CBSE Class 8 Science Synthetic Fibres and Plastics Important Question and Answers
A.One word Answers
1.Polyester is a long chain polymer of a chemical substance called
Ans.Ester
2.A regenerated synthetic fibre is
Ans.Rayon
3.The first fully synthetic fibre is
Ans.Rayon
4.Name natural polymer
Ans.Cellulose
5.What is the full form of PVC
Ans.Poly vinyl Chloride
6.Acrylic fibres are advantageous over
Ans.Wool
7.Nylon is made from
Ans.Petro chemicals
8.The polymers in which smaller units are linked to each other in straight arrangement are called :-
Ans.Thermoplastics
9.A plastic which can not be softened once moulded into a shape
Ans.Thermosetting plastic
10.The plastic used for making insulation cover of electrical wires
Ans.PVC
11.Rayon clothes are comfortable to wear in
Ans.Summer
12.The first fully synthetic fibre was
Ans.Nylon
13.The non stick coating on pans and other cooking utensils is made from
Ans.Teflon
B.Fill in the blanks
a. ______ fibres are less expensive than natural fi bres.
b. Synthetic fibres are not good absorbers of _____ _ .
c. In______ weather clothes made of synthetic fibre stick to the body.
d. Synthetic fibres catch fire easily so they are _ _____ .
e. Clothes made of synthetic fibres should not be w orn in ______
synthetic, sweat, hot/humid, inflammable, kitch en/laboratory.
2. Fill in the blanks :-
a. ______ burns vigorously and leaves little ash.
b. ______ burns slowly with the smell of burning ha ir.
c. ______ shrinks on burning producing black smoke.
d. ______ burns readily with the smell of burning p aper.
e. ______ shrinks if burnt and forms a black bead a long with sooty flame.
cotton, wool, polyester, rayon, acrylic.
3. Fill in the blanks :-
a. Rayon is prepared from ______ .
b. Polythene is prepared from______ .
c. Nylon is prepared from simple chemicals obtained from ______ .
d. Polyester is made from ______ products.
e. ______ is called a regenerated fibre.
Cellulose, ethylene, coal, petroleum, rayon.
1.Define a thermosetting plastic and give examples.
Ans.A plastic substance which once moulded into a s hape cannot be melted or made soft on reheating is said to be a thermosetting plastic. Hence these plastics cannot be reprocessed and they can maintain their shape and size even at very high temperatures. For example Bakelite and melamine are thermosetting plastics.
2.Why has government banned the use of polythene bags ?
Ans.Polythenes or plastic bags are non biodegradabl e i.e. they cannot be decomposed or recycled by the microorganisms. Besides this an imp roper disposal of polythenes leads to following environmental problems:
i) soil and water pollution.
ii) Blockage and choking of drains and sewer lines .
iii) Death of animals that chew these polythene ba gs along with any food.
3.What are plastics and how are they classified ?
Ans. Plastics are such materials which can be moulde d into a desired form. A variety of day to day usable articles are prepared from plastics s uch as- comb, toothbrush, chair, table, bottle etc. Like synthetic fibres, plastics are also polymers. Platics have been classified into two broad types:
thermoplastic and thermosetting plastics depending upon their ability of getting re processed or not.
4.How did NYLON fabric got this name ?
Ans. Nylon is the first fully synthetic fibre. The n ame nylon was derived from New York (NY) and London (LON) as it was being produced in Ne w York and London at the same time.
5. Why is rayon called a regenerated fibre ?
Ans. We can describe rayon as a regenerated fibre be cause the original raw material used for making rayon is cellulose. The cellulose is bro ken down and then reformed to yield rayon fibers. For this reason rayon is called as a regenerated fibre.
6.Describe the need for making polymers ?
Ans.Properties of polymers make them very useful. S ome of them are:
i) they do not corrode or rust.
ii) they can be produced in various colours.
iii) they can be moulded into different shapes.
iv) they are comparatively cheap or inexpensive.
v) they are quite strong.
7.How are plastics good as well as bad to us ?
Ans.Plastics are good because they are light in wei ght, strong and durable, do not allow heat and electricity to flow through them, non-reac tive and cheaper than metals.
Plastics are bad because they are non biodegradabl e substances i.e. they do not decompose to harmless substances through the action of air, water and microbes over a period of time hence accumulate and cause polluti on.
8. How can we contribute to reduce hazards of plas tics ?
Ans.We must use plastic products to lesser extent, we must try to recycle and atleast reuse the plastic materials, we must use either paper or cloth bags for carrying good instead of using polythene bags, we must create awareness a mong people about excessive use of plastics etc.
9. a) Define polymerisation?
Ans. a)The process which involves combining of a lar ge number of simple molecules chemically so as to form a giant molecule is known as polymerisation.
b) For making synthetic polymers where from we get small molecules?
Ans. b) Small molecules which form long chains of polym ers are obtained from petroleum and natural gas.
8. What are plant and animal fibres ?
Ans.Plant and animal fibres are natural polymers and obtained from plant and animal sources respectively. Cotton and jute are plant fib res while wool and silk are animal fibres.
9.Explain why plastic containers are flavored for sto ring food.
Ans.The main advantage of using plastic for storing foo d are-
a. Plastic has light weight.
b. Good strength.
c. Easy to handle.
10.‘Avoid plastics as far as possible’. Comments on th is advise
Ans. Since, plastics takes several years to decompo se, it is not environment friendly and causes environmental pollution. On combustion, plas tic do not burn completely and produce lots of carbon monoxide gas along with resi dual particles into the atmosphere. These gases cause air pollution and gre en-house effect that may leads to global warming.
