SCIENCE CLASS 8 CHAPTER 3 SYNTHETICS FIBRES AND PLASTICS

SCIENCE CLASS 8 CHAPTER 3

SYNTHETIC FIBRES AND PLASTICS

EXERCISES

Question number 1

Explain why some fibres are called synthetic.

Answer number 1

Some fibres are called synthetic fibres because these are man made fibres prepared by using chemical substances. Synthetic fibres are nylon, rayon, acrylic, polyester etc.

Question number 2

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 number 2

(b) it is obtained from wood pulp.

Question number 3

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 number  3

(a) artificial, manmade
(b) petrochemicals
(c) polymer

Question number 4

Give examples which indicate that nylon fibres are very strong.

Answer number 4

1. Parachutes and ropes of rock climbing are made of nylon because of its strongness.
2. Nylon is used in making accessories like rackets.
3.Nylon is used in making scat belt, fishing nets and tyre card.

Question number 5

Explain why plastic containers are favoured for storing food.

Answer number 5

Plastic containers  are used for storing food because it is non - reactive and does not react with the ingredients of food items.

Question number 6

Explain the difference between the thermoplastic and thermosetting plastics.

Answer number  6

Thermosetting plastic

1.Thermosetting plastic cannot be bent.
2.On heating thermosetting plastic, it cannot be softened. because of this it cannot be reshaped.

Thermoplastic

1.Thermoplastic can be bent easily.
2.On heating the thermoplastic, it become softened and can be molded and reshaped easily.

Question number 7

Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards

Answer number 7

(a) Thermosetting plastic are bad conductor of heat because of having these property saucepan handles are made of thermosetting plastic and on heating these plastic do not get softened.

(b) Thermosetting plastic are bad conductor of heat and electricity. Because of having these property it is used for making electric plugs, switches, plugs boards etc.

Question number 8

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 and electrical switches.

Answer number 8

Can be recycled          Cannot be recycled
1.Plastic chair             1.Cooker handles
2.Plastic bowl             2.Electrical switches
3.Plastic toys               3.Telephone
4.The plastic covering
on electrical wires
5.Carry bags
6.Ballpoint pens

Question number 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 number 9

Rana should buy a cotton shirt for the summer 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 and it evaporate. Thus it helps in cooling our body. Synthetic materials are not having this property.

Question number 10

Give examples to show that plastics are non corrosive in nature.

Answer number 10

Plastic do not reacts with water, air. They are not corroded easily even if they come in contact with strong chemicals. For example, the cleaning chemical are stored in plastic bottles, instead of the metal container.

Question number 11

Should the handle and bristles of a tooth brush be made of the same material? Explain
your answer.

Answer number 11

The handle and bristles of a toothbrush should not be made of the same material as the handle of the toothbrush should be strong to hold. The bristles should be soft and flexible because its gives friction to gum while cleaning the teeth.

Question number 12

‘Avoid plastics as far as possible’. Comment on this advice.

Answer number 12

We should avoid plastics as far as possible because plastic are non biodegradable in nature. Once comes into the environment they cause pollution. They can't be destroyed and remains in nature forever. If burnt they release poisonous gases.
 Because of the demerits of plastic, it should be avoid as far as possible.

Question number 13

Match the terms of column I correctly with the phrases given in column II.
Column I                 Column II
(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 number 13

Match the terms of column I correctly with the phrases given in column II.
Column I                Column II
(i) Polyester      (d) Fabrics do not wrinkle
                            easily
(ii) Teflon          (c) Used to make non-stick
                            cookwares
(iii) Rayon         (a) Prepared by using
                            wood pulp
(iv) Nylon          (b) Used for making
                            parachutes and stockings

Question number 14

‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Answer number 14

The manufacturing of synthetic fibres is helpful in the conservation of forests because for natural fibres raw material is obtained from the plants which required cutting of lots of trees. Hence manufacturing of synthetic fibres helpful in the conservation of forests.

Question number 15

Describe an activity to show that thermoplastic is a poor conductor of electricity.

Answer number 15

In order to prove that thermoplastic is a poor conductors of electricity the under mention experiment is to be done. For the experiment one piece of plastic material is to be taken and its both end should be connected to a battery and bulb per the diagram. When current pass through the circuit the bulb does not glow it prove that thermoplastic are poor conductor of electricity.

IMPORTANT QUESTIONS AND ANSWERS

A. Very Short Answer Questions

Q1. What are synthetic fibres?

Answer: Synthetic fibres are man-made fibres produced through chemical processes. Examples include nylon, polyester and acrylic.

Q2. What are natural fibres? Give two examples.

Answer: Natural fibres are obtained from plants or animals. Examples include cotton and wool.

