NCERT Class 8 Science Exemplar Chapter 3 - Synthetic Fibres And Plastics

Chapter 3 - Synthetic Fibres And Plastics

Multiple Choice Questions
Question 1: Pick the synthetic fibre out of the following?
a) Cotton
b) Nylon
c) Jute
d) Wool
Answer:
b) Nylon

Question 2: Which of the following is a source of rayon?
a) Wool
b) PET
c) Wood pulp
d) Silk
Answer:
c) Wood pulp

Question 3: Polycot is obtained by mixing
a) nylon and wool
b) polyester and wool
c) nylon and cotton
d) polyester and cotton
Answer:
d) polyester and cotton

Question 4: Which is a thermosetting plastic?
a) Melamine
b) Polythene
c) PVC
d) Nylon
Answer:
a) Melamine

Question 5: The material similar to silk in appearance is
a) Nylon
b) Rayon
c) Polyester
d) Terylene
Answer:
b) Rayon

Question 6: The most suitable material for the preparation of handles of cooking utensils is
a) Polythene
b) PVC
c) Nylon
d) Bakelite
Answer:
d) Bakelite

Question 7: Which of the following is not a common property of plastics?
a) Non-reactive
b) Light in weight
c) Durable
d) Good conductor of electricity
Answer:
d) Good conductor of electricity

Question 8: Which of the following represents the correct match for items in Column A with those in Column B.
Column A                   Column B
I. Nylon                       (i) Thermoplastic
II. PVC                       (ii) Thermosetting plastic
III. Bakelite                (iii) Fibre
a) I-(ii), II-(iii), III-(i)
b) I-(iii), II-(i), III-(ii)
c) I-(ii), II-(i), III-(iii)
d) I-(iii), II-(ii), III-(i)
Answer:
b) I-(iii), II-(i), III-(ii)

Question 9: Which of the following groups contain all synthetic substances?
a) Nylon, Terylene, Wool
b) Cotton, Polycot, Rayon
c) PVC, Polythene, Bakelite
d) Acrylic, Silk, Wool
Answer:
c) PVC, Polythene, Bakelite

Question 10: The material which is commonly used for making kitchen containers is
a) PVC
b) Acrylic
c) Teflon
d) PET
Answer:
d) PET

Very Short Answer Questions
Question 11: Cotton is a natural polymer. What is its chemical name?
Answer:
Its chemical name is Cellulose.

Question 12: A synthetic fiber which looks like silk is obtained by chemical treatment of wood pulp. It is, therefore, known as artificial silk. What is its common name?
Answer:
The synthetic fiber common name is rayon.

Question 13: Terrycot is made by mixing two types of fibres. Write the names of the fibres.
Answer:
Terrycot is made Terylene and Cotton.

Question 14: Plastic articles are available in all possible shapes and sizes. Can you tell why?
Answer:
Plastic articles are available in all possible shapes and sizes because it can be easily moulded in different shapes.

Question 15: Plastic is used for making a large variety of articles of daily use and these articles are very attractive. But it is advised to avoid the use of plastic as far as possible. Why?
Answer:
Plastic is used for making a large variety of articles of daily use and these articles are very attractive but it is advised to avoid the use of plastic as far as possible as it is non-biodegradable. And hence it causes environmental pollution.

Question 16: Why is it not advisable to burn plastic and synthetic fabrics?
Answer:
It is not advisable to burn plastics and synthetic fabrics because these synthetic fabrics and plastics are made up of chemicals as they contain carbon and hydrogen monomers which can be highly flammable, and once they ignite, they produce flammable gases that can fuel a fire further.

Question 17: Select the articles from the following list which are biodegradable.
a) paper
b) woolen clothes
c) wood
d) aluminium can
e) plastic bag
f) peels of vegetables
Answer:
The items which are biodegradable are
a) paper
b) woolen clothes
c) wood
f) peels of vegetables

Question 18: A bucket made of plastic does not rust like a bucket made of iron. Why?
Answer:
Plastic bucket doesn’t rust like a bucket made of iron because it is a non-reactive material. It does not react with air and water and thus does not rust.

Question 19: Rohit took with him some nylon ropes, when he was going for rock climbing. Can you tell why he selected nylon ropes instead of ropes made of cotton or jute?
Answer:
Rohit selected nylon ropes instead of ropes made of cotton or jute because these nylon ropes are strong, elastic and lighter as compared to cotton and jute ropes.