11.Explain the difference between thermoplastic and th ermosetting plastics.
A.One word Answers
1.Polyester is a long chain polymer of a chemical substance called
Ans.Ester
2.A regenerated synthetic fibre is
Ans.Rayon
3.The first fully synthetic fibre is
Ans.Rayon
4.Name natural polymer
Ans.Cellulose
5.What is the full form of PVC
Ans.Poly vinyl Chloride
6.Acrylic fibres are advantageous over
Ans.Wool
7.Nylon is made from
Ans.Petro chemicals
8.The polymers in which smaller units are linked to each other in straight arrangement are called :-
Ans.Thermoplastics
9.A plastic which can not be softened once moulded into a shape
Ans.Thermosetting plastic
10.The plastic used for making insulation cover of electrical wires
Ans.PVC
11.Rayon clothes are comfortable to wear in
Ans.Summer
12.The first fully synthetic fibre was
Ans.Nylon
13.The non stick coating on pans and other cooking utensils is made from
Ans.Teflon
B.Fill in the blanks
a. ______ fibres are less expensive than natural fi bres.
b. Synthetic fibres are not good absorbers of _____ _ .
c. In______ weather clothes made of synthetic fibre stick to the body.
d. Synthetic fibres catch fire easily so they are _ _____ .
e. Clothes made of synthetic fibres should not be w orn in ______
synthetic, sweat, hot/humid, inflammable, kitch en/laboratory.
2. Fill in the blanks :-
a. ______ burns vigorously and leaves little ash.
b. ______ burns slowly with the smell of burning ha ir.
c. ______ shrinks on burning producing black smoke.
d. ______ burns readily with the smell of burning p aper.
e. ______ shrinks if burnt and forms a black bead a long with sooty flame.
cotton, wool, polyester, rayon, acrylic.
3. Fill in the blanks :-
a. Rayon is prepared from ______ .
b. Polythene is prepared from______ .
c. Nylon is prepared from simple chemicals obtained from ______ .
d. Polyester is made from ______ products.
e. ______ is called a regenerated fibre.
Cellulose, ethylene, coal, petroleum, rayon.
1.Define a thermosetting plastic and give examples.
Ans.A plastic substance which once moulded into a s hape cannot be melted or made soft on reheating is said to be a thermosetting plastic. Hence these plastics cannot be reprocessed and they can maintain their shape and size even at very high temperatures. For example Bakelite and melamine are thermosetting plastics.
2.Why has government banned the use of polythene bags ?
Ans.Polythenes or plastic bags are non biodegradabl e i.e. they cannot be decomposed or recycled by the microorganisms. Besides this an imp roper disposal of polythenes leads to following environmental problems:
i) soil and water pollution.
ii) Blockage and choking of drains and sewer lines .
iii) Death of animals that chew these polythene ba gs along with any food.
3.What are plastics and how are they classified ?
Ans. Plastics are such materials which can be moulde d into a desired form. A variety of day to day usable articles are prepared from plastics s uch as- comb, toothbrush, chair, table, bottle etc. Like synthetic fibres, plastics are also polymers. Platics have been classified into two broad types:
thermoplastic and thermosetting plastics depending upon their ability of getting re processed or not.
4.How did NYLON fabric got this name ?
Ans. Nylon is the first fully synthetic fibre. The n ame nylon was derived from New York (NY) and London (LON) as it was being produced in Ne w York and London at the same time.
5. Why is rayon called a regenerated fibre ?
Ans. We can describe rayon as a regenerated fibre be cause the original raw material used for making rayon is cellulose. The cellulose is bro ken down and then reformed to yield rayon fibers. For this reason rayon is called as a regenerated fibre.
6.Describe the need for making polymers ?
Ans.Properties of polymers make them very useful. S ome of them are:
i) they do not corrode or rust.
ii) they can be produced in various colours.
iii) they can be moulded into different shapes.
iv) they are comparatively cheap or inexpensive.
v) they are quite strong.
7.How are plastics good as well as bad to us ?
Ans.Plastics are good because they are light in wei ght, strong and durable, do not allow heat and electricity to flow through them, non-reac tive and cheaper than metals.
Plastics are bad because they are non biodegradabl e substances i.e. they do not decompose to harmless substances through the action of air, water and microbes over a period of time hence accumulate and cause polluti on.
8. How can we contribute to reduce hazards of plas tics ?
Ans.We must use plastic products to lesser extent, we must try to recycle and atleast reuse the plastic materials, we must use either paper or cloth bags for carrying good instead of using polythene bags, we must create awareness a mong people about excessive use of plastics etc.
9. a) Define polymerisation?
Ans. a)The process which involves combining of a lar ge number of simple molecules chemically so as to form a giant molecule is known as polymerisation.
b) For making synthetic polymers where from we get small molecules?
Ans. b) Small molecules which form long chains of polym ers are obtained from petroleum and natural gas.
8. What are plant and animal fibres ?
Ans.Plant and animal fibres are natural polymers and obtained from plant and animal sources respectively. Cotton and jute are plant fib res while wool and silk are animal fibres.
9.Explain why plastic containers are flavored for sto ring food.
Ans.The main advantage of using plastic for storing foo d are-
a. Plastic has light weight.
b. Good strength.
c. Easy to handle.
10.‘Avoid plastics as far as possible’. Comments on th is advise
Ans. Since, plastics takes several years to decompo se, it is not environment friendly and causes environmental pollution. On combustion, plas tic do not burn completely and produce lots of carbon monoxide gas along with resi dual particles into the atmosphere. These gases cause air pollution and gre en-house effect that may leads to global warming.
11.Explain the difference between thermoplastic and th ermosetting plastics.
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