Synthetic Fibers And Plastics: NCERT Class VIII, Science – Chapter 3

Synthetic Fiber

Synthetic fibers are made of very large units called ‘polymer’. The synthetic fibers are obtained by chemical processing of petrochemicals. Different types of synthetic fibers are like – rayon, nylon, polyester etc.

Polymer

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

Biodegradable materials

A material which gets decomposed through natural processes such as, action by bacteria are called ‘biodegradable’ materials. Examples – paper, wood, vegetables etc.

NCERT Textbook Exercise Questions (Important only)

Q.1: Explain why some fibers are called synthetic?

Ans: Some fibers are called synthetic fibers because they are man-made. These fibers made by the combination of different types of chemicals in industries and their nature are also different in respect of natural fiber.

Q.3: Fill in the blank with appropriate words:

i. Synthetic fibers are also called ______ or ______ fibers.

ii. Synthetic fibers are synthesized from raw material called _____.

iii. Like synthetic fibers, plastic is also a ______.

Ans: i. man-made or natural fibers, ii. petrochemicals iii. polymer.

Q.4: Give examples which indicate that nylon fibers are very strong.

Ans: Nylon fibers are very strong, thus they are used to prepare ropes for mountaineering. They are also used to prepare parachutes.

Q.5: Explain why plastic containers are favoured for storing food.

Ans: Advantages of storing foods in plastic containers are:

1) The plastics do not react with the food stored in them.

2) The plastics are light weight and are strong.

3) They are easy to handle and safe.

4) They are cheap (affordable) and ductile.

Q.6: Explain the difference between the thermoplastic and thermosetting plastics.

Ans: Difference between thermoplastic and thermosetting plastics is as follows:

Thermoplastic Thermosetting Plastics

1. Thermoplastic is a soft material

2. It can be bent easily

3. It can be melted on heating

4. It can be re-shaped

5. These are good conductors of heat

6. Examples: Polythene, PVC 1. Thermosetting plastic is a hard material

2. It can’t be bent

3. It can’t be melted on heating

4. It can’t be re-shaped

5. These are bad conductors of heat

6. Examples: Bakelite, Melamine

Q.7: Explain why the following are made of thermosetting plastics:

a. Saucepan handles

b. Electric plugs / switches / plug boards.

Ans: a. The handles of saucepans are made of thermosetting plastics because it is a bad conductor of heat and so, do not get heated up while cooking. So it is easier to handle the utensil while cooking. Moreover it does not get softened due to heat.

b. Electrical plugs, switches and plug-boards are made up of thermosetting plastics because it is a bad conductor of electricity. It does not allow the electric current to pass through it, thus safe in using in electric appliances.

Q.8: Categorize the materials of the following products into ‘can be recycled’ and ‘can not be recycled’:

Telephone Instruments, Toys, Cooker handles, Carry bags, Ball point pens, Plastic bowls, Electric wire covering, Plastic chairs, Electrical switches.

Ans: Can be recycled: Toys, carry bags, plastic bowls, ball point pen, plastic chair, electric wire covering. Can’t be recycled: Cooker handles, electrical switches, telephone instruments.

Q.9: Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made of synthetic material? Advise Rana giving your reasons.

Ans: Cotton clothes are preferred to synthetic clothes in summer because cotton is a bad conductor of heat. It does not allow the outer heat to enter in our body, thus protects our body from heat. Also it has more capacity to hold moisture than the synthetic clothes. So, it retains the sweat of the body and keeps it cool.

So Rana should buy shirts made up of cotton.

Q.10: Give examples to show that plastics are noncorrosive in nature.

Ans: Plastics are noncorrosive in nature because it is a nonreactive substance. It does not react with air, water, minerals and other chemicals. So in present days most of the containers, utensils and laboratory equipments are made with plastics to store food, chemicals etc.

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

Ans: For the handles and bristles of toothbrush we can not choose same type of plastics because bristles are used to clean our teeth and gum. So it must be a type of thermoplastic that is nylon but handles of toothbrush must be strong and tough so that it can give some grip and resist our efforts on it. So it should a type of thermosetting plastic.

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

Ans: Plastics are non-biodegradable materials. They take several years to decompose. It is not environment friendly and causes environment pollution. Also burning process of plastics is quite slow. In the process of burning it releases lots of poisonous gas into the atmosphere causing air pollution. Some plastics can’t be recycled and so, it is very difficult to finally dispose off such materials. Polythene bags, carelessly thrown in an eating garbage can cause death for the animals like – cows, dogs etc or sometimes even become a cause for clogging of the drains.

The only solution to get rid of these problems is to reduce the use of plastics. There lies the justification for saying that ‘Avoid plastics as far as possible’.

Q.13: Match the terms of column I correctly with the phrases given in column II:

Column I Column II

(i) Polyester

(ii) Teflon

(iii) Rayon

(iv) Nylon a. Prepared by using wood pulp

b. Used for making parachutes and stockings

c. Used to make non-stick cook wares

d. Fabrics do not wrinkle easily

Ans: (i) – d (ii) – c (iii) – a (iv) – b

Q.14: ‘Manufacturing synthetic fibers is actually helping conservation of forests’. Comment.

