NCERT solution for class 8 // Science // Chapter 3 - Synthetic fibres and plastics

 NCERT solutions > class 8 >  science > Chapter 3

NCERT solution for class 8 // Science  // Chapter 3 -  Synthetic fibres and plastics


Chapter 3 -  Synthetic fibres and plastics

Q1. Explain why some fibres are called synthetic

Ans - The fibres which are prepared by man by using chemicals are called synthetic fibre these are made by the joining of small units called monomer to form a long chain of polymer 

Example  - Rayon, Nylon, Acrylic, Polyester etc are the synthetic fibres

Q2. Mark the correct answer

Rayon is different from synthetic fibres because 

a) It has a silk like appearance

b) It is obtained from wood pulp

c) Its fibre can also be woven like those of natural fibres 

Ans  - It is obtained from wood pulp


Q3. Fill in the blanks with appropriate words

a) Synthetic fibres are also called artificial or man made fibres 

b) Synthetic fibres are synthesized from raw material called petrochemicals

c) Like synthetic fibres plastic is also a polymer

Q4. Give examples which indicate that nylon fibres are very strong

Ans - Nylon fibres are very strong  so it is used for making ropes which are used for climbing rocks and making parachutes due to its high tensile strength

Q5 . Explain why plastic containers are favoured for strong food?

Ans- Plastic containers are favoured for strong food due to showing following properties 

  • Lightweight 
  • good strength 
  • lower price 
  • easy handling

Q6. Explain the difference between thermoplastic and thermosetting plastics.

Ans- 

 

Thermoplastic

Thermosetting Plastic

1

 

These plastic becomes soft on heating and can be molded any shape Which become  permanent set on cooling

1.    These plastic can not be molded again

 

2.

 

They do not looses their plasticity on heating and cooling repeated

2.    They looses their property on heating

 

 

3

Eg. Polyethylene ,Nylon , Plastic , PVC

3       Eg. Bakelite , Melamine

4

They are used to make toys , pipes , containers , combs etc

 

4       They are used to make Electrical switches and plug , crockery, table tops

 

Q7 . Explain why the following are made from thermosetting plastics  

 a) Saucepan handles 

 b) Electric plugs /switches / plug boards 

Ans- a) Saucepan handles are made of thermosetting plastic because these plastic do not get soften on heating and these are poor conductor of heat 

b ) Electric plugs  /switches and plug boards are made up of thermosetting plastic because it is a poor conductor of heat and electricity

Q8 . Categorize the material of the following products into can be recycled and cannot be recycled

Telephone instrument, plastic toys ,cooker handles ,carry bags, ballpoint pen ,plastic balls , plastic covering on electrical wires , plastic chairs , electrical switches 

Ans- 

Cannot be recycled - 

  • Telephone instruments 
  • Cooker handles 
  • Electrical switches 

Can be recycled

  • Plastic toys 
  • Plastic chairs
  •  Carry bags 
  • Plastic covering on electrical wires 
  • Ball point pens
  •  Plastic balls

Q9 . Rana wants to buy shirts  for summer should He buy cotton shirts or shirts made from synthetic material advice Rana giving your reason 

Ans- Rana should buy shirts made from cotton because cotton is a good absorber of water it absorbs the sweat coming out from the body and expose it to the environment .It feels cooling our body

Q10. Give examples to show that plastics are non corrosive in nature? 

Ans- 

  • Plastics are non reactive with most material so it does not corroded if it come in contact with strong chemicals
  • Plastic don't react with air and water example plastic home appliances
  • Plastic don't react with acid or bases so these are kept in plastic bottles the cleansing chemicals used at home are stored in plastic bottles

Q11. Should the handle and bristles of toothbrushes may be made of the same material explain your answer 

Ans- No ,the handles and bristles of the toothbrushes not made of the same material . The handles of the toothbrushes  are strong and hard and it is made up of plastic while the bristles of brushes are very soft and flexible and they are made from nylon

Q12. Avoid plastics as far as possible comment on your advice. 

Ans- Yes we should avoid plastic as far as possible because plastics are non biodegradable that takes several years to decompose and can cause environmental pollution if they burn . They release poisonous gases plastic bags dump in the garbage are swallowed by the animals like a cow and it causes choking of their respiratory system

Q13. Match the terms of column A correctly with the phrases given in column B 

Column A.                        Column  B 

Polyester           -         prepared by using wood pulp 

Teflons.             -          used for making parachutes 

                                        andstockings 

Rayon.           -          used to make non stick cookware 

Nylon            -           fabric do not wrinkle easily

Ans -

Column A.                        Column  B 

Polyester         -         Fabric do not wrinkle easily

Teflons.              -              used to make non stick cookware 

Rayon.            -         prepared by using wood pulp 

Nylon             -          used for making parachutes 

                                        andstockings 


Q14. Manufacturing synthetic fibres is actually helping conservation of forest comment ?

Ans- Synthetic fibres are made up of petrochemicals while the natural fibre are made up of plants and for the natural fibres preparation so many plants are cutting down it leads to deforestation show the manufacturing of synthetic fibres is actually helping the conservation of forest

Q15. Describe an activity to show that thermoplastic is a poor conductor of electricity

Ans- Requirment 

Bulb, wires ,a battery, a piece of metal ,and a plastic pipe

Arrange the all things are shown in figure 

Procedure 

Set up all the things as shown in figure after that switch on and current is passed from the wire you will observe that the bulb glow in the first case in the second case the bulb does not glow hence the plastic pipe is shown in a second figure is a poor conductor of electricity while the metal shows in the first figure is a good conductor of electricity

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