\n5. E.g., Polyethylene.<\/td>\n | 5. E.g., Bakelite, epoxy.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Question 7. \nExplain why the following are made up of thermosetting plastics. \na. Saucepan handles \nb. Electric plugs\/switches\/plugboards \nAnswer: \na. Thermosetting plastic is fire-resistant and can withstand very high temperatures. Due to this, saucepan handles are made up of thermosetting plastic. Such handles do not heat up during cooking,<\/p>\n b. Thermosetting plastic is a bad conductor of electricity and heat. Hence, electric plugs, switches and plugboards are made up of thermosetting plastic.<\/p>\n Question 8. \nCategorise the materials of the following products into \u2018can be recycled’ and \u2018cannot be recycled\u2019: \nTelephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches. \nAnswer:<\/p>\n \n- Can be recycled: plastic toys, ballpoint pens, plastic bowls, plastic chairs, carry bags, plastic covering on electrical wires.<\/li>\n
- Cannot be recycled: Cooker handles, telephone instruments, electrical switches.<\/li>\n<\/ul>\n
Question 9. \nRana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason. \nAnswer: \nA shirt made from synthetic materials does not allow air to pass through it. On the other hand, a shirt made from cotton allows air to pass through it. Also, water from cotton evaporates easily, causing a cooling effect while a synthetic fibre retains moisture leading to humidity in summers. Hence, a cotton shirt keeps the body temperature lower. Hence, a cotton shirt is more comfortable in summers than a shirt made from synthetic material. Therefore, Rana should buy a cotton shirt.<\/p>\n Question 10. \nGive examples to show that plastics are non-corrosive in nature. \nAnswer: \nWe know that acids and bases are corrosive in nature. Nowadays, many acids and bases are stored in plastic containers. This is possible because of non-corrosive nature of plastic. A plastic chair does not get rusted like an iron chair does. This also happens because of the non-corrosive nature of plastic.<\/p>\n Question 11. \nShould the handle and bristles of a toothbrush be made of the same material? Explain your answer. \nAnswer: \nPurpose of the handle of a toothbrush is different from the purpose of bristles of the toothbrush. The handle needs to be strong and less flexible. The bristles need to be highly flexible, soft yet durable. Hence, bristles need to be made up of a different material than the material of toothbrush handle.<\/p>\n Question 12. \n\u2018Avoid plastics as far as possible\u2019. Comment on this advice. \nAnswer: \nWe know that plastic is non-biodegradable. This means that plastic waste keeps getting accumulated in our environment. Accumulation of plastic waste is creating a huge problem for us. Hence, we should avoid plastic as far as possible. We should switch over to biodegradable alternatives wherever possible. For example, we should use shopping bags made up of jute or cloth instead of plastic. If plastic is burnt it releases poisonous gases and the plastic bags thrown in the garbage dump are swallowed by animals. They choke their respiratory system and this causes fatalities in animals.<\/p>\n <\/p>\n Question 13. \nMatch the terms of column A correctly with the phrases given in column B.<\/p>\n \n\n\nA<\/td>\n | B<\/td>\n<\/tr>\n | \n(i) Polyester<\/td>\n | (a) Prepared by using wood pulp<\/td>\n<\/tr>\n | \n(ii) Teflon<\/td>\n | (b) Used for making parachutes and stockings<\/td>\n<\/tr>\n | \n(iii) Rayon<\/td>\n | (c) Used to make non-stick cookwares<\/td>\n<\/tr>\n | \n(iv) Nylon<\/td>\n | (d) Fabrics do not wrinkle easily<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Answer: \n(i) \u2192 (d), \n(ii) \u2192 (c), \n(iii) \u2192 (a), \n(iv) \u2192 (b)<\/p>\n Question 14. \n\u2018Manufacturing synthetic fibres is actually helping conservation of forests\u2019. Comment. \nAnswer: \nSynthetic fibres have replaced natural fibres for most uses. It has resulted in reducing our dependency on natural fibres. Many natural fibres come from plants and hence plants need to be cut down to obtain these fibres. Less demand for natural fibres means there is a reduced need to cut down the trees. It has helped in conservation of forests. Hence, it can be said that manufacturing synthetic fibres is actually helping conservation of forests.<\/p>\n Question 15. \nDescribe an activity to show that thermoplastic is a poor conductor of electricity. \nAnswer: \nFor this, take a small piece of thermoplastic, some copper wires, two electric cells and an electric bulb (from torch).<\/p>\n \n- Connect the bulb with the battery and attach the thermosetting plastic to wires to make a circuit.<\/li>\n
