CBSE- Synthetic Fibres and Plastics-NCERT Solutions


            



NCERT SOLUTIONS
Synthetic Fibres and Plastics
1.  Explain why some fabrics are called synthetics.
       Ans. Some fabrics do not occur in the nature are hence called synthetic fibres.
2.  Rayon is different from synthetic fibres because:
           •  It has a silk like appearance.
           •  It is obtained from wood pulp.
           •  Its fibres can also be woven like those of natural fibres.
           •  It is obtained from wood pulp.
       Ans. It is obtained from wood pulp
3.  Fill in the blanks with appropriate word:
           a)  Synthetic fibres are also called man-made or artificial fibres.
           b)  Synthetic fibres are synthesized from raw-materials called petrochemicals.
           c)  Like synthic fibres, plastic is also a polymer.

4.  Give examples which indicate that nylon fibres are very strong.
       Ans. Nylon fibres are very strong so they are used for making parachutes and ropes for rock-climbing.
5.  Explain why plastic containers are favored for storing food?
       Ans. Plastics do not react with food items and they are strong, light and durable. Hence they are favored for storing food.
6.  Explain the differences between thermoplastics and thermosetting plastics.
       Ans. Differences:
Thermoplastics Thermosetting plastics
1.  These are the plastics that can be deformed easily on heating and can bend also.
2.  They are used for manufacturing cars, toys and containers.		 1.  These are the plastics that cannot be softened by heating once they are moulded.
2.  Bakelites are used for making electrical switches, handles for various utensils etc.
7.  Explain why the following are made of thermosetting plastics.
 I.  Saucepan handles
II.  Electric plugs/ switches/ switch boards
       Ans. (a) the handles of a saucepan are made of thermosetting plastic because it is a bad conductor of heat and does not get heated up while cooking.
                  (b) Electric plugs/ switches/ plug boards are saucepan is made of thermosetting plastic because it is a bad conductor of electricity. The electric current does not pass through such plastics.
8.  Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’. Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastics bowls, plastics covering on electrical wires, plastics chairs, and electrical switches.
       Ans. Recyclable: Toys, carry boys, cooker handles, ball point pen, plastic chairs, electric wire Rest can’t be recycled.
9.  Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Give reasons for your suggestion.
       Ans. Rana should buy cotton shirts for summer because cotton is a poor conductor of heat. It does not transmit heat to and from the body and protects us from heat. Cotton is more capable of holding absorbing sweat than synthetic clothes keeping us cool.
10.  Give examples to show that plastics are non corrosive in nature.
       Ans. Plastics are non corrosive in nature as they do not react with any substance and do not show any chemical change.
11.  Should the handle and the bristles of the toothbrush be made of the same material? Why?
       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 so that it doesn’t harm the gum of the teeth.
12.  ‘Avoid plastic as far as possible’. Comment on this.
       Ans. Plastics are non-biodegradable materials and is harmful for our environment. They can’t be finally disposed off and hence should be avoided.
13.  Match the following correctly:
       Ans.   (I)  Polyester- Fabrics don’t wrinkle easily
                   (II)  Teflon- Used to make non-stick cookwares
                   (III)  Rayon- Prepared by using wood pulp
                   (IV)  Nylon- Used for making parachutes and stockings
14.  ‘Manufacturing synthetic fibres is actually a helping conservation of forests’. Comment.
       Ans. Natural fibres require raw materials from plants and animals and they resulted in deforestation and animal killing. However synthetic fibres are made up of synthetic materials and not from plants or animals. Therefore manufacturing synthetic fibres is actually a helping conservation of forests.
15.  Describe an activity to show that thermoplastic is a poor conductor of electricity.
       Ans. Electrical wires have plastic covering which show that plastics are poor conductors. Another example is the handle of a screw driver which is also made of plastic.