NCERT Solutions for Class 8 Science Chapter 3 Synthetic Fibres and Plastic

When you purchase clothes, do you ask what it is made up? Chances are yes.

Many clothes are made from materials like polyester and rayon. These are known as synthetic fibres as they are made from petrochemicals. On the other hand, cotton, silk etc are natural fibres as they come from natural sources like plants and animals. Both have their advantages and disadvantages.

The chapter Synthetic Fibres and Plastic of NCERT solutions for class 8 science provides information about the natural and synthetic fibres, their classification, characteristics, plastics, and their effects on the environment.

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Question 1: Explain why some fibres are called synthetic.

Solution: Some fibres are called synthetic because those are man-made. They are prepared in laboratories using chemicals. Examples- nylon, polyester, acrylic.

Question 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.

Solution: Rayon is called semi-synthetic fibre. It is different from synthetic fibres because it is obtained from a natural product (wood pulp). Other synthetic fibres are made in laboratories using chemicals. Rayon also has a silk-like appearance. Due to this, it is also called artificial silk.

Question 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 __________.

Solution:

(a) Synthetic fibres are also called artificial or man-made fibres.

Synthetic fibres are not obtained from natural products. Due to this, they are called artificial fibres. Since they are made in laboratories using chemicals, so they are also called man-made fibres.

(b) Synthetic fibres are synthesised from raw material called petrochemicals.

Synthetic fibres are made from chemicals obtained during petroleum refining called petrochemicals.

(c) Like synthetic fibres, plastic is also a polymer.

Like plastic, synthetic fibres are also formed by polymerisation reactions. Small units of monomers combine in both the cases to form polymer.

Question 4. Give examples which indicate that nylon fibres are very strong.

Solution: Nylon is a strong and durable fibre. Due to this, it is used to make parachutes, fishing nets, sports items, and ropes for rock climbing.

Question 5. Explain why plastic containers are favoured for storing food.

Solution: Plastic containers are preferred for storing food due to following reasons:

(I) They are cheap.

(II) They are easy to handle.

(III) They are strong and durable.

(IV) They are non-corrosive and non-reactive. They do not react with the ingredients of food.

Question 6. Explain the difference between thermoplastic and thermosetting plastics.

Thermoplastic plastics	Thermosetting plastics
Monomers combine in linear manner	Monomers join in cross-linked manner
Melts on heating	Do not melt on heating
Examples- PVC. polythene	Examples- Melamine, Bakelite

Question 7. Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

(b) Electric plugs/switches/plug boards

Solution:

(a) Thermosetting plastics are poor conductors of heat and do not melt on heating. Due to these reasons, they are used to make saucepan handles.

(b) Since, thermosetting plastics are poor conductors of electricity, they are used in making electric plugs, switches, and plugboards.

Question 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, electrical switches.

Solution:

Can be recycled	Cannot be recycled
Plastic toys, carry bags, plastic bowls, plastic covering on electrical wires, plastic chairs	Telephone instruments, cooker handles, ball point pens, electrical switches

Question 9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Solution: In summers, Rana should buy cotton shirts. This is because cotton clothes have more water-absorption properties than synthetic clothes. They can absorb sweat easily.

Question 10. Give examples to show that plastics are non-corrosive in nature.

Solution: Plastics are non-corrosive in nature. The following examples prove this fact:

1. Strong chemicals are stored in plastics rather than metal containers.

2. On keeping plastic toys or other products undisturbed for a long time, their appearance remains the same. They do not corrode in air and moisture.

Question 11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

Solution: The handle of the toothbrush needs to be made of a hard material like plastic while bristles cannot be made of a hard material otherwise it can harm the gums. So, bristles are made using soft and flexible materials like nylon.

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Question 12. ‘Avoid plastics as far as possible’. Comment on this advice.

Solution: Plastics are non-biodegradable in nature. They remain as they remain same for millions of years. The excess use of plastic can be a threat to the environment in the coming years. It can clog the water systems if thrown in water bodies or may entangle the aquatic animals to death. If ingested by mistake by animals can harm them. On burning plastics, they release toxic gases. So, it is advised to avoid plastics as much as possible.

Question 13. Match the terms of column A correctly with the phrases given in column B.

Solution: i-d, ii-c, iii-a, iv-b

Polyester is an example of synthetic fibre. It does not wrinkle easily.

Teflon is an example of the thermosetting plastic. On heating or at a high temperature, it does not melt. So, it is used to make non-stick cookware.

Rayon is a semi-synthetic fibre. It is called so because it is prepared by man using a natural product called the wood pulp.

Nylon is a strong and durable fibre. Due to this, it is used to make parachutes and stockings.

Question 14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Solution: There are two types of fibres; natural (examples-cotton, flax, jute) and synthetic fibres (examples-nylon, polyester, acrylic). Since natural fibres are obtained from plants. This requires cutting down trees in the forests. So, using more synthetic fibres can help conserve forests.

Question 15. Describe an activity to show that thermoplastic is a poor conductor of electricity.

Solution: To prove the fact that thermoplastics are poor conductors of electricity, we can place a thermoplastic in a closed circuit. For this, we need a bulb, connecting wires, battery, thermoplastic polymer (a piece of PVC pipe), and a metal rod piece. On arranging the items in the circuit, we observe that the bulb does not glow in the case of PVC pipe while it glows in the case of the metal piece. This proves that thermoplastics do not allow electricity to pass through them.

Links to Other Resources for Class 8 Science

Other Class 8 Science Related Links
Understanding Structure and Functions of a Cell
Deforestation, Afforestation and Reforestation
Frictional Force Definition, and Types with Example
Compare LPG and Wood as Fuel
Water Pollution Causes and Effects with Example