Page 1 :
Bakelite isa poor conductor of heat and electricity, It is used for \, , Vill : Science, 3. Synthetic Fibres and Plastics making electrical switches, handles of various utensils etc.,, 1. Explain why some fibres are called synthetic? Melamine is a versatile material. It resists fire and can tolerate, Synthetic fibres are man-made fibres. A synthetic fibre is a chain of heat better than other plastics. It is used for making floor tiles,, small units joined together. Each small unit is actually a chemical kitchenware and fabrics which resist fire., substance. Many such small units combine to forma large single unit . + “i *, called a Polymer. Rayon, Nylon, Terylene, Acrylic are all examples 7. Explain why the following are made of thermosetting plastics., of synthetic fibres. a) Saucepan handles., b) Electric plugs/ switches/ plug boards., 2. Mark the correct answer: Thermosetting plastics are poor conductors of heat and electricity., Rayon is different from synthetic fibres because |, a) it has a silk-like appearance. 8. Categorise the materials of the following products into 'can be, recycled' and 'cannot be recycled’., 3. Fill in the blanks with appropriate words. All thermosetting plastics can be recyled., a) Synthetic fibres are also called man-made or artificial fibres. Recyclable Plastics : Plastic toys, carry bags, cooker, b) Synthetic fibres are synthesised from raw material called handles, plastic chairs, ball point pens, plastic covering on, woodpulp electrical wires, c) Like synthetic fibres, plastic is also a polymer. Non-recyclable plastics : Electrical switches, plastic bowls,, telephone instruments, 4. Give examples which indicate that nylon fibres are very, ng 9. Rana wants to buy shirts for summer. Should he buy cotton, Articles such as socks, ropes, tents, toothbrushes, car seat belts, shirts or shirts made from synthetic material ? Advise Rana,, sleeping bags, curtains are made of nylon. Nylon is also used for EAvInG YUE reason. ;, making parachutes and ropes for rock climbing. A nylon thread is We sweat more in the summer season. Cotton is a strong water, actually stronger than a steel wire. absorber. It helps to absorb the sweat and introduce to the, environment on evaporation. Our body takes out heat as the sweat, 5. Explain why plastic containers are favoured for storing food. evaporates from our body. Therefore our body loses heat and gets, Plastic containers are known for light weight, lower price, good cooled. Hence, Rana should buy cotton shirts for summer., strength and easy handling. Hence we find plastic containers the most . . a., convenient in storing food items, water, milk, pickles, dry food ete., 10 Give examples to show that plastics are noncorrosive in, 2 nature., 6. Explain the difference between thermoplastics and Plastics are non-corrosive in nature, they do not react even if they, | come in contact with strong chemicals. For example, the cleaning, , thermosetting plastics. . : :, oe chemicals that we use at home are stored in plastic bottles, instead, , Plastic which gets deformed easily on heating and can be bent :, easily are known as thermoplastics. Ex : Polythene and PVC used of metal containers., for making combs, t d various types of containers., , eee 11. Should the handle and bristles of a toothbrush be made of the, , Plastics which when moulded once, can not be softened by heating _. : ., are called thermosetting plastics. Ex : Bakelite and melamine. 10 same material ? Explain your answer.
Page 2 :
No, the handle and bristles of a tooth brush should be made of, different materials. The handle of a toothbrush should be hard and, strong, so it should be made from plastic. The bristles should be, soft and flexible, so they should be made from nylon., , 12. ‘Avoid plastics as far as possible'. Comment on this advice., , Plastics are non-biodegradable materials. So use of plastics is harmful for our, environment. The plastics cannot be finally disposed off. Thus, plastics should, be avoided as far as possible., , 13. Match the terms of column A correctly with the phrases given, in column B., , A B, i) Polyester — 4) Fabrics do not wrinkle easily, ii) Teflon — ¢) Used to make non-stickcookwares, iii) Rayon — a) Prepared by using wood pulp, iv) Nylon — ») Used for making parachutes and stockings, , 14. ‘Manufacturing synthetic fibres is actually helping conservation of, forests'. Comment., , Natural fibres come from plants and animals, and therefore production of, more natural fibres would lead to cutting of more trees thus causing, deforestation., , But on the other hand, raw materials of synthetic fibres are mostly, petrochemicals. Therefore, manufacturing synthetic fibres lead to conservation, , of forests., , 15. Describe an activity to show that thermoplastic is a poor, conductor of electricity., , , , For this activity, weneed two conducting wires, a bulb, a battery, a conduct: \, and a thermoplastic., , Case I - When we use a conductor: \, Activity - Connect one terminal of the battery to one end of the conductor *, using a wire and the other end of the conductor to the bulb. Using the other, , wire, connect the other end of the battery to the bulb., Result - We see the bulb plowing which concludes that the conductor is a, , good conductor of electricity since the current flows through it., , Case II - When we use a thermoplastic., , Activity - Connect one terminal of the battery to one end of the thermoplastic, using a wire and and the other end of the thermoplastic to the bulb. Using the, other wire, connect the other end of the battery to the bulb., , Result - We see that the bulb not glowing which concludes that the, , thermoplastic is a poor conductor of electricity since the current ‘does not, , flow through it., , II. Additional Questions and Answers:, , 1. Are polymers Natural or Manmade?, Polymers can be both natural and manmade., Cotton is a natural polymer called cellulose. This cellulose is made of a, number of glucose un{ts. Other examples are wool and silk., Nylon and Rayon are manmade fibres., , 2. What is PET in PET bottles?, PET is also a type of Polyester. It is used to make PET Bottles., Full form of PET is PolyEthylene Terephthalates., , 3. Do all synthetic fibres help in conservation of fores?, Some synthetic fibres are made from petrochemicals., Ex: Nylon, Polyester, Acrylic, No trees are cut to make them. We can say that they help in conservation, of forests, However some synthetic fibres are made from wood pulp., Ex: Rayon, So making rayon requires cutting of trees., , b
Page 3 :
4. Where are plastics commonly used?, , Plastics are used in, * Healthcare industry - In packaging of tablets, threads used for, , stitching wounds, syringes, doctor's gloves and other medical, , instruments., * Plastic cookware in ovens - Special plastic cookware is used in, microwave ovens for cooking food. In microwave ovens, the heat, , cooks the food but does not affect the plastic vessel., * Non-stick cookwares - Teflon is a special plastic on which oil and, water do not stick. It is used for non-stick coating on cookwares., * Fire-proof plastics - Some fireproof plastics like melamine are, available which make them flame resistant. It is commonly used in, , uniforms of firemen., , How to become ‘Fiber-wise'?, It means to use the fiber which cause minimum damage to the, , environment. The following are some of the steps to become ‘fiber-wise', , 1. Use Cotton / Jute Bag for Shopping instead of Plastic Bag, 2. Do not throw plastic on road or in water bodies(rivers), Use minimum amount of plastic(Use steel lunch box in place of, , 3., ay, By, , plastic lunch box), , 12
