Living Science 2019 Solutions for Class 8 Science Chapter 3 Synthetic Fibres And Plastics are provided here with simple step-by-step explanations. These solutions for Synthetic Fibres And Plastics are extremely popular among Class 8 students for Science Synthetic Fibres And Plastics Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science 2019 Book of Class 8 Science Chapter 3 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science 2019 Solutions. All Living Science 2019 Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

Page No 40:

Question 1:

There is a different between the raw materials used in rayon and other synthetic fibres like nylon or polyester. What is the difference?

Answer:

Rayon is a regenerating natural fiber (cellulose fiber), which is made from the wood pulp. Whereas nylon or polyester, fibers are purely synthetic polymers, made entirely from chemicals. 
 

Page No 40:

Question 2:

The Prefix 'poly' means 'many' for example, 'polygon' means a figure with many sides. What is the significance of the prefix 'poly' in 'polyester'?

Answer:

A polymer is made of two words, 'poly' means many and 'mer' means unit or part. These units are called monomers which are bonded together by covalent bonds and form larger molecule known as a polymer. For example, polythene is made of many ethene monomer units.

Page No 40:

Question 3:

Synthetic fibres are strong, elastic, light, wrinkle-resistant, and easy to wash and dry. Even with so many advantages, we do not wear clothes made of pure synthetic fibres, but a mixture of synthetic and natural fibres. Why is this necessary?

Answer:

Even with so many advantages, we do not wear clothes made of pure synthetic fibres because:

1. They do not absorb sweat or water and they stick to the body, which makes them uncomfortable to wear in hot humid conditions.
2. They catch fire very readily, they melt on heating and stick to the body. Therefore, they can cause severe burn injuries.



Page No 43:

Question 1:

The molecular structures of synthetic fibres and plastics have one common feature. What is it?

Answer:

The common feature between the molecular structures of synthetic fibre and plastics is that they both are polymers and are made up of a long chain of monomers. Plastics are basically synthetic fibres but all synthetic fibres are not plastics.

 

Page No 43:

Question 2:

Bakelite and polythene are both plastics. However, there is one major difference in their nature. What is the difference?

Answer:

Bakelite is a thermosetting polymer i.e. they can be softened by heating only once i.e. once they are moulded and harden on cooling, they cannot be softened again. Whereas, polythene is a thermoplastic polymer i.e. softening and hardening can be repeated again and again.
 

Page No 43:

Question 3:

Can bacteria break down plastics?

Answer:

Plastics are non-biodegradable i.e. they cannot be decomposed by the microorganisms such as bacteria.



Page No 44:

Question 1:

Which of these is a natural fibre?
(a) rayon
(b) cotton
(c) nylon
(d) polyester

Answer:

(b) cotton
Natural fibres are greatly elongated hair-like substances obtained from plants or animals. They can be spun into filaments, threads or ropes. Cotton fibre is almost pure cellulose that grows in a protective capsule around the seeds of cotton plants.

Page No 44:

Question 2:

Which of these is a fibre derived from chemicals?
(a) rayon
(b) cotton
(c) nylon
(d) silk

Answer:

(c) nylon
Fibres derived from chemicals are polymers. They do not occur naturally but are produced entirely in chemical plants or laboratories. Nylons are man-made polymer fibres.

Page No 44:

Question 3:

Which of these fibres is made from a raw material obtained from plants?
(a) rayon
(b) nylon
(c) terylene
(d) polyester

Answer:

(a) rayon
Rayon is a manufactured regenerated cellulose fibre that is made from purified cellulose, primarily from wood pulp.

Page No 44:

Question 4:

Which of these is a thermosetting plastic?
(a) polystyrene
(b) bakelite
(c) polythene
(d) polyvinyl chloride

Answer:

(b) bakelite
Thermosetting plastics are rigid and heavily cross-linked polymers. They cannot be remoulded once they set. Bakelite is a thermosetting phenol formaldehyde resin.

Page No 44:

Question 5:

Which of these plastics is a polymer?
(a) bakelite
(b) polystyrene
(c) polythene
(d) all of these

Answer:

(d) all of these
A polymer is a macromolecule composed of many repeated subunits, known as monomers. Bakelite is a phenol formaldehyde resin. Polystyrene is a synthetic aromatic polymer made from the styrene monomer. Polythene is a thermoplastic polymer consisting of long hydrocarbon chains.

