Lakhmir Singh & Manjit Kaur: Synthetic Fibers And Plastics- 3 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.51. 
(A) What is rayon? How is rayon made?

Rayon is the man-made fibre prepared from the natural materials. It is the man-made fibre which is regarded as artificial silk. It is obtained by the chemical treatment of wood pulp or cellulose. Although rayon is obtained from natural source, wood pulp, yet it is a manmade fibre. Its fibres can also be woven like those of natural fibres. It is cheaper than silk but can be woven like silk fibres. It can also be dyed in a variety of colours.

(B) Give any two uses of rayon.

Rayon can be used in the following ways:

• It can be mixed with cotton to make bed sheets.
• It can also be mixed with wool to make carpets.
• It is also used in textile industry to make textiles.

Q.52. 
(A) What are synthetic fibres? Name any two synthetic fibres.

Synthetic fibres are man-made fibres which are made up of small units which are joined together. These units are made of chemical substances. Such small units combine to form a large single unit called a polymer. Hence, a polymer is made of many repeating units. Polymers also occur in nature.

Example: Rayon and Nylon are synthetic fibres. Rayon is obtained by the chemical treatment of wood pulp or cellulose. Nylon is the first fully synthetic fibre. It was prepared from coal, water and air.

(B) Why have synthetic fibres become more popular than natural fibres?

Synthetic fibres become more popular than natural fibres because they are cheaper than natural fibres. The raw materials for synthetic fibres are mainly petrochemicals such as coal. Hence, the manufacturing of synthetic fibres helps in the conservation of forests. Synthetic fibres are used in the manufacture of a variety of household articles such as ropes, buckets, furniture, containers, etc. to highly specialized uses in aircrafts, ships, space crafts, healthcare, etc.

Q.53.
(A) What are thermoplastics? Give two examples of thermoplastics.

Plastic is a polymer like a synthetic fibre. The arrangement of units in a plastic can be linear or cross-linked. The plastics which gets deformed easily on heating and can be bent easily are called thermoplastics. For example, polythene and PVC are thermoplastics. These are used in the manufacturing of toys, combs and different types of containers.

(B) What are thermosetting plastics? Give two examples of thermosetting plastics.

Thermosetting plastics: The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics. For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. It is used to make floor tiles, kitchenware and fire resistant fabrics. It is used to make electrical switches and handles of utensils.

Q.54. Explain why, thermoplastics become soft on heating but thermosetting plastics do not become soft on heating. Draw labelled diagrams to illustrate your answer.

Thermoplastic materials are made of polymers which are linked by intermolecular forces, forming linear or branched structures. On the other hand, thermosetting plastics are those materials that are made by polymers joined together by chemical bonds, having a highly-crosslinked polymer structure. In case of thermoplastics, the shape hardens when it is cooled, but can be reshaped when heated up again. Polythene is a thermoplastic polymer. Its tangled polymer chains can uncoil and slide past each other, making it a flexible material. On the other hand, Thermosetting polymers, once moulded, cannot be softened when heated. They cannot be reshaped. Vulcanised rubber is a thermosetting polymer which is used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily.

Lakhmir Singh Science Class 8 Solutions Chapter 3 Synthetic Fibers and Plastics 1

Q.55. What is meant by biodegradable and non-biodegradable materials? Give examples of two biodegradable and two non-biodegradable materials.

The materials which gets decomposed through natural processes, such as by the action of microorganisms are called biodegradable materials. For example, peels of vegetables and fruits, cotton clothes, wood and paper are biodegradable substances. These materials are easily decomposed by microorganisms. Temperature and sunlight may also play roles in the decomposition of biodegradable plastics and other materials.
The materials which are not easily decomposed by natural processes are called non- biodegradable materials. For example, tin, aluminium and other metal cans and plastics are non-biodegradable materials. Plastics can take several years to decompose. These materials are not environmental friendly and cause environmental pollution.

Q.56. Rayon is different from truly synthetic fibres because:
(a) it has a silk-like appearance
(b) it is obtained from wood pulp
(c) its fibres can be woven like those of natural fibres.
(d) it can be dyed in wide variety of colours.

Correct Answer is Option (b)

Rayon is the man-made fibre which is regarded as artificial silk. It is obtained by the chemical treatment of wood pulp or cellulose.

Q.57. The synthetic material which can be used for marking fabrics as well as shatterproof bottles and jars is:
(a) nylon
(b) rayon
(c) polyester
(d) acrylic

Correct Answer is Option (c)

Polyester is the synthetic fibre which contains the organic group similar-to those which give fruits their sweet smell. PET is a very familiar form of polyester. It is used for making bottles and utensils which is replacing materials like glass.

Q.58. Which of the following has cross-linked polymer chains?
(a) bakelite
(b) polyester
(c) PVC
(d) nylon

Correct Answer is Option (a)

Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils.

Q.59. The man-made fibre made from the cellulose polymer is:
(a) nylon
(b) acrylic
(c) rayon
(d) polyester

Correct Answer is Option (c)

Rayon is obtained by the chemical treatment of wood pulp or cellulose. It is the man-made fibre which is regarded as artificial silk.

