Std 8 Chem Ch-1 Polymers : Synthetic Fibres and Plastics

Polymers : Synthetic Fibres and Plastics

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1. Fill in the blanks.

  1. The small repeating units in a polymer are called manomile
  2. Royan is also known as artifficial silk.
  3. lalyesta isused for making sails for sailboats.
  4. Bakelite is used for making the handles of cookingutensils.
  5. Plastics derived from natural sources are called bisdgpnhable

2. Mark ‘true’ or ‘false’ against the following statements.

  1. Synthetic fibres cause skin irritations on prolonged contact with human body. True
  2. PVC is a thermosetting plastic. False
  3. Plastics also get corroded like metals, e.g. iron. False
  4. Plastics are used for packaging of tablets. True
  5. Plastics are responsible to some extent for food poisoning. True
3. Match the following terms.
Column I Column II
1) Polyester a) Prepared from wood pulp
2) Melamine b) Used for making parachutes and stockings
3) Rayon c) Used for making kitchenware
4) Nylon d) Fabrics do not wrinkle easily

Ans. –  1) – d) , 2) – c) , 3) – a), 4) – b)

4. What is polymerisation?
Ans. – Polymers are large molecules formed by the combination of a large number of small repeating units. The small repeating units which combine to form a polymer are called monomers.The overall process leading to the formation of polymers from monomers is known as polymerisation.

5. Give a brief account of environmental pollution caused by plastics.
Ans.

Causes :

  • Being non-biodegradable, plastics cannot be decomposed easily and, thus, are retained in the environment.
  • Plastics find their way from land to waterbodies. Thus pollute water also.
  • Burning of plastics releases poisonous fumes into the atmosphere.

Event :

  • Deterioration of environmental conditions in numerous ways due to contamination of air, water and soil by discarded plastics.

Effects :

  • Plastics have an adverse effect on all life forms. They pose a threat to all forms of aquatic life and are very fatal for animals as they die due to choking.
  • In humans,plastics are reported to cause certain reproductive problems and even cancer in some cases.

6. List the practices that should be followed to reduce the environmental pollution caused by plastics.
Ans.

  • The use of plastic bags should be reduced and other alternatives,e.g. jute or hemp bags should be given preference.Bioplastics should be used to a larger extent.
  • Use water bottles,lunch box made from steels instead of plastics.
  • Cover the book with paper instead of plastic cover.
  • The same plastic articles,e.g. plastic bags and plastic bottles should be used repeatedly as much as possible. If such plastic articles become unfit for their usual purposes, some other ways to utilise them should be thought about.
  • Use wooden toothbrush,comb etc.
  • Wherever possible,plastics used and thrown away by consumers and manufacturers should be collected and separated.
  • Discarded plastics should be reprocessed to obtain some other valuable products. This will help reduce the use of fresh plastics,which in turn will bring the extent of environmental pollution down.
7. Discuss the commercial importance of plastics.
Ans.
  • Plastics are strong and light in weight so used in packaging of goods as it reduces weight in transportation
  • In wrappers of food items as they are water resistant,light weight.
  • In construction of building like pipes for water and electric wires,taps,furniture etc as they are poor conductor of heat and electricity.
  • In making of bottles of water,cold drink,shampoo etc as they are strong,durable and cheap.
  • In making of food container and toys as they are lightweight and water resistant.
  • They are poor conductor of electricity so used in parts of car,TV,computers etc.

8. Make a flow chart to show the manufacturing process of synthetic fibers.
Ans. – Synthetic fibre – forming substance → melted → dissolved in suitable solvent → turned into fluid state → pass through holes of spinneret → fibres (write these steps into flow chart form)

9. Explain why synthetic fibres are considered superior to their natural analogues.
Ans. – Because of the following properties of synthetic fibres,they are considered superior to their natural analogues.

