NCERT Exemplar Class 8 Science Solutions Chapter 3 Synthetic Fibres and Plastics

Multiple Choice Questions 

1. Pick the synthetic fibre out of the following?  

(a) Cotton

(b) Nylon

(c) Jute

(d) Wool 

Ans: (b) Nylon

Cotton, jute, and wool are natural fibres as they are obtained from plants and animal sources. Nylon is a synthetic fibre as it is made from polymers via a chemical process.

2. Which of the following is a source of rayon?  

(a) Wool 

(b) PET 

(c) Wood pulp 

(d) Silk Solution 

Ans: (b) Wood pulp 

Rayon is made from purified cellulose and is extracted from wood pulp (usually from pine, spruce, or hemlock trees) by chemical treatment.

3. Polycot is obtained by mixing 

(a) nylon and wool 

(b) polyester and wool 

(c) nylon and cotton 

(d) polyester and cotton 

Ans: (d) Polyester and cotton 

Polycot is made by blending polyester and cotton. Polycot, or cotton-blended polyester, is made by spinning synthetic polyester fibres with natural cotton fibres.

4. Which is thermosetting plastic?  

(a) Melamine 

(b) Polythene

(c) PVC 

(d) Nylon 

Ans: (a) Melamine

Thermosetting plastics are those plastics that, once moulded, cannot be softened by heating. That means they can only be heated and shaped once. Examples are Melamine and Bakelite.

5. The material similar to silk in appearance is 

(a) Nylon

(b) Rayon

(c) Polyester

(d) Terylene 

Ans: (b) Rayon 

Rayon, generally known as artificial silk, can be dyed in a wide variety of colours. It is infused with either cotton or wool to prepare bedsheets and carpets. Rayon is less expensive than silk and can be extracted from the chemical treatment of wood pulp. Rayon is a man-made or synthetic fibre and has properties similar to those of silk.

6. The most suitable material for the preparation of handles of cooking utensils is 

(a) Polythene 

(b) PVC

(c) Nylon

(d) Bakelite 

Ans: (d) Bakelite 

Bakelite is the most suitable object to prepare the handles of cooking utensils as it does not become soft on getting heat. Bakelite mouldings are heat resistant (a poor conductor of heat) as well as scratch-resistant.

7. Which of the following is not a common property of plastics?  

(a) Non-reactive 

(b) Light in weight 

(c) Durable 

(d) Good conductor of electricity 

Ans: (d) Good conductor of electricity 

Plastics are insulators; hence they do not conduct heat or electricity. They are non-reactive. As a result, they are resistant to the attack of their surroundings. They are very light in weight. They have high durability (long life).

8. Which of the following represents the correct match for items in Column A with those in Column B. 

(a) I- (ii), II- (iii), III- (i) 

(b) I- (iii), II- (i), III- (ii) 

(c) I- (ii), II- (i), III- (iii) 

(d) I- (iii), II- (ii), III- (i) 

Ans: (c) I-(ii), II-(i), III-(iii) 

9. Which of the following groups contain all synthetic substances?  

(a) Nylon, Terylene, Wool 

(b) Cotton, Polycot, Rayon 

(c) PVC, Polythene, Bakelite 

(d)  Acrylic, Silk, Wool 

Ans: (c) PVC, Polythene, Bakelite 

PVC, or Poly Vinyl Chloride, is a polymer which is made from the polymerisation of vinyl chloride. PVC is tough, lightweight and abrasion-resistant.

One of the most widely used plastics is polyethylene, commonly known as polythene or polyethene. This is often used for the production of plastic bags, plastic films, bottles, and containers.

Bakelite is a thermosetting plastic made from synthetic components. It is a phenol-formaldehyde resin. They are heat and scratch-resistant. 

10. The material which is commonly used for making kitchen containers is 

(a) PVC

(b) Acrylic 

(c) Teflon 

(d) PET 

Ans: (d) PET

PET, also known as Polyethylene terephthalate, is very light-weight, strong, durable, and non-reactive, that's why it is used to make kitchen containers.

VERY SHORT ANSWER QUESTIONS 

11. Cotton is a natural polymer. What is its chemical name?

Ans: Cellulose is the chemical name of cotton which is a natural fibre obtained from plants. 