- It is observed that the bulb does not glow.<\/li>\n
- When thermosetting plastic is replaced with a metal rod in the circuit, the bulb begins to glow.<\/li>\n
- This shows that thermosetting plastic is a poor conductor of electricity.<\/li>\n<\/ul>\n
Caution: Do this activity in the presence of your teacher or parent.<\/p>\n NCERT Extended Learning Activities and Projects<\/span><\/p>\nQuestion 1. \nHave you heard of the campaign: \u201cSay No to Plastics\u201d. Coin a few more slogans of this kind. There are certain governmental and non-governmental organisations who educate general public on how to make a wise use of plastics and develop environment friendly habits. \nFind out organisations in your area which are carrying out awareness programmes. If there is none, form one. \nHint. \nRelated slogans: \na. \u201cDon\u2019t laminate the earth!\u201d \nb. \u201cEating plastic, animals died; seeing plastic, nature cried. So, say no to plastics!\u201d \nc. \u201cPlastics are dangerous which spoil the river. After some days we will shiver.\u201d<\/p>\n There are many organisations which carry out awareness programmes such as Bharat Seva Sangh [established in 2000], Sewak (established in 1998), Aarti (established in 2009), MUSS (Manav Uthhan Seva Sansthan) (established in 2001).<\/p>\n <\/p>\n Question 2. \nOrganise a debate in the school. Children may be given an option to role play as manufacturers of synthetic fabrics or those of fabrics from natural sources. They can then debate on the topic \u2018My Fabric is Superior\u2019. \nHint. \nThe clothes which we wear are made up of fabrics. Fabrics are made from fibres obtained from natural or artificial sources. Fibres are obtained from four main sources: animal (wool, silk), plant (cotton, flax, jute), mineral (asbestos, glass fibre) and synthetic (nylon, polyester, acrylic). Fibres are also used for making a large variety of household articles.<\/p>\n Question 3. \nVisit five families in your neighbourhood and enquire about the kind of clothes they use, the reason for their choice and advantages of using them in terms of cost, durability and maintenance. Make a short report and submit it to your teacher. \nHint: \nDo it yourself.<\/p>\n Question 4. \nDevise an activity to show that organic waste is biodegradable while plastic is not. \nHint: \nActivity: Collect garbage from your house before it is thrown into the dustbin. Separate the garbage into two groups.<\/p>\n In group 1, include wastes such as polythene bags, chips packets, empty plastic bottles, plastic toys, etc. In group 2, include only kitchen wastes like peels of fruits and vegetables, waste food, newspaper and garden wastes like dead leaves and other plant parts. Bury these materials separately in two pots and label them as A and B. Remove the top soil after one week and check the status of the garbage. Then approximately after four weeks, check the condition of the garbage again.<\/p>\n It will be observed that the waste in pot B decomposes, while the waste in pot A does not decompose.<\/p>\n This shows that the waste (plastic) kept in pot A is non-biodegradable, while the waste (organic waste) kept in pot B is biodegradable.<\/p>\n Activity 1<\/span><\/p>\nObjective: To show that the nylon thread is stronger than cotton, wool, silk and polyester threads. \nMaterials Required: Different threads (cotton, wool, silk, nylon and polyester), iron stand and pan. \nProcedure:<\/p>\n \n- Take an iron stand with clamp.<\/li>\n
- Take a cotton thread of about 60 cm length.<\/li>\n
- Tie it to the clamp so that it hangs freely from it as shown in the figure.<\/li>\n
- At the free end, suspend the pan so that weight can be placed on it.<\/li>\n
- Add weight one by one till the thread breaks.<\/li>\n
- Note down the total weight required to break the thread. This weight indicates the strength of the fibre.<\/li>\n