Page No 44:

Question 6:

Which of these plastics can be repeatedly heated and moulded into any desired shape?
(a) bakelite
(b) polythene
(c) formica
(d) melamine

Answer:

(b) polythene
Polythene is a thermoplastic polymer consisting of long hydrocarbon chains. Thermoplastic polymers can be repeatedly heated and moulded into any desired shape.



Page No 45:

Question 7:

Which of these can you use as a substitute for glass in windows?
(a) polythene
(b) PVC
(c) perspex
(d) teflon

Answer:

(c) perspex
Perspex is a thermoplastic. It is transparent like glass but it is much stronger. It is used as a substitute for glass in windows.

Page No 45:

Question 8:

Which of these is not a property of plastics?
(a) bad conductor of heat
(b) bad conductor of electricity
(c) inflammable
(d) soluble in water

Answer:

(d) soluble in water
Plastics are insoluble in water. That is why plastic buckets are used to store water and plastic glasses are used to drink water.

Page No 45:

Question 1:

What name is given to natural materials that are used to manufacture human-made materials?

Answer:

Natural materials that are used to manufacture human-made materials are known as raw materials.

Page No 45:

Question 2:

What is the most common source for synthetic fibres?

Answer:

The most common source for the synthetic fibres is petroleum.

Page No 45:

Question 3:

Which artificial fibre is made from wood pulp?

Answer:

Rayon is an artificial fibre that is made from wood pulp.

Page No 45:

Question 4:

Cotton and wool are natural polymers. True or false?

Answer:

True.
Natural polymers are the products of raw materials found in nature that can be extracted.
Wool is obtained from sheep and certain other animals. Cotton is almost pure cellulose that grows in a ball, or a protective capsule, around the seeds of cotton plants.

Page No 45:

Question 5:

Which synthetic fibre is commonly used to make strong ropes?

Answer:

Nylon is a synthetic fibre which is very strong, even stronger than steel wire. Therefore, it is commonly used to make strong ropes.

Page No 45:

Question 6:

Which synthetic fibre is also called artificial silk?

Answer:

Rayon, a synthetic fibre, is also called artificial silk.

Page No 45:

Question 7:

All plastics are made of long chain molecules called __________

Answer:

All plastics are made of long chain molecules called polymers.

Page No 45:

Question 8:

Name the plastic whose sheets are used for packing liquids.

Answer:

Polythene sheets are used for packing liquids.

Page No 45:

Question 9:

From which plastic material is thermocol made?

Answer:

Thermocol is made from polystyrene plastic.

Page No 45:

Question 10:

Which plastic material is used to make non-stick pans?

Answer:

Teflon is used to make non-stick pans. This is because teflon is a very slippery material. In addition to being slippery, the material also has a number of other features. It has high temperature resistance, little reaction to most chemicals and reduced stress-cracking and corrosion.

Page No 45:

Question 11:

Name one thermosetting plastic which is a good insulator and is used to make plugs and switches.

Answer:

Bakelite, a thermosetting plastic, is used to make plugs and switches. Thermosetting plastics are bad conductors of heat and electricity. They do not allow electricity to pass through, which is why they are used to make plugs and switches.

Page No 45:

Question 1:

Give two examples each of natural and synthetic fibres.

Answer:

Examples of natural fibres:
1) Cotton
2) Silk
Examples of synthetic fibres:
1) Nylon
2) Polyester

Page No 45:

Question 2:

What is a polymer?

Answer:

The word ‘polymer’ comes from two Greek words ‘poly’ meaning many and ‘mer’ meaning part or unit. When smaller units of a chemical substance are combined to form a large single unit, it is called a polymer. Examples are cellulose, polythene etc.

Page No 45:

Question 3:

Why is rayon called a regenerated fibre?

Answer:

Rayon is called a regenerated fibre because its preparation involves the chemical breakdown of cellulose using an alkaline solution. This is followed by the regeneration of solidified synthetic fibres by passing them through spinnerets.

Page No 45:

Question 4:

List two disadvantages of synthetic fibres.

Answer:

Two disadvantages of synthetic fibres are:
1) Synthetic fibres can’t absorb moisture, which makes them unsuitable during summer. They stick to the body and cause skin irritation when the body sweats during summers.
2) They are dangerous to be worn near fire or heat as they can catch fire easily.

