Science Ncert_exemplar 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 Science Ncert_exemplar 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 Science Ncert_exemplar 2019 Solutions. All Science Ncert_exemplar 2019 Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

Page No 13:

Question 1:

Pick the synthetic fibre out of the following?
(a) Cotton 
(b) Nylon
(c) Jute
(d) Wool

Answer:

The synthetic fibre out of the following is nylon as it is made without using any natural raw material.

Hence, the correct answer is option (b).

Page No 13:

Question 2:

Which of the following is a source of rayon?
(a) Wool 
(b) PET
(c) Wood pulp
(d) Silk

Answer:

Rayon is manufactured by the chemical treatment of wood pulp which contains cellulose that occurs naturally.

Hence, the correct answer is option (c).

Page No 13:

Question 3:

Polycot is obtained by mixing
(a) nylon and wool
(b) polyester and wool
 (c) nylon and cotton
(d) polyester and cotton

Answer:

When polyester is mixed with cotton, polycot is obtained.

Hence, the correct answer is option (d).

Page No 13:

Question 4:

Which is a thermosetting plastic?
(a) Melamine 
(b) Polythene
(c) PVC
(d) Nylon

Answer:

The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics. For example: Melamine and bakelite.

​Hence, the correct answer is option (a).

Page No 13:

Question 5:

The material similar to silk in appearance is
(a) Nylon 
(b) Rayon
(c) Polyester
(d) Terylene

Answer:

The material similar to silk in appearance is rayon. Therefore, rayon is also called artificial silk.

Hence, the correct answer is option (b).

Page No 13:

Question 6:

The most suitable material for the preparation of handles of cooking utensils is
(a) Polythene 
(b) PVC
(c) Nylon
(d) Bakelite

Answer:

Bakelite is used for making the handles of various cooking utensils because it is a poor conductor of heat and does not become soft on heating.

​Hence, the correct answer is option (d).

Page No 13:

Question 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

Answer:

Plastics are non-reactive, light in weight, durable and bad conductors of electricity.

Hence, the correct answer is option (d).

Page No 13:

Question 8:

Which of the following represents the correct match for items in Column A with those in Column B
Column A                     Column B
I. Nylon                     (i) Thermoplastic
II. PVC                     (ii) Thermosetting plastic
III. Bakelite              (iii) Fibre
(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)

Answer:

The correct match between column A and column B is given as:
(I)-(iii), (II)-(i), (III)-(ii)

Hence, the correct answer is option (b).



Page No 14:

Question 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

Answer:

PVC, polyethene and bakelite - all are synthetic substances.

Hence, the correct answer is option (c).

Page No 14:

Question 10:

The material which is commonly used for making kitchen containers is
(a) PVC 
(b) Acrylic
(c) Teflon
(d) PET

Answer:

PET i.e., poly-ethyleneterephthalate is used for making kitchen containers as it is very light weight, durable and non reactive.

​Hence, the correct answer is option (d).

Page No 14:

Question 11:

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

Answer:

The chemical name of the natural polymer of cotton is cellulose.

Page No 14:

Question 12:

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

Answer:

The common name of the fibre which is obtained by the chemical treatment of wood pulp is rayon. It is also known as artificial silk.

Page No 14:

Question 13:

Terrycot is made by mixing two types of fibres. Write the names of the fibres. 

Answer:

Terrycot is made by mixing two fibres namely terylene and cotton.

Page No 14:

Question 14:

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

Answer:

Plastic articles are available in all possible shapes and sizes because they can be easily moulded to make a variety of objects.

Page No 14:

Question 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?

Answer:

The disposal of plastic waste is a major problem as plastic is non-biodegradable and takes several years to decompose. Therefore, they cause environmental pollution. Hence, it is advised to avoid the use of plastics as far as possible.

Page No 14:

Question 16:

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

Answer:

It is not advisable to burn plastic and synthetic fibres because on burning they produce a large amount of poisonous gases which can lead to air pollution.

Page No 14:

Question 17:

Select the articles from the following list which are biodegradable.
(a) paper 
(b) woolen clothes
(c) wood 
(d) aluminium can
(e) plastic bag
(f) peels of vegetables

Answer:

Materials which get decomposed through natural processes (such as action of bacteria) are called biodegradable materials. The following articles are biodegradable:
(a) paper
(b) woolen clothes
(c) wood
​(f) peels of vegetables

Page No 14:

Question 18:

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

Answer:

Plastic is non-reactive material. When left exposed to moisture and air, it does not react with air and water. Whereas iron being a reactive metal reacts with moisture and air and leads to the fomation of a reddish brown substance on its surface which is known as rust.



Page No 15:

Question 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?