- Repeat the same activity with threads of wool, silk, polyester and nylon.<\/li>\n<\/ul>\n
\nObservation: It can be observed that more weight is required to break the nylon thread in comparison to wool, silk, cotton and polyester threads. \nConclusion: Nylon thread is stronger than any other thread.<\/p>\n
i. Polyester: Polyester is made up of repeating units of a chemical called ester. The fibres of polyester do not get wrinkled easily, remain crisp and easy to wash. They are used for making clothes, curtains and dress materials. Terylene, when blended with cotton, is called terry cot while with wool it gives terry wool. Clothes made up of such polymers are convenient to use.<\/p>\n PET (Polyethylene terephthalate) is another example of a polyester. It is used for making bottles, utensils, films, wires and many other items. Polyester fabrics do not wrinkle easily and are easy to wash. \n \niv. Acrylic: Acrylic resembles wool and hence is also called as synthetic wool. It is cheaper and more durable than wool and is easier to wash and maintain.<\/p>\n Characteristics of Synthetic Fibres<\/p>\n \n- Synthetic fibres are cheaper, stronger and more durable than natural fibres.<\/li>\n
- These are easy to maintain, easy to wash, dry up in less time and readily available.<\/li>\n
- These fibres possess unique characteristics which make them popular dress materials.<\/li>\n<\/ul>\n
<\/p>\n Activity 2<\/span><\/p>\nObjective: To study and compare the water absorbing property of natural and synthetic fibres. \nMaterials Required: Two types of cloth (cotton and polyester), water, and mug. \nProcedure:<\/p>\n \n- Soak the two cloth pieces in different mugs containing same amount of water.<\/li>\n
- Now, take out the cloth pieces after five minutes and spread them in the Sun.<\/li>\n
- Compare the amounts of water remaining in the mugs.<\/li>\n
- Also compare the dryness of both the cloth pieces after keeping in Sun for a few minutes.<\/li>\n<\/ul>\n
Observation: It can be observed that the cotton cloth absorbs more water than the polyester cloth. Also, polyester dries up quickly but cotton does not. \nConclusion: Synthetic libres absorb much less water than the natural fibres.<\/p>\n Plastics: Plastic too is a polymer. However, arrangement of units is different in different types of plastics. In some plastics, the individual units are linked in a linear fashion. In some other plastics, the individual units are cross-linked. Plastic is easily moutdable, recyclable, reusable, colourable, can be melted, rolled into sheets or drawn into wires. \n<\/p>\n (b) Cross-linked arrangement of units: \nPlastic is used in making toys, suitcase, bags, cabinets, brush, chairs, tables and many other countless items. Polythene (Poly + ethene) is one of the most famous examples of plastic, which is used in the manufacturing of carry bags.<\/p>\n Plastics as Materials of Choice: Due to various qualities, plastics are used in our everyday life.<\/p>\n \n- Plastic is non-reactive: Plastics do not react with water and air due to which they do not get rusted like iron. They are not corroded easily. So, they are used to store various kinds of materials, including many chemicals.<\/li>\n
- Plastic is light, strong, cheaper and durable: They are generally cheaper than metals. Hence, they are widely used in industry and household articles.<\/li>\n
- Plastic is a poor conductor of heat: Plastics are poor conductors of heat. They are therefore used in making handles of screwdrivers and cooking vessels and in making containers for microwave oven.<\/li>\n
- Plastic is poor conductor of electricity: Plastics are poor conductors of electricity and are used in making a cover for electric wires, cables and appliances. Electric switches are made from bakelite.<\/li>\n<\/ul>\n
Plastic and the Environment: \ni. Biodegradable: A material which can be decomposed by microbes is called a biodegradable material, e.g., jute, cotton, paper, leftover food, etc. \nii. Non-biodegradable: A material which cannot be decomposed by microbes is called a non-biodegradable material, e.g., plastic, iron, copper, etc.<\/p>\n Plastics take several years to decompose, thus cause environmental pollution. \nBurning of synthetic materials releases lots of poisonous fumes into the atmosphere causing air pollution. So, plastics and synthetic fibres are not environment-friendly. \n<\/p>\n Nuisance of Plastic Bags<\/p>\n \n- Plastic bag keeps on accumulating in the environment.<\/li>\n