Q.60. Which of the following is not a thermoplastic polymer?
(a) polyester
(b) melamine
(c) nylon
(d) polyvinyl chloride

Correct Answer is Option (b)
The plastics which gets deformed easily on heating and can be bent easily are called thermoplastics. For example, polythene and PVC are thermoplastics.

Q.61. The synthetic polymer which can be used as a substitute for wool for making sweaters and shawls, etc. is:
(a) nylon
(b) polyester
(c) terylene
(d) acrylic

Correct Answer is Option (d)
Acrylic is a synthetic fibre which appears to resemble wool. It is flexible, resistant to moth, oil and chemicals. It is used for making sweaters and tracksuits and also for the linings of boots and gloves.

Q.62. Which of the following is not a synthetic fibre?
(a) nylon
(b) flax
(c) acrylic
(d) polyester

Correct Answer is Option (b)
Flax is a blue-flowered herbaceous plant that is cultivated for its seed and for textile fiber made from its stalks.

Q.63. The synthetic fibre which contains the group similar to those which give fruits their ‘sweet smell’ is:
(a) nylon
(b) acrylic
(c) terylene
(d) rayon

Correct Answer is Option (c)
Polyester is the synthetic fibre which contains the organic group similar-to those which give fruits their sweet smell. Terylene is a kind of a polyester.

Q.64. The man-made fibre which contains identical to:
(a) wool
(b) silk
(c) jute
(d) cotton

Correct Answer is Option (d)
Cotton is a natural fibre.

Q.65. One of the following man-made fibre is not prepared from raw materials obtained from petrochemicals. This one is:
(a) polyester
(b) nylon
(c) rayon
(d) acrylic

Correct Answer is Option (c)
Rayon is obtained by the chemical treatment of wood pulp or cellulose.

Q.66. Which of the following plastics do not have cross-links between their polymer chains
(i) Nylon
(ii) Nekamine
(iii) Terylene
(iv) Bakelite
(a) i and ii
(b) ii and iii
(c) i and iii
(d) iii and iv

Correct Answer is Option (c)
Nylon and Terylene are thermoplastic polymers. They do not have cross-links between their polymer chains.

Q.67. The clothes of a person working in the kitchen catch fire accidently causing severe burns. The person is most likely wearing clothes made of:
(a) flax
(b) rayon
(c) terylene
(d) cotton

Correct Answer is Option (c)
Terylene is a synthetic fibre. If the clothes made of synthetic fibres catch fire, it can be very dangerous. The fabric will melt and can stick to the body of the person wearing it causing severe burns.

Q.68. The plastic which is coated on the uniforms of firemen to make them fire-resistant is:
(a) Bakelite
(b) polythene
(c) Teflon
(d)  melamine

Correct Answer is Option (d)

Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. It is used to make floor tiles, kitchenware and fire resistant fabrics.

Q.69. Which of the following is a man-made fibre prepared from wood-pulp?
(a) flax
(b) nylon
(c) acrylic
(d) rayon

Correct Answer is Option (d)

Rayon is obtained by the chemical treatment of wood pulp or cellulose. It is the man-made fibre which is regarded as artificial silk.

Q.70. The manufacture of one of the following artificial fibres contributes to deforestation this fibre is :
(a) nylon
(b) rayon
(c) terylene
(d) acrylic

Correct Answer is Option (b)
Rayon is obtained by the chemical treatment of wood pulp or cellulose causing deforestation.

Q.71. The non-stick coating on frying pans is that of a plastic called:
(a) polyvinyl chloride
(b) melamine
(c) bakelite
(d) Teflon

Correct Answer is Option (d)
Teflon is a special plastic on which oil and water do not stick. It is used for nonstick coating on cook wares.

Q.72. Which of the following plastics is used for making electric switches?
(a) Teflon
(b) melamine
(c) PET
(d) Bakelite

Correct Answer is Option (d)
Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils.

Q.73. Which of the following are thermosetting polymers?
(i) Melamine
(ii) Terylene
(iii) Polythene
(iv) Bakelite
(a) i and ii
(b) ii and iii
(c) i and iv
(d) ii and iv

Correct Answer is Option (c)
Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils. Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. It is used to make floor tiles, kitchenware and fire resistant fabrics.

Q.74. The similarity between artificial silk and cotton is that:
(a) both are non-biodegradable
(b) both melt on heating
(c) both are amide polymers
(d) both are cellulose polymers

Correct Answer is Option (d)
Rayon is obtained by the chemical treatment of wood pulp or cellulose. It is the man-made fibre which is regarded as artificial silk.

Q.75. Which of the following plastic objects can be recycled?
(i) Electric socket
(ii) Polythene bag
(iii) PVC pipe
(iv) Ashtray
(a) i and ii
(b) ii and iii
(c) i and iv
(d) iii and iv

Correct Answer is Option (b)
Polythene bag and PVC pipe are the thermoplastics which can be recycled.