Q3. Name four types of synthetic fibres.

Answer: The four main types are:

1. Rayon

2. Nylon

3. Polyester

4. Acrylic

Q4. What is rayon?

Answer: Rayon is a man-made fibre prepared from chemically processed cellulose, usually obtained from wood pulp. It is also called artificial silk.

Q5. What is nylon?

Answer: Nylon is a synthetic fibre known for its strength, elasticity and durability.

Q6. What is polyester?

Answer: Polyester is a synthetic fibre that is strong, wrinkle-resistant and easy to maintain. Terylene is an example of polyester.

Q7. What is acrylic?

Answer: Acrylic is a synthetic fibre that resembles wool and is commonly used to make sweaters, blankets and shawls.

Q8. What are plastics?

Answer: Plastics are materials made mainly from polymers that can be moulded into different shapes. Many plastics are synthetic.

Q9. What is a polymer?

Answer: A polymer is a large molecule made up of many repeating smaller units called monomers.

Q10. What is plasticity?

Answer: Plasticity is the ability of a material to be moulded into a desired shape and retain that shape.

B. Short Answer Questions

Q11. Why are synthetic fibres popular?

Answer: Synthetic fibres are popular because they are generally strong, durable, lightweight, easy to maintain and often less expensive than some natural fibres.

Q12. Write three uses of rayon.

Answer: Rayon is used for:

1. Making clothes and dresses.

2. Manufacturing bed sheets and curtains.

3. Producing certain carpets and furnishing materials.

Q13. Write three uses of nylon.

Answer: Nylon is used for:

1. Making ropes and fishing nets.

2. Manufacturing parachutes.

3. Making toothbrush bristles and some fabrics.

Q14. Why is nylon used for making ropes and parachutes?

Answer: Nylon is strong, lightweight and resistant to wear. These properties make it suitable for ropes and parachutes.

Q15. Why is acrylic used as a substitute for wool?

Answer: Acrylic resembles wool in appearance and provides warmth. It is commonly used to make sweaters, blankets and winter clothing.

Q16. Why should we not wear synthetic clothes while working near fire?

Answer: Synthetic fibres may melt on heating and stick to the skin, causing serious burns. Cotton clothing is generally a safer choice near fire, although all clothing can burn.

Q17. What are the advantages of polyester?

Answer: Polyester has several advantages:

• It is strong and durable.

• It dries quickly.

• It resists wrinkles.

• It is easy to wash and maintain.

• It is widely used in clothing and home furnishings.

Q18. What is the difference between thermoplastics and thermosetting plastics?

Answer:

Thermoplastics	Thermosetting plastics
They soften on heating and can be reshaped.	They cannot be softened and reshaped easily after setting.
They can often be remoulded.	They retain their shape when reheated within normal use conditions.
Examples: polythene and PVC.	Examples: Bakelite and melamine.

Q19. Why is Bakelite used for electrical switches?

Answer: Bakelite is a thermosetting plastic that is a poor conductor of electricity and can withstand heat reasonably well. Therefore, it is suitable for making electrical switches and plug boards.

Q20. Why is melamine used for making kitchenware?

Answer: Melamine is heat-resistant and durable. It is used to make certain plates, bowls and other kitchenware.

C. Long Answer Questions

Q21. Explain the differences between natural and synthetic fibres.

Answer:

Natural fibres	Synthetic fibres
Obtained from plants or animals.	Manufactured through chemical processes.
Examples include cotton, jute and wool.	Examples include nylon, polyester and acrylic.
Some natural fibres absorb moisture well.	Many synthetic fibres dry quickly and resist wrinkles.
Their properties vary according to the source.	Their properties can be designed for particular uses.

Q22. Explain the main types of synthetic fibres and their uses.

Answer:

1. Rayon: Made from processed cellulose. It is used in clothes, curtains and furnishing materials.

2. Nylon: Strong and lightweight. It is used in ropes, parachutes, fishing nets and textiles.

3. Polyester: Durable and wrinkle-resistant. It is used in clothes, bedsheets and curtains.

4. Acrylic: Resembles wool. It is used in sweaters, shawls and blankets.

Q23. Explain the advantages and disadvantages of synthetic fibres.

Answer:

Advantages:

• Generally strong and durable.

• Lightweight and easy to maintain.

• Often dry quickly.

• Many are resistant to wrinkles.

• Available in a wide variety of colours and textures.

Disadvantages:

• Some can melt and stick to the skin when exposed to high heat.

• Many absorb less moisture than cotton.

• Most conventional synthetic fibres do not biodegrade easily.

• Their production and disposal can contribute to environmental pollution and microplastic contamination.

