switches, ball point pens, electrical switches. |
Que: Match the terms of Column A correctly with the phrases given in Column B.
Column A | Column B |
(a) Polyester (b) Teflon (c) Rayon (d) Nylon |
(i) Prepared by using wood pulp. (ii)Used for making parachutes and stockings. (iii) Used to make non-stick cookwares. (v) Fabrics do not wrinkle easily. |
Ans:
Column A | Column B |
(a) Polyester | (iv) Fabrics do not wrinkle easily. |
(b) Teflon | (iii) Used to make non-stick cookwares. |
(c) Rayon | (i) Prepared by using wood pulp. |
(d) Nylon | (ii) Used for making parachutes and stockings. |
Que: ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
Ans: The said statement is correct to a certain extent. The forests would be conserved if synthetic fibres are used, but other effects of synthetic fibres are more harmful. Disposal of synthetic fibres causes lot of environmental pollution. When synthetic fibres bum, lot of smoke is produced.
Que: ‘Avoid plastics as far as possible’. Comment on this advice.
Ans: Plastics are very useful, but it causes serious environmental and health concern :
- Plastics are non-biodegradable.
- Careless disposal of plastic bags, chokes, drains and blocks the soil.
- If eaten by cows, it can kill them.
- Plastic bags can also contaminate foodstuffs due to poisonous dyes getting absorbed into food
Que: How is plastic useful in healthcare industry?
Ans: In healthcare, plastics are used
- for packaging of tablets
- as threads for stitching wounds
- in syringes
- doctor gloves
- for making a number of medical instruments.
Que: “Even though plastics are very useful, they are not environment friendly.” Justify the statement.
Ans: Plastics are very useful, but their disposal is a big problem. Plastics are non-biodegradable and take many years to decompose. They release a lot of poisonous fumes, when burnt so they cause environmental pollution.
Que: Give methods by which pollution due to plastics can be solved.
Ans: Pollution due to plastics can be solved by following methods :
- Avoid the use of plastics as far as possible.
- Use bags, made of jute or cloth.
- Biodegradable and non-biodegradable wastes should be separated and disposed off separately.
- Plastics should be recycled and reused.
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Science Chapter List
1. Crop Production And Management
2. Microorganisms : Friend And Foe
3. Synthetic Fibres And Plastics
4. Materials : Metals And Non-Metals
5. Coal And Petroleum
6. Combustion And Flame
7. Conservation of Plants And Animals
8. Cell - Structure and functions
9. Reproduction in animals
10. Reaching the age of adolescence
11. Force And Pressure
12. Friction
13. Sound
14. Chemical Effects of Electric Current
15. Some Natural Phenomena
16. Light
17. Stars And The Solar System
18. Pollution of Air and Water
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