12. A synthetic fibre that looks like silk is obtained by the chemical treatment of wood pulp. It is, therefore, known as artificial silk. What is its common name?  

Ans: Rayon, generally known as artificial silk, can be dyed in a wide variety of colours. It is infused with either cotton or wool to prepare bedsheets and carpets. Rayon is less expensive than silk and can be extracted from the chemical treatment of wood pulp. Rayon is a man-made or synthetic fibre and has properties similar to those of silk. 

13. Terry cot is made by mixing two types of fibres. Write names of the fibres.  

Ans: Terrycot is prepared by mixing terylene (35%), and cotton (65%). Terrycot fabric is convenient and comfortable to wear as compared to Terylene, which is a popular polyester fibre. 

14. Plastic articles are available in all possible shapes and sizes. Can you tell why?  

Ans: Plastics are easily moldable and, thus, plastic articles are available in all shapes and sizes. Plastics can be transformed into objects of different varieties because plastic is considered to be a different material as it becomes soft on heating and becomes hard on cooling at lower temperatures. Plastics have a very low melting point. After melting, they are put in moulds and moulded into different shapes and sizes.

15. Plastic is used for making a large variety of articles of daily use and these articles are very attractive. But it is advised to avoid the use of plastic as far as possible. Why? 

Ans: Plastic is widely used for making a large variety of articles used on a daily basis because of its low cost, versatility, and durability. Plastic is a non-biodegradable substance. That is why it is causing havoc on the environment. Chemicals used in the manufacture of plastics are absorbed by humans. Some of these substances have been discovered to change hormones or have other possible health consequences in humans. Eating meals from plastic containers have been linked to cancer. Plastic production and recycling both emit harmful gases and residues that pollute the air, water, and land. That is why it is advised to avoid the use of plastic as much as possible.

16. Why is it not advisable to burn plastic and synthetic fabrics?

Ans: Burning of plastic and synthetic fibres produces lots of poisonous gases (dioxins, furans, mercury and polychlorinated biphenyls) into the atmosphere, and poses a threat to vegetation, and human and animal health. As a result, burning plastic and synthetic fibres are not recommended.

17. Select the articles from the following list which are biodegradable.  

(a) paper

(b) woollen clothes 

(c) wood

(d) aluminium can 

(e) plastic bag

(f) peels of vegetables 

Ans: A biodegradable material is one that can be decomposed by bacteria or other natural organisms without polluting the environment. A non-biodegradable material is a substance that cannot be broken down by natural organisms and is, therefore, a source of pollution. The list of biodegradable articles is mentioned below

(a) Paper 

(b) Wooden clothes 

(c) Wood 

(f) Peels of vegetables

18. A bucket made of plastic does not rust like a bucket made of iron.  Why?  

Ans: A bucket made of plastic does not rust after being left open to air and water because plastic is non-reactive and it does not react with it. The bucket made of iron reacts with air and water and corroded to form iron oxides also known as rust 

SHORT ANSWER QUESTIONS 

19. Rohit took with him some nylon ropes when he was going for rock climbing. Can you tell why he selected nylon ropes instead of ropes made of cotton or jute?  

Ans:  Rope made of nylon is stronger, more flexible, light in weight, and elastic than ropes made of jute or cotton. Even nylon ropes are stronger than steel ropes of the same thickness. Thus, nylon is used to make ropes, especially when it comes to mountain climbing. Jute ropes are comparatively weaker, and using them to make ropes for mountaineering can be risky for climbers. That's why Rohit took nylon rope with him when he was going for rock climbing.

20. A lady went to the market to buy a blanket.  The shopkeeper showed her blankets made of acrylic fibres as well as made of wool. She preferred to buy an acrylic blanket. Can you guess why?  

Ans: Acrylic blankets are manufactured using acrylic yarn, which is a petroleum-based product that takes a long time to degrade. Acrylic blankets are light in weight, inexpensive, durable, and also available in a variety of colours and designs. They are easily washable. Another benefit of the acrylic blanket is that, since it is a synthetic fibre, it is impossible for moth larvae to digest it. 

