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:
Thermoplastic
|
Thermosetting
Plastics
|
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.
Answer:
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:
Column I
|
Column II
|
(i)
Polyester
(ii)
Teflon
(iii)
Rayon
(iv)
Nylon
|
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
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