DAV Class 8 Science Chapter 13 Question Answer – Synthetic Fibres and Plastics

The DAV Class 8 Science Book Solutions and DAV Class 8 Science Chapter 13 Question Answer – Synthetic Fibres and Plastics are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 13 Question Answer – Synthetic Fibres and Plastics

DAV Class 8 Science Ch 13 Solutions – Synthetic Fibres and Plastics

Something To Know

A. Fill in the bleaks:

Question 1.
________ and ________ are examples of natural fibres.
Answer:
Cotton, silk

Question 2.
The simplest molecule of a polymer is known as a ________ .
Answer:
monomer

Question 3.
Rayon is also known as a ________ fibre.
Answer:
regenerated

Question 4.
Nylon is a ________ fibre.
Answer:
synthetic

Question 5.
________ plastics cannot be remoulded again on heating.
Answer:
Thermosetting

B. State true or false for the following statements:

1. Natural fibres are highly resistant to the effects of chemicals like acids and alkalis.
Answer:
False

2. Synthetic fibres absorb very little water
Answer:
True

3. Thermoplastics can be easily remoulded on heating.
Answer:
True

4. The plastic, used for insulating electrical wires, is teflon.
Answer:
False

5. All types of plastics are biodegradable.
Answer:
False

C. Tick (✓) the correct option:

Question 1.
The correct choice, for the box, in the following sequence is-
thermoplastic: PVC; Thermosetting Plastic : [?]
(a) Nylon
(b) Polystyrene
(c) Bakelite
(d) Polythene
Answer:
(c) Bakelrce

Question 2.
Which of the following is also known as the “wonder polymer’?
(a) Nylon
(b) Polystyrene
(c) Polythene
(d) Acrylic
Answer:
(a) Nylon

Question 3.
A highly durable synthetic fibre used for making parachutes and ropes for rock climbing and fishing nets, is-
(a) Rayon
(b) Nylon
(c) Terylene
(d) PET
Answer:
(b) Nylon

Question 4.
Which of the following is NOT one of the characteristics of synthetic fibres?
(a) Easy to clean and dry quickly.
(b) Long lasting lustre.
(c) Biodegradable.
(d) Do not shrink on washing.
Answer:
(c) Biodegradable.

Question 5.
Melamine is a thermosetting plastic; for it one can say thfat-
(a) It can be easily remoulded on heating.
(b) It cannot resist fire.
(c) It has a cross-linked arrangement of molecules.
(d) Its ‘tolerance’ towards heat is very much lower than those of other plastics.
Answer:
(c) It has a cross-linked arrangement of molecules.

Question 6.
Which of the following is a correct statement about synthetic plastics?
(a) Thermoplastics cannot be deformed easily on heating.
(b) Synthetic plastics are biodegradable.
(c) Synthetic plastics get easily affected by acids and alkalis.
(d) Synthetic plastics have quite high tensile strengths.
Answer:
(d) Synthetic plastics have quite high tensile strengths.

D. Answer the following questions in brief:

Question 1.
Define the term synthetic fibres’.
Answer:
Man-made fibre is called synthetic fibre.

Question 2.
Write two uses of rayon.
Answer:
For making ropes for mountaineering, for making parachute

Question 3.
Name two to three articles that can be made from nylon.
Answer:
Socks, shoes, bags

Question 4.
Why are clothes made from synthetic fibres uncomfortable in summer?
Answer:
Synthetic fibre does not allow air to pass through it. It does not absorb water. A cloth made from synthetic fibre prevents the body heat from escaping the body. Due to this, clothes made from synthetic fibres are uncomfortable in summer.

Question 5.
Give two examples each of the thermoplastics and thermosetting plastics.
Answer:
Thermoplastics: Polythene, PVC
Thermosetting Plastics: Melamine, Bakelite

E. Answer the following questions:

Question 1.
How is a ‘regenerated fibre’ different from a true synthetic fibre? Give one example of each of these two types of fibres.
Answer:
When a fibre is made from processing of natural fibres, it is called regenerated fibres. But a true synthetic fibre is not made from natural fibres. Rayon is a regenerated fibre, while nylon is a true synthetic fibre.

Question 2.
Why do clothes made of nylon last longer?
Answer:
Nylon is highly durable and strong. It does not get affected by acids or alkalis. Due to this, nylon clothes last longer.

Question 3.
Write two points of differences between thermosetting plastics and thermoplastics.
Answer:

Thermosetting plastics	Thermoplastics
Cannot be remoulded by heating.	Can be remoulded by heating.
Has cross-linked arrangement of molecules.	Has linear arrangement of molecules.

Question 4.
State any three advantages of synthetic fibres.
Answer:
Following are the three advantages of synthetic fibres:

• They are durable.
• They are strong.
• They are resistant to action by acids and alkalis.

Question 5.
Give your views on the following: ‘Excessive use of plastics is a threat to environment’.
Answer:
Many types of plastic cannot be recycled. Moreover, plastic is non-biodegradable. So, plastic waste keeps on accumulating in our environment. It turns the soil unfertile. It harms stray animals. It chokes the drains. Due to this, excessive use of plastics is a threat to environment.

Question 6.
Why is Bakelite a good choice for making electrical switches and handles of cooking utensils?
Answer:
Bakelite is resistant to high temperature. It is a bad conductor of heat and electricity. Hence, Bakelite is a good choice for making electrical switches and handles of cooking utensils.