21. PVC (polyvinyl chloride) is a thermoplastic and is used for making toys, chappals, etc. Bakelite is a thermosetting plastic and is used for making electrical switches, handles of various utensils, etc. Can you write the major difference between these two types of plastics?  

Ans: The differences between thermoplastic and thermosetting plastic are: 

22. Fill in the blanks:

(i) A polymer is a chain of many small units joined together which are called_______. 

Ans: Monomers

(ii) The synthetic fibres are also known as_____ fibres.  

Ans: Man-made

(iii) The first fully synthetic fiber was _______. 

Ans: Nylon

(iv) A fiber similar to wool is_______.

Ans: Acrylic

(v) A plastic used for making crockery is _______.

Ans: Melamine

23. Match items in List A with the items of list B. 

Ans: 

24. Unscramble the jumbled words given below, related to synthetic materials.  

(a) anory 

Ans: Rayon

(b) lopmery

Ans: Polymer 

(c) relyteen 

Ans: Terylene

(d) laspict

Ans: plastic

(e) yespolter

Ans: Polyester 

(f) felton

Ans: Teflon 

LONG ANSWER QUESTIONS

25. Indicate whether the following statements are True or False. Also, write the false statements in their correct form.  

(i) The fabric terry wool is obtained by mixing terylene and wool.  

Ans: True

(ii) Synthetic fibres do not melt on heating.

Ans: False, because synthetic fibres melt on heating.

(iii) It is risky to wear synthetic clothes while working in the kitchen.

Ans: True 

(iv) Most of the plastics are biodegradable.

Ans: False, most of the plastics are non-biodegradable.

26. Write the importance of synthetic polymers in our life.  

Ans: The importance of synthetic polymers in our lives is as follows: 

1. Nylon is very strong, elastic, flexible, and light in weight and can be used for making hill climbing ropes, fishing ropes, parachutes, and raincoats. 

2. Acrylic, which is a petroleum-based product, is light in weight, inexpensive, durable, and also available in a variety of colours and designs. Sweaters, blankets, tracksuits, gloves, boots, etc. are made from acrylic. 

3. Terylene is a synthetic polyester fibre obtained from petroleum that is manufactured by polymerizing ethylene glycol and terephthalic acid. It is mainly used in making plastic bottles, sheets, ropes, nets, sails, tapestries, raincoats, fleece jackets, and dress materials. 

4. Plastic containers are non-reactive, strong, durable, and light in weight. That is why they are used to store pickles, dry food, milk, water, and many other items.  

27. Despite being very useful it is advised to restrict the use of plastic. Why is it so? Can you suggest some methods to limit its consumption?  

Ans: Plastics are non-biodegradable and are restricted in use. Plastics do not decompose in the atmosphere. Plastics, if eaten mistakenly by any animal, may damage the animal's health. The burning of plastic may release lots of poisonous gases (dioxins, furans, mercury, and polychlorinated biphenyls) into the atmosphere, posing a threat to vegetation and human and animal health. 

Some methods to limit plastic consumption are: -

1. Reducing the use of plastics. Paper and jute bags should be used instead of plastic bags whenever possible. 

2. Reusing it for another purpose reduces its consumption.

3. Recycling of plastic necessitates the collection, sorting, chopping, melting, and remoulding of plastic.  

4. Do not burn the plastic since it releases carbon monoxide, a carcinogenic gas. 

28. Write an activity to show that synthetic fibres are stronger than the cotton fibres. 

Ans: 

Activity- Take two threads, cotton and nylon, of the same length and thickness. Hang the cotton thread by attaching it to the clamp as shown in the illustration. Now, add weight to it and keep adding until the thread breaks. Make a list of all the weights you've collected and add them all up. Repeat this process with nylon thread too.

Conclusion- You will see that nylon thread suffered more damage than cotton thread. It is because nylon thread is much stronger than cotton thread.

