NCERT Class 8 Science Chapter 3 - Synthetic Fibres and Plastics

Chapter 3 - Synthetic Fibres and Plastics

Question and Answers
Question 1: Explain why some fibres are called synthetic.
Answer: Some fibres are called as synthetic fibres as these are manmade fibres made by using chemicals. These are made of small units that join together to form long chains. Example: nylon, rayon, acrylic, polyester etc.

Question 2: Give examples which indicate that nylon fibres are very strong.
Answer:
• Parachutes and ropes are made of nylon.
• Nylon is used in making seat belts, fishing nets.

Question 3: Explain why plastic containers are favoured for storing food.
Answer: Plastic containers are favoured for storing food as
• It is non-reactive.
• It is lightweight and strong.
• It is easy to handle and safe.

Question 4: Define
a) Biodegradable: Materials which get decomposed through natural processes are called biodegradable.

b) Non-biodegradable: Those materials which are not easily decomposed by natural processes are called non-biodegradable.

Question 5: Explain the difference between thermoplastic and thermosetting plastics.
Answer:
Thermosetting plastics
• Thermoset plastics are hard and rigid.
• Thermoset can be moulded to set it in any shape but it cannot be remoulded.
• It is dark in color, hard and resistant to heat and electricity.

Thermoplastics
• Thermoplastics are soft and flexible. They are not elastic like rubber and steel springs.
• They melt on warming and regain their shape on cooling.
• Thermoplastics can be drawn into fine fibres, moulded to any desired shape or stretched or spread.

Question 6: Define
a) Rayon: Rayon is also known as artificial silk. It is a man-made fibre made from wood pulp.

b) Polymer: The word “Polymer” comes from two Greek words, poly meaning many and mer meaning part/unit. So polymer is made of many repeating units.

Question 7: Explain why the following are made of thermosetting plastics.
a) Saucepan handles
b) Electric plugs/switches/plug boards
Answer:
a) Thermosetting plastics are used to make saucepan handles because they are insulators of heat and also on heating, they do not get softened.

b) Bakelite is a kind of thermosetting plastic which is insulator of heat and electricity. Due to this it is used for making electric plugs, switches, plug boards, etc.

Question 8: 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 a cotton shirt for the summer and not a synthetic shirt. Cotton is a good absorber of water. So it can soak the sweat coming out of the body and expose it to the environment. Thus, it helps in evaporating the sweat and helps in cooling our body.

Question 9: Give examples to show that plastics are noncorrosive in nature.
Answer: Plastics are non-corrosive in nature, they do not react even if they come in contact with strong chemicals. Example: The cleaning chemicals are stored in plastic bottles, instead of metal containers.

Question 10: ‘Avoid plastics as far as possible’. Comment on this advice.
Answer: We should avoid plastics as far as possible because plastics are non-biodegradable in nature. Once introduced into the environment they cause pollution. If burnt they release poisonous gases and the plastic bags thrown in the garbage dumb are swallowed by animals choke their respiratory system and causes fatalities in animals.

Question 11: Define:
a) Petrochemicals: All the synthetic fibres are prepared by a number of processes using raw materials of petroleum origin, called petrochemicals.