Value Based Question

Ankita is a keen and observant student of Science. She felt concerned when she noticed that the lady, who had joined their household for working in their kitchen, was wearing a nylon saree. She told her mother about the danger of using such a saree in the kitchen. Her mother immediately bought two cotton sarees for that lady and politely advised her to wear them only while working in the kitchen.

Question 1.
State the values displayed by Ankita and her mother.
Answer:
Concern for safety of others and safety at home.

Question 2.
Give reason(s) that make it unsafe to use a nylon saree in the kitchen.
Answer:
Nylon is highly inflammable. It can easily catch fire. Hence, a nylon saree is unsafe in kitchen.

Question 3.
Have a ‘group discussion’ in which different students give their suggestions/ opinions about making the kitchen a ‘safe working place’.
Answer:
Do it yourself.

Something To Do

Question 1.
Take three big plastic containers. In the first, add a few pieces from a polythene bag and fill it with garden soil. In the second, add pieces ot paper and fill it with garden soil. In the third, add vegetable waste from your kitchen and fill it with garden soil. Keep the three containers on the roof and water them for 7-10 days. Check after 10 days and find out which material undergoes decomposition faster. Make a project report on the above activity.
Answer:
Do it yourself.

Question 2.
Visit a few families in your neighbourhood and enquire about the kind of clothes they use, the reason for their choice and advantages of using them. Make a short report on your findings.
Answer:
Do it yourself.

Question 3.
Design posters, with ‘catchy slogans’ and ‘relevant pictures’, to spread awareness about the judicious use of plastics.
Answer:
Do it yourself.

DAV Class 8 Science Chapter 13 Solutions – Synthetic Fibres and Plastics Important Questions and Answers

I. Fill in the blanks:

1. ________ fibres come from either plants or animals.
Answer:
Natural

2. ________ is not a truly synthetic fibre.
Answer:
Rayon

3. ________was the first truly synthetic fibre.
Answer:
Nylon

4. Many monomers are joined to form a ________ .
Answer:
Polymer

5. Thermosetting plastics are ________ monomers.
Answer:
cross-linked

II. Tick (✓) the correct answer:

Question 1.
Which of the following is also known as ‘poor man’s silk’?
(a) Rayon
(b) Acrylic
(c) Nylon
(d) PET
Answer:
(a) Rayon

Question 2.
Which of the following resembles wool?
(a) Rayon
(b) Nylon
(c) Acrylic
(d) Terylene
Answer:
(c) Acrylic

Question 3.
Melamine is used for making which of these?
(a) Toys
(b) Cooker handle
(c) Kitchenware
(d) Insulation for electric wire
Answer:
(c) Kitchenware

Question 4.
Bakelite is used for making which of these?
(a) Toys
(b) Electric switches
(c) Kitchenware
(d) Bottles
Answer:
(b) Electric switches

Question 5.
Which of these is not environment friendly?
(a) Paper bag
(b) Jute bag
(c) Cotton bag
(d) Plastic bag
Answer:
(d) Plastic bag

III. Answer the following questions:

Question 1.
What are monomers?
Answer:
A fibre is composed of simple molecules which are joined to form a long chain. These simple molecules are called monomers.

Question 2.
Why is rayon not considered as truly synthetic fibre?
Answer:
Rayon is made from cellulose which comes from plants. Due to this, rayon is not considered as truly artificial fibre.

Question 3.
What are the various uses of rayon?
Answer:
Uses of Rayon:

• It is mixed with cotton to make bed sheets. It is mixed with wool to make carpets.
• Rayon can be easily dyed in a wide range of colours.
• It is used in making apparels, e.g. dresses, jackets, linings, suits, hats, etc.
• It is used in making many industrial products; iibe surgical products and tyre cords.

Question 4.
What are the various uses of nylon?
Answer:
Uses of Nylon:

• Nylon is highly elastic, tensile and has silk-like appearance. Due to this, it is used in carpets and socks.
• Nylon is used in many military applications; like ropes, parachutes, etc.
• It is highly durable and hence is used in making seat belts, tyre cords, clothes, etc.
• It is used for making many household items; like toothbrushes, combs, hooks, etc.
• It is used for making ropes for rock climbing and fishing nets.

Question 5.
What are the advantages of synthetic fibre?
Answer:
Advantages of Synthetic Fibres:

• They have long-lasting lustre.
• They more durable; compared to natural fibres.
• They are easy to clean and dry very quickly.
• They are wrinkle free and do not need ironing.
• They do not shrink on washing.
• They are less expensive than natural fibres.

Question 6.
What are the disadvantages of synthetic fibre?
Answer:
Disadvantages of Synthetic Fibres:

• They have very low melting point and they burn to form small sticking beads at high temperature. They are a potential fire hazard.
• They don’t absorb sweat and hence it is uncomfortable to wear them; especially in summer and rainy seasons.
  Synthetic fibres are not biodegradable and thus cause lot of pollution.

Question 7.
What are linear and cross-linked arrangements of monomer?
Answer:
There are two types of arrangement of monomers in plastics, i.e. linear arrangement and cross-linked arrangement.
(a) Linear Arrangement: In this arrangement, the monomers are arranged in a straight chain. Plastics formed because of linear arrangement are generally known as thermoplastic.
(b) Cross-linked Arrangement: In this arrangement, the monomers are formed from cross-linked chains of monomers. This type of plastic is generally known as thermosetting plastic.

IV. Projects:

Question 1.
Collect threads of cotton, wool, jute and nylon. Try to break them by your hand.
Find out which of them is having high tensile strength.
Answer:
Do it yourself.

Question 2.
Make a poster on ‘Say No to Plastic Bag’.
Answer:
Do it yourself.