  • They are stronger,more elastic,tougher and more durable.
  • They are clour-fast and do not bleed colour when washed.
  • They are easy to wash and easy to dry.
  • They retain creases longer and do not wrinkle.
  • They do not shrink when washed.
  • They are resistant to attacks by insects.
10. Distinguish between thermoplastics and thermosetting plastics.
Ans.
Thermoplastics Thermosetting Plastics
Definition Plastics which melt on heating and can be remoulded easily. When cooled they freeze to a glassy,brittle state and break if forcefully bent. Plastics which cannot be deformed on heating once they have been moulded to a definite shape,i.e. they are not remouldable.
Structure Combining units are linked to one another in a linear manner. Combining units are cross-linked.
Examples Polythene and PVC Melamine and bakelite
Uses Polythene and PVC are used to make toys,combs,pipes and containers. Melamine is used for making fire-resistant plastics, kitchenware and floor tiles as it resists fire.Bakelite is used for making electric switches and handles of utensils as it does not conduct heat and electricity.
11. Compare and contrast the physical properties of plastics with those of synthetic fibres.
Ans.
Plastics Synthetic Fibres
Plastics are heat-resistant. e.g. melamine They are not heat-resistant.
Plastics are non-reactive,that is, they are not attacked by chemicals. They are reactive with chemicals like
They are non-biodegradable. They are also non-biodegradable.
They are waterproof. They are not waterproof.
They can be moulded easily. They can’t be remoulded.
They are strong, lightweight and durable. They are also strong,lightweight and durable.
They are resistant to attacks by insects. They are also resistant to attacks by insects.

12. Which properties of plastics enable them to be moulded in all possible shapes and sizes?
Ans. – because plastics melt easily on heating and can be easily moulded by cooling in all possible shape and size.

13. Illustrate the three different modes of arrangement of linking units in polymers.
Ans.
  1.  linear arrangement of monomers : Monomeric units join together to form long chains. (draw figure from textbook)
  2. Branched-chain arrangement of monomers : Monomeric units form long chains with some branches along the main chain. (draw figure from textbook)
  3. Cross-linked arrangement of monomers : Monomeric units form rigid three dimensional network-like structure. (draw figure from textbook)
14. How can you implement the 4-R principle in your daily lives?
Ans.
  1. Reduce : The use of plastic bags should be reduced and other alternatives, e.g. jute or hemp bags.
  2. Reuse : The same plastic articles e.g. plastic bags and plastic bottles should be used repeatedly as much as possible.
  3. Recover : Whenever possible,plastics used and thrown away by consumers and manufacturers should be collected and seperated.
  4. Recycle : Discarded plastic should be re-processed to obtain some other valuable products. This will help reduce the use of fresh plastics, which in turn will bring the extent of environmental pollution down.

15. Why are electrical wires provided with plastic coverings?
Ans. –  Plastics are non-reactive and poor conductors of electricity. They do not allow the electric current to pass through them easily. so, covering electrical wiring using plastic ensures that the current doesn’t flow outside the wires and protect us from getting shocks.

16. Explain why plastic containers are favoured over other materials for storing food.
Ans. – Plastics are non-reactive,that is, they are not attacked by chemicals. Therefore,they are used to make containers for storing food.

17. Should the body and the bristles of toothbrushes be made of the same material? Why or why not?
Ans.The handle and the bristles of the toothbrush should not be made of the same material as the handle should be hard to give a smooth grip and bristle should be soft and lightweight so that it doesn’t harm the gum of the teeth.

18. Manufacturing of synthetic fibres is actually helping the conservation of forests. Comment on this statement.
Ans. – Natural fibers like cotton and jute are obtained from plants while synthetic fibres are prepared from petrochemicals.So to make synthetic fibre,there is no need to cut plants. Thus we can say that manufacturing of synthetic fibres is actually helping the conservation of forests.

19. List the advantages of plastics over metals.
Ans.
  • Plastics are poor conductors of heat and electricity.
  • Plastics do not react with water and air and thus, do not corrode easily like iron or other metals.
  • Plastics do not react with most of the chemicals.Hence,plastic containers are used for the storage of many chemicals and food items.

20. Which property of plastics makes them versatile but also makes them a major threat to the environment?
Ans. – Plastics cannot be decomposed through natural processes.This property of plastics makes them versatile.Plastics are non-biodegradable and they accumulate in the environment and stay there.This pollutes the environment and makes them a major threat to the environment.

 

 

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