Q24. Explain the harmful effects of plastics on the environment.

Answer: Plastics can harm the environment in several ways:

1. Many plastics take a very long time to break down.

2. Plastic waste can block drains and contribute to flooding.

3. Animals may swallow plastic waste or become entangled in it.

4. Plastic litter can pollute rivers, lakes and oceans.

5. Some plastics break into tiny particles called microplastics.

6. Burning plastics in the open can release harmful pollutants.

Q25. What steps can we take to reduce plastic pollution?

Answer:

1. Carry reusable cloth bags instead of single-use plastic bags.

2. Use reusable bottles and containers.

3. Avoid unnecessary single-use plastic products.

4. Reuse plastic items when safe and practical.

5. Segregate waste and send recyclable plastics to appropriate recycling facilities.

6. Never burn plastic waste in the open.

7. Participate in cleanliness and awareness campaigns.

D. Fill in the Blanks

1. Fibres made by humans through chemical processes are called synthetic fibres.

2. Rayon is also known as artificial silk.

3. Nylon is used for making parachutes and ropes.

4. Acrylic resembles wool.

5. Polyester is widely used in clothing.

6. Plastics are made mainly from substances called polymers.

7. Bakelite is a thermosetting plastic.

8. Polythene is a thermoplastic.

9. Many plastics are non-biodegradable.

10. Reducing, reusing and recycling are important ways to manage plastic waste.

E. True or False

1. Nylon is a natural fibre. — False

2. Rayon is made from processed cellulose. — True

3. Acrylic resembles wool. — True

4. All plastics are biodegradable. — False

5. Bakelite is a thermosetting plastic. — True

6. Synthetic clothes are always safe to wear near fire. — False

7. Polyester is used for making clothes. — True

8. Plastic waste can harm animals. — True

9. Thermoplastics can often be softened and reshaped by heating. — True

10. Burning plastic waste in the open is a safe disposal method. — False

F. Important NCERT Exercise-Based Questions

Q26. Give examples of objects made from plastics.

Answer: Buckets, bottles, toys, pipes, electrical switches, containers and chairs are examples of objects made from plastics.

Q27. Why are plastic containers commonly used for storing food?

Answer: Suitable food-grade plastic containers are lightweight, durable, easy to clean and resistant to breaking. They should be used according to their intended temperature and food-contact guidelines.

Q28. Why are plastics used in electrical appliances?

Answer: Many plastics are poor conductors of electricity and are lightweight and durable. Therefore, they are used for insulation and protective coverings in electrical appliances.

Q29. Why should we avoid using plastic bags?

Answer: Plastic bags can cause pollution, block drains and harm animals. Reusable cloth or other suitable reusable bags help reduce plastic waste.

Q30. What is the difference between biodegradable and non-biodegradable materials?

Answer:

• Biodegradable materials: Materials that microorganisms can break down naturally under suitable conditions. Examples include vegetable peels and paper.

• Non-biodegradable materials: Materials that do not break down easily through natural biological processes. Examples include many conventional plastics.

Q31. Why should plastic waste be separated from other waste?

Answer: Separating plastic waste makes collection, sorting and recycling easier. It also reduces the amount of plastic reaching landfills and the natural environment.

Q32. What is the 5R approach to reducing waste?

Answer: A useful waste-reduction approach is:

• Refuse unnecessary items.

• Reduce consumption.

• Reuse items whenever possible.

• Repair products to extend their life.

• Recycle suitable materials.

G. Quick Revision: Important Terms

Term	Meaning
Synthetic fibre	Man-made fibre produced through chemical processes
Rayon	Fibre made from processed cellulose
Nylon	Strong synthetic fibre
Polyester	Durable, wrinkle-resistant synthetic fibre
Acrylic	Synthetic fibre resembling wool
Polymer	Large molecule made of repeating smaller units
Thermoplastic	Plastic that can be softened and reshaped by heating
Thermosetting plastic	Plastic that cannot be easily remoulded after setting
Biodegradable	Capable of being broken down by biological processes
Non-biodegradable	Not easily broken down by natural biological processes

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ALSO SEE SOLUTIONS OF FOLLOWING CHAPTERS :

Crop Production And Management
Microorganisms - Friend And Foe
Synthetic Fibre And Plastic

Material : Metals And Non - Metals

Coal And Petroleum

Some Natural Phenomena

Chemical Effects of Electric Current

Our Home: Earth, a Unique Life Sustaining Planet

How Nature Works in Harmony

Reaching the Age of Adolescence

Reproduction in Animals

Conservation of Plants and Animals

COMBUSTION AND FLAME

STRUCTURE AND FUNCTIONS