- It chokes drains leading to waterlogging.<\/li>\n
- A stray animal can die if it accidentally swallows a plastic bag.<\/li>\n<\/ul>\n
How to tackle the problem of plastic waste?<\/p>\n i. Avoid the use of plastics as far as possible. \nii. Follow the 5R principle i.e., Reduce, Reuse, Recycle, Recover and Refuse. \nRecycle \n \niii. Use recyclable plastic or use shopping bags of cloth or jute. \niv. Do not throw plastic bags on roads or in drains. \nv. Reuse plastic containers for keeping household items.<\/p>\n Class 8 Science Chapter 3 Synthetic Fibres and Plastics Additional Important Questions and Answers<\/h3>\nVery Short Answer Type Questions<\/span><\/p>\nQuestion 1. \nWhat are natural fibres? Give examples. \nAnswer: \nThe fibres obtained from plants and animals are called natural fibers. For example cotton, silk, jute, etc.<\/p>\n Question 2. \nDefine polymer. \nAnswer: \nA polymer is a large molecule formed by the combination of many small molecules, each of which is called a monomer.<\/p>\n Question 3. \nName a natural polymer. \nAnswer: \nCellulose.<\/p>\n <\/p>\n Question 4. \nWhat are the monomer units of cellulose? \nAnswer: \nCellulose is made up of a large number of glucose units.<\/p>\n Question 5. \nName the fibre having properties similar to that of silk. \nAnswer: \nRayon.<\/p>\n Question 6. \nWhat is polyester? \nAnswer: \nThe polymer made up of the repeating units of ester is called polyester.<\/p>\n Question 7. \nWhat is the full form of PET? \nAnswer: \nPolyethylene terephthalate.<\/p>\n Question 8. \nWhat is the full form of PVC? \nAnswer: \nPolyvinyl chloride.<\/p>\n Question 9. \nWhat are plastics? \nAnswer: \nThe plastics are a mouldable synthetic material made from a wide range of organic polymers such as polyethylene, PVC, nylon, etc.<\/p>\n Question 10. \nWhat are the two types of arrangement of units in plastic? \nAnswer: \nLinear linking and cross-linking.<\/p>\n <\/p>\n Question 11. \nWhich synthetic fibre is also known as \u2018artificial wool\u2019? \nAnswer: \nAcrylic.<\/p>\n Question 12. \nWhy is teflon used as a tape for sealing purposes? \nAnswer: \nBecause of its toughness, teflon is used as a tape for sealing purposes.<\/p>\n Question 13. \nName the first fully synthetic fibre. \nAnswer: \nNylon.<\/p>\n Question 14. \nWhy is nylon used for making parachutes? \nAnswer: \nNylon is used for making parachutes because it is very strong, elastic and light.<\/p>\n Question 15. \nWhat are petrochemicals? \nAnswer: \nPetrochemicals are the raw materials which are further used to make synthetic fibres.<\/p>\n Short Answer Type Questions<\/span><\/p>\nQuestion 1. \nHow can polythene carry bags be harmful for animals? \nAnswer: \nPolythene carry bags are thrown here and there after being used. Stray cattle consume them. In this case, it can choke their respiratory system and damage their stomach. It can even cause their death.<\/p>\n Question 2. \nGive two disadvantages of synthetic fibres. \nAnswer:<\/p>\n \n- Most synthetic fibers catch fire very easily. Therefore, it is not advisable to wear them near a source of fire,<\/li>\n
- Most synthetic fibers absorb very little moisture. They become sticky when the body sweats, which makes them uncomfortable to wear in hot weather.<\/li>\n<\/ol>\n
<\/p>\n Question 3. \nWrite a short note on acrylic. \nAnswer: \nAcrylic resembles wool and hence is also called synthetic wool. It is cheaper and more durable than wool and is easier to wash and maintain. Acrylic is less expensive and easily available.<\/p>\n Question 4. \nWhat is the difference between nylon and rayon? \nAnswer:<\/p>\n \n\n\nRayon<\/td>\n | Nylon<\/td>\n<\/tr>\n | \n1. It was the first synthetic fibre.<\/td>\n | 1. It was the first truly synthetic fibre.<\/td>\n<\/tr>\n | \n2. Rayon is made from wood pulp.<\/td>\n | 2. Nylon is made from coal, water and air.<\/td>\n<\/tr>\n | \n3. Rayon is used for making curtains, bedsheets, etc.<\/td>\n | 3. Nylon is used for making socks, ropes, toothbrushes, parachutes, etc.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Question 5. \nWhat do you mean by biodegradable and non-biodegradable materials? Explain with examples. \nAnswer:<\/p>\n | | |