29. Complete the crossword given below with the help of clues.  

Across 

1. Substance used as synthetic wool (7) 

Ans: Acrylic 

2. A plastic used for making containers and carry bags (9) 

Ans: Polyethylene 

3. Substance made up of large number of smaller molecules (7)

Ans: Polymer 

4. Another name for this compound is artificial silk (5)

Ans: Rayon 

Down 

5. A type of fibre obtained naturally from cocoon (4)

Ans: Silk

6. A synthetic fibre classified as polyester (8) 

Ans: Terylene 

7. A polymer used for making rope (5)

Ans: Nylon

Class 8 Science Solutions Chapter 3 Synthetic Fibres and Plastics

Fibers

Fibers are thread-like structures with thin, long, and flexible strands that can be broadly defined. Animals and plants are the two primary suppliers of fibers. The fibers are spun into yarns, which are subsequently woven into the finest textiles. A single long fiber may provide yarn for a variety of fabrics on average.

Polymers

A polymer, also known as a macromolecule, is a big molecule made up of numerous subunits. Polymer is a Greek word that means many components.' Polymers may be found in almost every environment, from our DNA strand, which is a naturally occurring biopolymer, to polypropylene, which is utilized as a plastic all over the world. Polymers can be derived from natural sources in plants and animals (natural polymers) or artificially created (synthetic polymers). Polymers have a wide range of physical and chemical properties that make them useful in everyday life.

Synthetic

Synthetic fiber is an artificial fiber whose majority comes from petroleum-based materials known as petrochemicals. Fibers are used to make all textiles, and they can come from natural or artificial sources. Basically, they're made up of tiny units, or polymers, consisting of many monomers that repeat. Every year, millions of tonnes of these fibers are manufactured all over the world.

Natural Fiber

The phrase "natural fiber" refers to fibers acquired from (or generated by) animals and plants. They consist of microscopic units called polymers, which are built up from repeating monomers. Matting various layers of natural fibers into sheets can make paper and felt (a type of textile material). Most natural fibers are well-known for their ability to absorb sweat and other liquids. Natural fibers may be used to create a broad range of textures (either individually or through two or more natural fibers). Cotton fibers (natural fibers generated from the cotton plant) are used to create cotton garments known for their low weight and delicate feel. Cotton fiber also has the benefit of being weaved into clothes of various sizes and colors. Apparel constructed of natural fibers is commonly referred to as "synthetic fiber" clothing.

Fibres Obtained From Silkworm

• Silk

Silk is a natural protein fiber that is utilized in the textile industry. Silkworm produces one of the most critical animal fibers. Silkworms of various species create various sorts of silk. The luster and texture can be used to distinguish it. Kosa, Tassar, and Mooga are a few instances. Silkmoths of several species create them. Mulberry silk moths are one of the most prevalent varieties.

• Rayon

The cellulose molecule is chemically converted into rayon by converting it into a soluble molecule. Natural fibers such as wood pulp are used to manufacture rayon, a manufactured fabric. As a result of its chemical treatment, rayon can be a strong fabric. Rayon is a material that is less expensive than silk but can be weaved like silk.

Synthetic Fibres

• Nylon

Nylon is a manufactured fiber that is made from coal, water, and air. Nylon was the first synthetic fiber discovered. It has the characteristics of being light, robust, and elastic. Nylon is used to make stockings, sleeping bags, ropes, tents, car seat belts, and curtains, among other things.

• Polyesters

Polyesters are almost like a polymer with the main chain made up of esters. The clothing contains a lot of these polymers. In reality, polyester fibers are frequently used with natural fibers to provide clothes with certain qualities.

• Acrylic

Acrylic is a synthetic fiber that probably looks like wool. Wool from natural sources is relatively costly. However, synthetic clothing is reasonably inexpensive. Synthetic fibers are more durable and inexpensive than natural fibers, making them more popular.

Plastic and the Environment

• Plastic

Plastic is a polymer, just like synthetic fibers. All polymers have different arrangements of units. In some cases, they are linear, and in others, they are cross-linked. Recycling, repurposing, coloring, melting, rolling, and wired plastic is possible. This explains the vast array of uses for the material. 

• Thermoplastics

Thermoplastics are polymers that distort easily when heated and maybe bend with ease. Polythene and PVC, for example.

• Thermosetting Plastics

The heating process will not soften plastic once it has been molded. For example, bakelite and melamine.

Classification of Materials

• Biodegradable

Biodegradable is used to describe materials that disintegrate naturally (for example, by bacterial activity).

• Non-biodegradable

Non-biodegradable materials are those that are not easily degraded by natural processes.