Answer:

He selected nylon ropes instead of ropes made of cotton or jute because nylon ropes are strong, elastic and lighter in comparison to cotton or jute ropes.
 

Page No 15:

Question 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?

Answer:

She preferred to buy an acrylic blanket because acrylic blankets are cheap, light in weight, more durable and are available in variety of colours and designs. Also, they can be easily washed at home.

Page No 15:

Question 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?

Answer:

The major difference between the two types of plastics is that thermoplastics can be deformed or bent easily on heating. Whereas, thermosetting plastics when moulded once cannot be softened on heating.

Page No 15:

Question 22:

Fill in the blanks.
(i) A polymer is a chain of many small units joined together which are called ______.
(ii) The synthetic fibres are also known as ______ fibres.
(iii) The first fully synthetic fibre was ______.
(iv) A fibre similar to wool is ______.
(v) A plastic used for making crockery is ______.

Answer:

(i) A polymer is a chain of many small units joined together which are called monomers.
(ii) The synthetic fibres are also known as man-made fibres.
(iii) The first fully synthetic fibre was nylon.
(iv) A fibre similar to wool is acrylic.
(v) A plastic used for making crockery is melamine.

Page No 15:

Question 23:

Match items in List A with the items of list B.
List A                                             List B
(a) nylon                               (i) non-stick coating
(b) PET                                (ii) electric switches
(c) rayon                              (iii) parachutes
(d) thermosetting plastics    (iv) polyester
(e) teflon                               (v) artificial silk

Answer:

The correct match between list A and list B is given as:
(a)-(iii), (b)-(iv), (c)-(v), (d)-(ii), (e)-(i)

Page No 15:

Question 24:

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

(a) anory
(b) lopmery
(c) relyteen
(d) laspict
(e) yespolter
(f) felton 

Answer:

(a) Rayon
(b) Polymer
(c) Terylene
(d) Plastic
(e) Polyester
(f) Teflon



Page No 16:

Question 25:

Indicate whether the following statements are True or False. Also write the false statements in their correct form.
(i) The fabric terywool is obtained by mixing terylene and wool.
(ii) Synthetic fibres do not melt on heating.
(iii) It is risky to wear synthetic clothes while working in the kitchen.
(iv) Most of the plastics are biodegradable.

Answer:

(i) True
(ii) False, synthetic fibres melt on heating.
(iii) True
(iv) False, most of the plastics are non biodegradable.

Page No 16:

Question 26:

Write the importance of synthetic polymers in our life.

Answer:

The importance of synthetic polymers in our life is as given below:
1. Nylon: It is used for making ropes for rock climbing, fishing nets, raincoats, parachutes and tyre cords, etc.
2. Acrylic: It is used to make sweaters, blankets, shawls etc.
3. Rayon: It is used to make containers, carpets, car upholstery etc.
4. PET: It is used to make bottles, utensils, films, wires etc.

Page No 16:

Question 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?

Answer:

It is advised to restrict the use of plastic because of the following reasons:

  • The articles mades of plastics are non-biodegradable. They do not decompose (or rot) easily. This causes a great problem in the disposal of plastic wastes.
  • ​The burning of plastic wastes gives out harmful gases which pollute the air. So, it is not advisable to dispose of the used plastic articles by burning.
​Some ways to limit its consumption are:
  • Reducing the use of plastics. Whenever possible use paper bags instead of plastic bags.
  • Reusing it for some other purpose thereby decreasing its consumption.
  • ​Recycling of plastic. It requires the plastic to be collected, sorted, chopped, melted and remoulded.

Page No 16:

Question 28:

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

Answer:

The activity can be performed as follows:

  • Take an iron stand with a clamp and a cotton thread of about 65 cm length.
  • Tie the thread to the clamp so that it hangs freely as shown in figure.
  • At the free end suspend a pan so that weight can be placed in it.
  • Add weight one by one till the thread breaks.
  • Note down the total weight required to break the thread. This weight indicates the strength of the fibre.
  • Repeat the same activity with threads of wool, silk and nylon.


Conclusion: It is observed that the weight required to break the threads of wool, silk and nylon is more than cotton. Therefore, synthetic fibres are stronger than cotton. The increasing order of strength of these threads can be represented as follows:

Cotton < Wool < Silk < Nylon

Page No 16:

Question 29:

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

Across
1. Substance used as synthetic wool (7)
2. A plastic used for making containers and carry bags (9)
3. Substance made up of large number of smaller molecules (7)
4. Another name for this compound is artificial silk (5)
Down
5. A type of fibre obtained naturally from cocoon (4)
6. A synthetic fibre classified as polyester (8)
7. A polymer used for making rope (5)

Answer:


Across
1. Acrylic
2. Polyethene
3. Polymer
4. Rayon

Down
5. Silk
6. Terylene
7. Nylon



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