Chapter 3, Class 8 NCERT Science -
Synthetic Fibers and Plastics
CBSE Sample Questions Answers
Key Terms
Synthetic Fiber Synthetic fibers are made of very large units called
‘polymer’. The synthetic fibers are obtained by chemical processing of petrochemicals.
Different types of synthetic fibers are like - rayon, nylon, polyester etc.
Polymer The word ‘Polymer’ comes from two Greek words:
‘poly’ means many and ‘mer’ means part or unit. When smaller units of as
chemical substance are combined to form a large single unit then it is called
polymer. Example - cellulose, polythene etc.
Biodegradable Materials A material which gets decomposed through
natural processes such as, action by bacteria are called ‘biodegradable’
materials. Examples - paper, wood, vegetables etc.
Short answer type CBSE sample questions answers
Question.1: Why rayon is
completely synthetic fiber?
Answer: Rayon is not completely synthetic
fiber because it is not completely made of synthetic materials. It uses tree
pulp as the raw material.
Question.2: What is PET?
Answer: PET is a form of polyester. It
is synthetic material. It is mainly used to make bottles, utensils, films,
wires and many other useful products. The most common and visible usage being
PET jars in our kitchens.
Long answer type CBSE sample questions answers
Question.1: Name different artificial fibers and write their
uses.
Answer: Following are the main synthetic
fibers:
- Rayon - It’s also called the artificial silk as it has great luster and is light in weight. It is obtained by chemical treatment of wood pulp. It can be woven like silk and dyed in different colours. It’s used as dress material. Mixed with cotton, it is used to make curtains, bed-sheets etc. It’s used with wool to make beautiful carpets.
- Nylon - It’s the strongest, 100% manmade fiber. It’s made by coal, water and air. It’s elastic in nature and light in weight. It is lustrous and thus ideal for making dresses. Nylon is also used to make stockings, seat-belts, ropes, tents, toothbrushes, sleeping bags, curtains, parachutes etc.
- Polyester - It is made up of multiple units of ‘esters’. The clothing made of this fiber does not get wrinkled easily. It’s always crisp and easily washable. PET is also derived from polyester which in turn is used to make containers, utensils, films, wires etc.
- Acrylic - Acrylic is like wool and is used to make sweaters and suit lengths.
Question.2: Explain uses
of Melamine and Bakelite.
Answer:
Uses of Melamine - Melamine is a kind of thermosetting plastic
which has great capacity to tolerate heat. It does not allow the heat to pass
through easily. Melamine being a fire-resistant material has many other uses
like in making kitchenware and handles of the cooking ware so that they do not
heat up and remain easy to handle while cooking. It is also used in preparing
fire resistant fabrics.
Uses of Bakelite - Bakelite is a poor conductor of electricity and
does not allow the electric current to pass through it. Therefore, it’s used to
make electric plugs and switches. Because of its heat resistant character it is
used to make handles of utensils.
Question.3:
Write advantages of disadvantages of synthetic fibers.
Answer:
Advantages of synthetic fibers:
1)
Synthetic fibers are generally
wrinkle resistant. So it is convenient to wash and wear.
2)
Synthetic fibers are
strong so they can take up heavy loads easily. They have got high tensile
strength, which enables them to carry weights.
3)
They have great
elasticity and so can be easily stretched.
4)
Synthetic fibers are
generally soft, because of which they used to make variety of clothes and
clothing materials.
Disadvantages of synthetic fibers:
1)
Synthetic fibers
can’t absorb moisture. This makes them unsuitable during summer. When our body
sweats this make body sticky and skin irritating.
2)
They are dangerous to
be worn near fire or heat, as they can easily catch fire.
3)
They are difficult to
iron (press) as they melt very easily.
Question.4: How disposal of plastic is a problem? Explain. or
Why the wastage of plastics is considered against eco-friendly?
Answer: There are several reasons for which the wastage
of plastics is considered not eco-friendly (environment friendly). First of
all, the plastics are non-biodegradable in nature and take several years to
degenerate. Some plastics which cannot be recycled are a great problem to
finally dispose them off. The burning of plastics is also a very slow process
during which they release a lot of poisonous gases to the environment causing
air-pollution. Such plastic items thrown carelessly in an eating garbage they
may cause death for some animals like - cows, dogs etc. The poly-bags, plastic
wrappers etc carelessly thrown here and there are responsible for clogging of
drains. Being non-degradable, such disposed plastic wastes get buried into the
soil resulting soil pollution and decreasing soil fertility. Because of all
these reasons the disposal of plastic remains a genuine problem and wastage of
plastics is also considered as against environment friendly.
Objective type CBSE Questions with their Answers
Question.1: Fill in the
blanks:
a. The fiber we get from plants and animals `is called _______.
b. The fiber we obtain from chemicals is called _______.
c. The chemicals of petroleum origin used to form synthetic
fiber are called _______.
d. Synthetic substances apart from fibers are _______.
e. Plastics which can be bent and moulded are called _______.
f. ______ is used to make the handles of cookware because it is
_______ to heat.
g. Switch board and electric plugs are made of _______.
h. ______ is the most expensive natural fiber.
i. Cotton is the polymer of _____.
j. We should avoid using ________ carry bags.
Answer: a - natural fiber, b - artificial / synthetic
fiber, c - petrochemicals, d - plastics, e - thermoplastics, f - melamine,
resistant, g - Bakelite, h - silk, i - cellulose, j - polythene.
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