Synthetic Fibers and Plastics
CBSE Class 8 Science, NCERT Solutions
NCERT Answers – Cbse Ncert Solutions of Chapter Exercise Questions
Question.1: Explain why some fibers are called synthetic?
Solution: Some fibers are called synthetic fibers because they are man-made. These fibers made by the combination of different types of chemicals in industries and their nature are also different in respect of natural fiber.
Question.3: Fill in the blank with appropriate words:
a) Synthetic fibers are also called ____ or ____ fibers.
b) Synthetic fibers are synthesized from raw material called ____.
c) Like synthetic fibers, plastic is also a ____.
Solution: a. man-made or natural fibers, b. petrochemicals c. polymer.
Question.4: Give examples which indicate that nylon fibers are very strong.
Solution: Nylon fibers are very strong, thus they are used to prepare ropes for mountaineering. They are also used to prepare parachutes.
Question.5: Explain why plastic containers are favored for storing food.
Solution: Advantages of storing foods in plastic containers are:
1) The plastics do not react with the food stored in them.
2) The plastics are light weight and are strong.
3) They are easy to handle and safe.
4) They are cheap (affordable) and ductile.
Question.6: Explain the difference between the thermoplastic and thermosetting plastics.
Solution: Difference between thermoplastic and thermosetting plastics is as follows:
1. Thermoplastic is a soft material
2. It can be bent easily
3. It can be melted on heating
4. It can be re-shaped
5. These are good conductors of heat
6. Examples: Polythene, PVC
1. Thermosetting plastic is a hard material
2. It can’t be bent
3. It can’t be melted on heating
4. It can’t be re-shaped
5. These are bad conductors of heat
6. Examples: Bakelite, Melamine
Question.7: Explain why the following are made of thermosetting plastics:
a. Saucepan handles
b. Electric plugs / switches / plug boards.
Answer: a. Saucepan handles are made of thermosetting plastics because it is a bad conductor of heat and so, do not get heated up while cooking. So it is easier to handle the utensil while cooking. Moreover it does not get softened due to heat.
b. Electrical plugs, switches and plug-boards are made up of thermosetting plastics because it is a bad conductor of electricity. It does not allow the electric current to pass through it, thus safe in using in electric appliances.
Question.8: Categorize the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’:
Telephone Instruments, Toys, Cooker handles, Carry bags, Ball point pens, Plastic bowls, Electric wire covering, Plastic chairs, Electrical switches.
Can be recycled: Toys, carry bags, plastic bowls, ball point pen, plastic chair, electric wire covering.
Can’t be recycled: Cooker handles, electrical switches, telephone instruments.
Question.9: Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made of synthetic material? Advise Rana giving your reasons.
Answer: Cotton clothes are preferred to synthetic clothes in summer because cotton is a bad conductor of heat. It does not allow the outer heat to enter in our body, thus protects our body from heat. Also it has more capacity to hold moisture than the synthetic clothes. So, it retains the sweat of the body and keeps it cool.
So Rana should buy shirts made up of cotton.
Question.10: Give examples to show that plastics are noncorrosive in nature.
Answer: Plastics are noncorrosive in nature because it is a nonreactive substance. It does not react with air, water, minerals and other chemicals. So in present days most of the containers, utensils and laboratory equipments are made with plastics to store food, chemicals etc.
Question.11: Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Answer: For the handles and bristles of toothbrush we can not choose same type of plastics because bristles are used to clean our teeth and gum. So it must be a type of thermoplastic that is nylon but handles of toothbrush must be strong and tough so that it can give some grip and resist our efforts on it. So it should a type of thermosetting plastic.
Question.12: ‘Avoid plastics as far as possible’. Comment on this advice.
Answer: We should avoid using plastics as far as possible. The reasons being as below –
- Plastics are non-biodegradable materials. They take several years to decompose.
- Not being eco-friendly, plastics cause environment pollution.
- Burning process of plastics is extremely slow. In the process of burning it releases lots of poisonous gas into the atmosphere causing air pollution.
- Some plastics can’t be recycled even and so, it is very difficult to finally dispose such materials.
- Polythene bags, carelessly thrown in an eating garbage can cause death for the animals like - cows, dogs etc or sometimes even become a cause for clogging of the drains.
The only solution to get rid of these problems is to avoid plastics or use it very judiciously. Hence, there is a logic and justification behind the advice that ‘Avoid plastics as far as possible’.
Question.13: Match the terms of column I correctly with the phrases given in column II:
a. Prepared by using wood pulp
b. Used for making parachutes and stockings
c. Used to make non-stick cook wares
d. Fabrics do not wrinkle easily
Answer: (i) - d (ii) - c (iii) - a (iv) - b
Question.14: ‘Manufacturing synthetic fibers is actually helping conservation of forests’. Comment.
Solution: The natural fibers are obtained from plants and animals, whereas the synthetic fibers are obtained by chemical processing of petrochemicals. Unlike natural fibers, manufacturing of synthetic fibers do not require to cut trees or hunting of any animal. In this way manufacturing synthetic fibers is actually helping conservation forests.
Synthetic Fibers and Plastics | Chapter 3, Class 8 NCERT Science - CBSE Sample Questions with their Answers