Page No 45:

Question 5:

What is a plastic? All plastics have one common property−what is it?

Answer:

Plastic is a synthetic material made from a wide range of organic polymers such as polyethylene, PVC, nylon etc., that can be moulded into shape while soft, and then set into a rigid or slightly elastic form.
The common property of all plastics is that they are all made up of polymers.

Page No 45:

Question 6:

Why are plastic bottles commonly used to store chemicals in a chemistry laboratory?

Answer:

Plastic bottles are commonly used to store chemicals in a chemical laboratory because plastics are non-reactive. They are inert to air and water. They are non-corrosive, therefore we can store chemicals in them safely.

Page No 45:

Question 1:

List the important properties of nylon that make it a useful synthetic fibre. Give two important uses of nylon.

Answer:

Following are the properties of nylon which make it a useful synthetic fibre:
1) Nylon fibre is very strong and elastic.
2) It is light and wrinkle resistant.
3) It is easy to wash and it absorbs less water, and so it can be dried quickly.

The uses of nylon are:
1) It is used to make ropes.
2) It is useful in making garments, socks and stockings.

Page No 45:

Question 2:

Give three uses of polyester, and explain the reason for each use.

Answer:

The uses of polyester are as follows:
1) Being very strong and crease resistant, polyester is used to make pants, shirts, suits and bed sheets.
2) Because of its water-resistant properties, it is used to make jackets and garments that are used in wet and damp environments.
3) Polyesters are used to make bottles, utensils and wires as they are light weight and elastic.

Page No 45:

Question 3:

These days clothes made out of a mixture of synthetic fibres and natural fibres are more popular than those made purely out of synthetic fibres. Discuss the reasons for this.

Answer:

Clothes purely made of synthetic fibres are not comfortable in hot and humid weather as they are water resistant and do not absorb sweat from the body. They catch fire easily and stick to the body and cause severe burns and injuries.Therefore, they are not suitable in kitchen and laboratories. On the other hand, clothes spun out of fibres made by a mixture of synthetic and natural fibres do not cause such problems. Moreover, mixing synthetic fibres with natural fibres enhances their properties, such as strength, elasticity and ease of washing and ironing.

Page No 45:

Question 4:

Differentiate between thermoplastics and thermosetting plastics. Give two examples of each.

Answer:

Thermoplastics        Thermosetting plastics
1) Thermoplastics can be softened on heating again and again, therefore they can be moulded and reshaped. Thermosetting plastics cannot be softened on heating, therefore they cannot be moulded and reshaped.
2) Thermoplastics can be bent easily. Thermosetting plastics cannot be bent as they break when forced to bend.
3) Examples are polythene and polyvinyl chloride. Examples are bakelite and melamine.



Page No 46:

Question 5:

Plastics are very useful materials. Why then is there concern today about their increasing use?

Answer:

Plastics are useful but today they have become a serious global environment and health concern due to their excessive use. This is because plastics are non-biodegradable. They cannot be decomposed by the microorganisms in the soil. Inappropriate disposal of plastics is a serious problem. It chokes drains and blocks the pores of soil, which hinders the absorption of water by soil. Plastic bags contaminate food because of the poisonous dyes associated with them. Moreover, burning of plastics releases poisonous fumes, which causes air pollution. These fumes also cause cancer.

Page No 46:

Question 6:

List three steps you can take to reduce the danger that plastics pose to the environment.

Answer:

The following three steps can be taken to reduce the danger that plastics pose to the environment:
1) We can support recycling schemes.
2) We can buy products with less plastic packaging.
3) We can practise or promote proper disposal of plastics at home and its surroundings and can encourage others to do the same.

Page No 46:

Question 1:

How is rayon made? Why is it called artificial silk? List its important properties and uses.

Answer:

Rayon is regenerated cellulose, made from wood pulp by dissolving wood pulp in an alkaline solution. The thick liquid thus produced is passed through tiny holes to make fibres, which are hardened by passing them through a bath of sulphuric acid. The fibres are then spun into yarns and woven into clothes.
Rayon is called artificial silk because it is produced from naturally occurring polymers and looks like silk. It is woven like silk fibres but is man-made, unlike silk.