Q.76. Match the terms of column A correctly with the phrases given in column B:
Column A
(i) Polyester
(ii) Teflon
(iii) Rayon
(iv) Nylon
Column B
(a) Prepared by using wood pulp
(b) Used for making parachutes
(c) Used to make non- stick cookware
(d) Fabrics do not wrinkle easily

(i) Polyester – (d) Fabrics do not wrinkle easily
Fabrics made from polyester does not get wrinkled easily. It remains crisp and easy to wash.
Hence, it is suitable for making dress material.
(ii) Teflon – (c) Used to make non- stick cookware
Teflon is a special plastic on which oil and water do not stick. It is used for nonstick coating on cook wares.
(iii) Rayon – (a) Prepared by using wood pulp
Rayon is obtained by the chemical treatment of wood pulp or cellulose. It is the man-made fibre which is regarded as artificial silk.
(iv) Nylon – (b) Used for making parachutes
Nylon is the first fully synthetic fibre. It was prepared from coal, water and air. It is used for making parachutes and rock climbing ropes.

Q.77. Which plastic is used:
(a) for making uniforms of fire-men fire resistant?
(b) for giving non-stick coating on frying pans?
(c) for making handles of frying pans?
(d) for making insulation of electric wires?
(e) for making electric switches?
(f) for making flexible water bottles?

(a) Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. It is used to make floor tiles, kitchenware and fire resistant fabrics. It is also used for making uniforms of fire-men.
(b) Teflon is used for giving non-stick coating on frying pans. It is a special plastic on which oil and water do not stick. It is used for nonstick coating on cook wares.
(c) Bakelite is used for making handles of frying pans. Frying pan handles are made with thermosetting plastics which are resistant to fire and can tolerate heat better than other plastics. For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity.
(d) PVC (Polyvinyl chloride) is used for making wire insulation.
(e) Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils.
(f) PET is used for making flexible water bottles. It is a very familiar form of polyester. It is used for making bottles and utensils which is replacing materials like glass.

Q.78. Which of the following articles made of plastics ‘can be recycled’ and which cannot be recycled’ ? give reasons for your choice?
Telephone instruments, plastic toys, cooker handles, plastic covering on electrical wires, electric switches, ballpoint pens, carry bags, plastic bottles, plastic chairs

PVC (Polyvinyl chloride) bags, Plastic bottles and Plastic chairs are made of thermoplastics. These articles can be recycled. Thermoplastic materials are made of polymers which are linked by intermolecular forces, forming linear or branched structures. In case of thermoplastics, the shape hardens when it is cooled, but can be reshaped when heated up again. Polythene is a thermoplastic polymer. Its tangled polymer chains can uncoil and slide past each other, making it a flexible material.
Telephone instruments, Cooker handles, Electric switches and Ball point pens are made of Thermosetting plastics. Thermosetting plastics are those materials that are made by polymers joined together by chemical bonds, having a highly-crosslinked polymer structure. Thermosetting polymers, once moulded, cannot be softened when heated. They cannot be reshaped.

Q.79. Out of the following materials:
cotton, nylon, terylene, wool, Pet, acrylic
(a) which materials are polyesters?
(b) which materials is a polyamide?
(c) which material is used as a substitute for wool?
(d) which material is used as a substitute for glass?

(a) Terylene and PET are polyesters. Polyester is the synthetic fibre which contains the organic group similar-to those which give fruits their sweet smell. PET is a very familiar form of polyester. It is used for making bottles and utensils which is replacing materials like glass.
(b) Nylon is a polyamide. Nylon is the first fully synthetic fibre. It was prepared from coal, water and air. It is used for making parachutes and rock climbing ropes.
(c) Acrylic is used as a substitute for wool. It is a synthetic fibre which appears to resemble wool. It is flexible, resistant to moth, oil and chemicals. The clothes made from acrylic are relatively cheap and are available in a variety of colours.
(d) PET is a material used as a substitute for glass. It is a form of polyester. Polyester is the synthetic fibre which is made up of repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell. PET is used for making bottles, utensils, films and wires.

Q.80. The synthetic fibre A is chemically a polyamide whereas the synthetic fibre B contains a large number of ester groups. another synthetic fibre C is made of a polymer D which consists of a number of glucose units joined one after the other.
(a) Which fibre could be (i) terylene (ii) rayon and nylon?
(b) Name the polymer D.
(c) Which fibre (A, B or C) is prepared from a natural raw material?
(d) Which fibre (A, B or C) contains the same type of groups as those in a PET jar?

(a) Fibre could be

• terylene could be the synthetic fibre B which contains a large number of ester groups.
• Rayon could be the synthetic fibre C which is made of polymer D containing glucose.
• Nylon could be the fibre A which is chemically a polyamide is nylon. It is the first fully synthetic fibre. It was prepared from coal, water and air.

(b) Polymer D is Cellulose. A polymer is made of many repeating units. Polymers also occur in nature. For example, cotton is a natural polymer which is made from the cellulose. Cellulose is made up of a large number of glucose units.
(c) Fibre C is prepared from a natural raw material. Fibre C is Rayon. Rayon is obtained by the chemical treatment of wood pulp or cellulose. It is the man-made fibre which is regarded as artificial silk.
(d) The fibre B which is terylene contains the same type of groups as those in a PET jar. Terylene and PET are both polyesters.