Question 20: A lady went to the market to buy a blanket. The shopkeeper showed her blankets made of acrylic fibres as well as made of wool. She preferred to buy an acrylic blanket. Can you guess why?
Answer:
The lady preferred to buy an acrylic blanket as acrylic blankets are cheap, light in weight, more durable and are available in variety of colours and designs. They can be easily washed at home.

Question 21: PVC (polyvinyl chloride) is a thermoplastic and is used for making toys, chappals, etc. Bakelite is a thermosetting plastic and is used for making electrical switches, handles of various utensils, etc. Can you write the major difference between these two types of plastics?
Answer:
Thermoplastics get deformed easily on heating and can be bent easily on heating. On the other hand thermosetting plastics when molded once cannot be softened on heating.

Question 22: Fill in the blanks.
i) A polymer is a chain of many small units joined together which are called ______.
ii) The synthetic fibres are also known as ______ fibres.
iii) The first fully synthetic fibre was ______.
iv) A fibre similar to wool is ______.
v) A plastic used for making crockery is ______.
Answer:

i) A polymer is a chain of many small units joined together which are called monomer.
ii) The synthetic fibres are also known as man-made fibres.
iii) The first fully synthetic fibre was nylon.
iv) A fibre similar to wool is acrylic.
v) A plastic used for making crockery is melamine.

Question 23: Match items in List A with the items of list B.
List A List B
List A                                                              List B
(a) nylon                                                         (i) non-stick coating
(b) PET                                                           (ii) electric switches
(c) rayon                                                         (iii) parachutes
(d) thermosetting plastics                             (iv) polyester
(e) teflon                                                         (v) artificial silk
Answer:

(a) nylon - parachutes
(b) PET - polyester
(c) rayon - artificial silk
(d) thermosetting plastics - electric switches
(e) teflon - non-sticking coating

Question 24: Unscramble the jumbled words given below, related to synthetic materials.
a) anory
b) lopmery
c) relyteen
d) laspict
e) yespolter
f) felton
Answer:

a) Rayon
b) Polymer
c) Terylene
d) Plastic
e) Polyester
f) Teflon

Long Answer Questions
Question 25: Indicate whether the following statements are True or False. Also write the false statements in their correct form.
i) The fabric terywool is obtained by mixing terylene and wool.
ii) Synthetic fibres do not melt on heating.
iii) It is risky to wear synthetic clothes while working in the kitchen.
iv) Most of the plastics are biodegradable.
Answer:

i) True
ii) False; Synthetic fibres melt on heating
iii) True
iv) False; Most of the plastics are non-biodegradable.

Question 26: Write the importance of synthetic polymers in our life.
Answer:

→ Rayon - Rayon is mixed with fibre glass for making helmets. It is used to make jackets and tracksuits. It is also used to make curtains because it drapes well.
→ Nylon - It is used for making ropes because it is very strong. It is also used to make ropes, raincoats, fishing nets etc.
→ Polyester - Polyester is used for making magnetic audio and video cassettes and floppy disks. It is also highly suitable for shirting, suiting, sarees and draperies mixed with fibre glass for moulding it into helmets, protective sheets and hulls in boats

Question 27: Despite being very useful it is advised to restrict the use of plastic. Why is it so? Can you suggest some methods to limit its consumption?
Answer:
Plastic is a non-biodegradable material and hence it causes pollution. At the same time burning such materials in the form of garbage causes serious air pollution. Some ways to limit its consumption are: Reducing the use of plastics. Whenever possible use paper bags instead of plastic bags, reusing it for some other purpose thereby decreasing its consumption, recycling of plastic. It requires the plastic to be collected, sorted, chopped, melted and remoulded.

Question 28: Write an activity to show that synthetic fibres are stronger than the cotton fibres.
Answer:
Take an iron stand with a clamp. Take a cotton thread of about 60 cm length. Tie it to the clamp so that it hangs freely from it. At the free end suspend a pan so that weight can be placed in it. Add weight one by one till the thread breaks. Note down the total weight required to break the thread. This weight indicates the strength of the fibre. Repeat the same activity with threads of wool, polyester, silk and nylon.

Question 29: Complete the crossword given below with the help of clues.

Answer:


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