Ans: The natural fibers are obtained from plants and animals, whereas the synthetic fibers are obtained by chemical processing of petrochemicals. Unlike natural fibers, manufacturing of synthetic fibers do not require to cut trees or hunting of any animal. In this way manufacturing synthetic fibers is actually helping conservation forests.

Short type Questions with their Answers

Q.1: Why rayon is completely synthetic fiber?

Ans: Rayon is not completely synthetic fiber because it is not completely made of synthetic materials. It uses tree pulp as the raw material.

Q.2: What is PET?

Ans: PET is a form of polyester. It is synthetic material. It is mainly used to make bottles, utensils, films, wires and many other useful products. The most common and visible usage being PET jars in our kitchens.

Long type Questions with their Answers

Q.1: Name different artificial fibers and write their uses.

Ans: Following are the main synthetic fibers:

• Rayon – It’s also called the artificial silk as it has great luster and is light in weight. It is obtained by chemical treatment of wood pulp. It can be woven like silk and dyed in different colours. It’s used as dress material. Mixed with cotton, it is used to make curtains, bed-sheets etc. It’s used with wool to make beautiful carpets.

• Nylon – It’s the strongest, 100% manmade fiber. It’s made by coal, water and air. It’s elastic in nature and light in weight. It is lustrous and thus ideal for making dresses. Nylon is also used to make stockings, seat-belts, ropes, tents, toothbrushes, sleeping bags, curtains, parachutes etc.

• Polyester – It is made up of multiple units of ‘esters’. The clothing made of this fiber does not get wrinkled easily. It’s always crisp and easily washable. PET is also derived from polyester which in turn is used to make containers, utensils, films, wires etc.

• Acrylic – Acrylic is like wool and is used to make sweaters and suit lengths.

Q.2: Explain uses of Melamine and Bakelite.

Ans: Uses of Melamine – Melamine is a kind of thermosetting plastic which has great capacity to tolerate heat. It does not allow the heat to pass through easily. Melamine being a fire-resistant material has many other uses like in making kitchenware and handles of the cooking ware so that they do not heat up and remain easy to handle while cooking. It is also used in preparing fire resistant fabrics.

Uses of Bakelite – Bakelite is a poor conductor of electricity and does not allow the electric current to pass through it. Therefore, it’s used to make electric plugs and switches. Because of its heat resistant character it is used to make handles of utensils.

Q.3: Write advantages of disadvantages of synthetic fibers.

Ans: Advantages of synthetic fibers:

1) Most of the synthetic fibers are wrinkle resistant. So it is convenient to wash and wear.

2) Synthetic fibers are strong so they can take up heavy loads easily. They have got high tensile strength, which enables them to carry weights.

3) They have great elasticity and so can be easily stretched.

4) Synthetic fibers are generally soft, because of which they used to make variety of clothes and clothing materials.

Disadvantages of synthetic fibers:

1) Synthetic fibers can’t absorb moisture. This makes them unsuitable during summer. When our body sweats this make body sticky and skin irritating.

2) They are dangerous to be worn near fire or heat, as they can easily catch fire.

3) They are difficult to iron (press) as they melt very easily.

Q.4: How disposal of plastic is a problem? Explain. or Why the wastage of plastics is considered against eco-friendly?

Ans: There are several reasons for which the wastage of plastics is considered not eco-friendly (environment friendly). First of all, the plastics are non-biodegradable in nature and take several years to degenerate. Some plastics which can not be recycled are a great problem to finally dispose them off. The burning of plastics is also a very slow process during which they release a lot of poisonous gases to the environment causing air-pollution. If thrown carelessly in an eating garbage, they may cause death for some animals like – cows, dogs etc. The polybags, plastic wrappers etc carelessly thrown here and there are responsible for clogging of drains. Being non-degradable, sometimes such disposed plastic wastes get buried into the soil causing soil pollution and decreasing soil fertility. Because of all these reasons the disposal of plastic remains a genuine problem and wastage of plastics is also considered as against environment friendly.

Objective type Questions with their Answers

Q.1: Fill in the blanks:

a. The fiber we get from plants and animals `is called _______.

b. The fiber we obtain from chemicals is called _______.

c. The chemicals of petroleum origin used to form synthetic fiber are called _______.

d. Synthetic substances apart from fibers are _______.

e. Plastics which can be bent and moulded are called _______.

f. ______ is used to make the handles of cookware because it is _______ to heat.

g. Switch board and electric plugs are made of _______.

h. ______ is the most expensive natural fiber.

i. Cotton is the polymer of _____.

j. We should avoid using ________ carry bags.

Ans: a – natural fiber, b – artificial / synthetic fiber, c – petrochemicals, d – plastics, e – thermoplastics, f – melamine, resistant, g – Bakelite, h – silk, i – cellulose, j – polythene.

One Response to “Synthetic Fibers And Plastics: NCERT Class VIII, Science – Chapter 3”

  1. astha Says:

    What is the difference between synthetic fibers and plastics ?

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