Class- 8 Chapter 13 Synthetic Fibres and Plastics | Class- 8 DAV Science Solutions

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DAV Class- 8 Synthetic Fibres and Plastics Question and Answer

Something To Know

A. Fill in the blanks.

1. _______ and _______ are examples of natural fibres.

2. The simplest molecule of a polymer is known as a _______.

3. Rayon is also known as a _______ fibre.

4. Nylon is a _______ fibre.

5. _______ plastics cannot be remoulded again on heating.

Ans. 1. Cotton, silk 2. monomer 3. regenerated 4. synthetic 5. Thermosetting : 1.


B. State true or false for the following statements:

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

2. Synthetic fibres absorb very little water.

3. Thermoplastics can be easily remoulded on heating.

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

5. All types of plastics are biodegradable.

Ans. 1. False 2. True 3. True 4. False 5. False


C. Tick the correct Option:

1.The correct choice, for the box, in the following sequence is—

Ans. Bakelite

2. Which of the following is also known as the ‘wonder polymer’?

Ans. Nylon

3. A highly durable synthetic fibre used for making parachutes and ropes for rock climbing and fishing nets, is—

Ans. Nylon

4. Which of the following is NOT one of the characteristics of synthetic fibres?

Ans. Biodegradable.

5. Melamine is a thermosetting plastic; for it one can say that—

Ans. It has a cross-linked arrangement of molecules.

6. Which of the following is a correct statement about synthetic plastics?

Ans. Synthetic plastics have quite high tensile strengths.


D. Answer the following questions in brief.

1.Define the term ‘Synthetic Fibres’

Ans. Man-Made fibre is called synthetic fibre.

2.Write two uses of Rayon

Ans. Rayon is used in textile industry for making clothing like sarees, blouses, dresses, socks. Rayon is also used in making ropes for mountaineering.

3.Name two to three articles that can be made from nylon.

Ans. Shoes,Socks and Bags

4.Why are clothes made from synthetic fibres uncomfortable in summer?

Ans. The clothes made up of synthetic fibres are not suitable for wearing during hot summer weather as these clothes are extremely fine and do not have sufficient pores for the sweat to come out, evaporate and cool our body. Due to this, clothes made up of synthetic fibres make us feel hot and uncomfortable during summer.

5.Give two examples each of the thermoplastics and thermosetting plastics?

Ans.

Thermosetting PlasticsMelamine, Bakelite
ThermoplasticsPolythene ,PVC


E. Answer the following questions.

1. How is a ‘regenerated fibre’ different from a true synthetic fibre? Give one example of each of these two types of fibres.

Ans. 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.

2. Why do clothes made of nylon last longer?

Ans. Nylon is highly durable and strong. It does not get affected by acids or alkalis. Due to this, nylon clothes last longer.

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

Ans.

Thermoplastics Thermosetting
Thermoplastics have linear arrangement of molecules.Thermosetting plastics have cross-linked arrangement of molecules.
Thermoplastic can be deformed easily on heating and can be remoulded into new shape.Thermosetting plastics cannot be deformed on heating.

4. State any three advantages of synthetic fibres.

Ans. Following are the three advantages of synthetic fibres:

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

5. Give your views on the following: ‘Excessive use of plastics is a threat to environment’.

Ans. The majority of plastics are not recyclable. Plastic is also non-biodegradable. As a result, plastic garbage continues to accumulate in our environment. It depletes the soil’s fertility. It causes harm to stray animals. As a consequence, over usage of plastics poses a risk to the environment.

6. Why is Bakelite a good choice for making electrical switches and handles of cooking utensils?

Ans. Bakelite is a heat-resistant material. It is a poor heat and electrical conductor. Bakelite is thus an excellent material for electrical switches and cooking utensil handles.

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