Class 8 - Chemistry - Synthetic Fibers and Plastics

Question 1:

Explain why some fibres are called synthetic.

Answer:

The fibres which are not obtained naturally they are prepared artificially by using chemicals. These fibres are known as synthetic fibres.

All the synthetic fibres are prepared by a number of processes using raw materials of petroleum origin, called petrochemicals.

The synthetic fibres are made up of very large units called polymers. Some of the synthetic fibres are rayon, nylon and acryl on.

  • Beads and
  • Paper clips joined to form long chains.

 Class_8_Chemistry_Synthethic_Fibres_SyntheticFibres

 

Question 2:

Mark ( ) the correct answer:

Rayon is different from synthetic fibres because

(a) it has a silk like appearance

(b) it is obtained from wood pulp

(c) its fibres can also be woven like those of natural fibres

Answer:

Correct Option: - it is obtained from wood pulp.

 

 

Question 3:

Fill in the blanks with appropriate words:

(a) Synthetic fibres are also called ______ or _______ fibres.

(b) Synthetic fibres are synthesised from raw material called ________.

(c) Like synthetic fibres, plastic is also a __________.

Answer:

(a) Synthetic fibres are also called man-made or artificial fibres.

(b) Synthetic fibres are synthesised from raw material called petrochemicals.

(c) Like synthetic fibres, plastic is also a polymer.

 

 

Question 4:

Give examples which indicate that nylon fibres are very strong.

Answer:

A nylon thread is elastic and light but actually stronger than a steel wire.

Nylon is a very strong fibre that is why nylon is used for making parachutes, rock climbing ropes, fishing nets seat belts etc.

 Class_8_Chemistry_Synthethic_Fibres_Nylon

 

Question 5:

Explain why plastic containers are favoured for storing food.

Answer:

Plastic containers are favoured for storing food for the following reasons:

  1. Plastic containers are light weight so they are easy to handle.
  2. Their price is very less as compared to other containers.
  3. Good Strength.
  4. They don’t corrode.

 

 

Question 6:

Explain the difference between the thermoplastic and thermosetting plastics.

Answer:

Thermosetting

Thermoplastics

1.     Thermosetting plastic cannot be easily bent but if we force to bend, it will break.

1.     We can bend thermoplastics easily.

2.     On heating thermosetting plastics, it cannot be softened. This is the reason it cannot be reshaped once it is moulded.

2. On heating the thermoplastics, it becomes softened and can be moulded and reshaped easily.

3.     For example: - Bakelite and Melamine.

3. Polythene and PVC are some of the examples of thermoplastics.

 

 

 

Question 7:

Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

(b) Electric plugs/switches/plug boards

Answer:

  1. Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics.
  2. It is used for making saucepan handles.
  3. Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, electric plugs and plug boards, etc.

Question 8:

Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’:

Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, and plastic covering on electrical wires, plastic chairs, and electrical switches.

Answer:

 “Can be recycled”

“ Cannot be recycled”

1.     Plastic toys

1.Telephone instruments

2.     Carry bags

2.Cooker handles

3.     Ball point pens

3.Electrical switches

4.     Plastic bowls

 

5.     Plastic covering on electrical wires

 

6.     Plastic chairs

 

 

 

Question 9:

Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material?

Advise Rana, giving your reason.

Answer:

Rana should buy shirts made of cotton as cotton absorbs sweat and the pores in cotton allows easy evaporation and keeps our body cool.

But synthetic shirts don’t absorb sweat so; they are very uncomfortable to wear in summers.

 

 

Question 10:

Give examples to show that plastics are noncorrosive in nature.

Answer:

Plastics do not react with water and air and also don’t corrode easily.

Therefore plastic like Teflon is used as a coating in all non-stick cookware.

Bakelite is poor conductor of heat and electricity so used in making electric switches and handles of utensils. Also melamine is used is making floor tiles and kitchenware.

Plastic Plates & Electric Switches

 Class_8_Chemistry_Synthethic_Fibres_Plastics

 

Question 11:

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

Answer:

The bristles of a tooth brush should be made of soft material so that it does not harm the gums and the handle

should be made of hard material so that it can give a firm grip.

Therefore, the bristles are made up of nylon fibres which are strong, elastic, lustrous,

light weight and easy to handle and the handle is made of hard plastic as it is strong, durable, poor conductor of heat and electricity.

 Class_8_Chemistry_Synthethic_Fibres_ToothBrush

 

 

Question 12:

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

Answer:

Plastics should not be used for the following reasons:-

  1. They are bio-degradable and take several years to decompose.
  2. They are not environment friendly.
  3. By burning plastics, poisonous fumes are released that cause air pollution.
  4. Besides, the burning process in the synthetic material is quite slow and it does not get completely burnt easily.
  5. Cows and other animals may eat plastics present in the garbage which may choke their respiratory system and even cause death.
  6. Plastic bags drained into the water bodies cause threat to the aquatic life also.

 Class_8_Chemistry_Synthethic_Fibres_PlasticPollution

 

 

Question 13:

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

Column I                               Column II

(i) Polyester                      (a) Prepared by using wood pulp

(ii) Teflon                          (b) Used for making parachutes and stockings

(iii) Rayon                         (c) Used to make non-stick cookware

(iv) Nylon                          (d) Fabrics do not wrinkle easily

Answer:

Column I                              Column II

(i) Polyester                    (d) Fabrics do not wrinkle easily

(ii) Teflon                        (c) Used to make non-stick cookware

(iii) Rayon                       (a) Prepared by using wood pulp

(iv) Nylon                       (b) Used for making parachutes and stockings

 

 

Question 14:

‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment

Answer:

The manufacturing of synthetic fibres is helpful in the conservation of forests because if we use natural fibres,

the raw materials for them have to be derived from the plants, which means cutting off lots of trees.

This leads to deforestation. But raw materials of synthetic fibres are mainly petrochemicals. Hence this proves to be helpful in the conservation of forests.

 

 

 

Question 15:

Describe an activity to show that thermoplastic is a poor conductor of electricity.

Answer:

With the help of an activity it can be shown that a thermoplastic is a poor conductor of electricity.

Things needed are: - A bulb, wires, a battery, a piece of metal and a plastic pipe.

When the current is switched on we will see that the bulb glows in the Figure (1).Whereas in the Figure (2) the bulb does not glow.

This proves that the plastic pipe (thermoplastic) is a poor conductor of electricity.

Figure (1)                                    Figure(2)

 

 Class_8_Chemistry_Synthethic_Fibres_Conductor_&_PlasticPipe

 

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