The important properties of  rayon fibres are:
1) They are easier to dye in various colours.
2) Clothes made from rayon are very comfortable in summer because they can absorb sweat from the body.

The uses of rayon are:
1) It is used to make curtains, table clothes, blankets, bed sheets, carpets etc.
2) It is used to make apparels such as jackets, suits, etc.

Page No 46:

Question 2:

List and explain four properties of plastics. Give one use of plastics linked to each of these properties.

Answer:

The four properties of plastics are:
1) Plastics are poor conductors of heat and electricity. That is why they are used to make handles of cooking utensils and electrical wires. Cords of electrical appliances and cables also have plastic coating.

2) Plastics are insoluble in water and that is why we use plastic buckets to store water and use plastic glasses to drink water.

3) Plastics are inert to air and water. They are non-corrosive and therefore plastic bottles are used in chemical laboratories to store chemicals.

4) Plastics easily melt on heating and therefore they can be moulded into different shapes. Hence, they are used to make things such as toys, buckets etc.

Page No 46:

Question 3:

Give the characteristic properties and important uses of the following:
(a) polythene
(b) polystyrene
(c) teflon
(d) bakelite

Answer:

(a) The properties and uses of polythene are as follows:
Properties:
1) It is water resistant.
2) It is strong but flexible and can be rolled into sheets and moulded into different shapes.

Uses:
Polythene sheets are used for the packaging of liquids such as milk. Polythene pipes are used to transport liquids such as oil and water. Polythene containers are used to store liquids.

(b) The properties and uses of polystyrene are as follows:
Properties:
1) It can be easily moulded.
2) It has poor chemical resistance.

Uses:
It is used for the packaging of delicate materials like electronic items. It is used to make thermocol. It is also used to insulate the hollow walls of the refrigerator.

(c) The properties and uses of teflon are as follows:
Properties:
1) It is slippery and is not affected by heat.
2) It does not react chemically with other substances.

Uses:
It is used as a non-stick coating on pans and other cooking utensils. It is used for making gaskets, pump packings, valves, seals etc.

(d) The properties and uses of bakelite are as follows:
Properties:
1) It is a good electrical insulator.
2) It is harder than other plastics.

Uses:
It is used to make electrical goods, combs, fountain pens, buttons, plugs and switches.

Page No 46:

Question 1:

Do you think rayon when burnt will stick to the body like other synthetic fibres?

Answer:

Synthetic fibres catch fire very easily. They melt on heating and stick to the body of the person wearing them. However, rayon is regenerated from cellulose and it doesn't melt on burning, rather it flares up like paper and smells like it.

Page No 46:

Question 2:

Burning cotton smells like burning paper, whereas burning wool smells like burning hair. Why?

Answer:

Cotton smells like burning paper because both cotton and paper are extracted from plants and constitute mainly cellulose, whereas burning wool smells like burning hair because both wool and hair are extracted from animals and both have sulphur in them.

Page No 46:

Question 3:

Which property of plastics makes them so useful but also makes them an environmental hazard?

Answer:

Plastics are non-reactive. They last much longer than any other material. They cannot be decomposed by bacteria and so are non-biodegradable in nature. These properties make plastics useful but also make them as environmental hazard.

Page No 46:

Question 4:

Clay is a 'plastic' material. Does this imply that it is a polymer?

Answer:

Clay is a 'plastic' material because we can mould it into different shapes, which is a property of plastic. But clay is not a polymer because polymers are made up of monomer units while clay is not made up of monomer units. Clay is a mixture of compounds.

Page No 46:

Question 5:

Ankit was learning how to cook. His father strictly told him not to wear nylon clothes in the kitchen. Why?

Answer:

Nylon is a synthetic fibre. Synthetic fibres catch fire easily. They are inflammable. They melt on heating and stick to the body of the person wearing them which causes severe burn injuries. Therefore, these type of clothes are not suitable in a kitchen.

Page No 46:

Question 1:

Lata always prefers to buy things from the market that use fewer plastics in packaging why does Lata do this?

Answer:

Lata always prefers to buy things from the market that use fewer plastics in packaging because of the following reasons:
1. They are non-biodegradable in nature.
2. They produce toxic fumes when burnt and gases produced due to the burning of plastics can cause cancer.
3. They harm the environment by choking the drains.
4. Recycling of plastic is more costly than its manufacturing.
 



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