Lakhmir Singh & Manjit Kaur: Synthetic Fibers And Plastics- 2 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.21. Arrange the following fibres in the order of increasing strength (keeping the fibre of least strength first): Nylon, Cotton, Wool, Polyester, Silk

Some fibres are stronger than the others. The fibres are arranged in terms of strength in the following way: Wool, Cotton, Polyester, Nylon, Silk.
Silk is the strongest fibre whereas wool is the weakest in terms of strength.

Q.22. What is PET? State the uses of PET.

PET is a form of polyester. Polyester is the synthetic fibre which is made up of repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell. PET is used for making bottles, utensils, films and wires.

Q.23. What is acrylic? State one important property of acrylic.

Acrylic is a synthetic fibre which appears to resemble wool. It is flexible, resistant to moth, oil and chemicals. The clothes made from acrylic are relatively cheap and are available in a variety of colours.

Q.24. Write the uses of acrylic fibres.

Acrylic is a synthetic fibre which appears to resemble wool. It is flexible, resistant to moth, oil and chemicals. It is used in the following ways:

• It is used for making sweaters and tracksuits and also for the linings of boots and gloves.
• It is also used in making furnishing fabrics and carpets.
• It can also be used to make fur and many different knitted clothes.

Q.25. Why should we not wear clothes made of synthetic fibres (like nylon or polyester) while working in the kitchen?

Synthetic fibres such as nylon or polyester are different from the natural fibres. They melt on heating. If the clothes made of synthetic fibres catch fire, it can be very dangerous. The fabric will melt and can stick to the body of the person wearing it. Hence, we should not wear synthetic clothes while working in a kitchen or working in a laboratory.

Q.26. What type of shirts should we buy for summer: cotton shirts or shirts made from synthetic materials (like polyester)? Give reason for your answer.

We should buy cotton shirts to wear in summers. This is because cotton absorbs sweat from our body and allows it to evaporate into the air. It also discourages the growth of bacteria and does not cause any skin allergies.

Q.27. Explain how, manufacturing of synthetic fibres is actually helping in the conservation of forests.

The raw materials for natural fibres are mainly derived from plants and animals. It requires the cutting of a lot of trees which leads to deforestation. On the other hand, the raw materials for synthetic fibres are mainly petrochemicals such as coal. Hence, the manufacturing of synthetic fibres helps in the conservation of forests.

Q.28. What are plastics? Name any five commonly used articles made of plastics.

Plastic is a polymer like a synthetic fibre. The arrangement of units in a plastic can be linear or cross-linked. Plastic articles are available in all possible shapes and sizes. It can be easily moldable and can be shaped in any form. It can be recycled, reused, coloured, melted and can be rolled into sheets or made into wires. Plastic is used to manufacture toys, combs, containers, utensils and electrical switches.

Q.29. What are the various types of plastics? Give two examples of each type of plastics.

Plastic is a polymer like a synthetic fibre. The arrangement of units in a plastic can be linear or cross-linked. Based on the arrangement of monomers, plastics are of the following types:

Thermoplastics: The plastics which gets deformed easily on heating and can be bent easily are called thermoplastics. For example, polythene and PVC are thermoplastics. These are used in the manufacturing of toys, combs and different types of containers.

Thermosetting plastics: The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics. For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils. Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. It is used to make floor tiles, kitchenware and fire resistant fabrics.

Q.30. Why are thermoplastics not used for making frying pan handles?

Thermoplastics gets deformed easily on heating and can also be bent easily. As a result, they are not used for making frying pan handles. Frying pan handles are made with thermosetting plastics which are resistant to fire and can tolerate heat better than other plastics.

Q.31. Explain why, frying pan handles are made of thermosetting plastics.

Frying pan handles are made with thermosetting plastics which are resistant to fire and can tolerate heat better than other plastics. For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity.

Q.32. Why are electric witches, plugs and sockets made of thermosetting plastics?

The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics. For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils. Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. Hence, electric witches, plugs and sockets made of thermosetting plastics.

Q.33. Explain the difference between thermoplastics and thermosetting plastics.

Thermoplastics: The plastics which gets deformed easily on heating and can be bent easily are called thermoplastics. For example, polythene and PVC are thermoplastics. These are used in the manufacturing of toys, combs and different types of containers.

Thermosetting plastics: The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics. For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils. Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. It is used to make floor tiles, kitchenware and fire resistant fabrics.

Q.34. Should the handle and bristles of a toothbrush be made of the same type of plastic material? Explain your Answer.

The handle and bristles of a toothbrush should be made of different type of plastic material. The handle of toothbrush should be hard and strong whereas the bristles should be soft and flexible.

Thus, the handle is made of plastic while the bristles are made of nylon.

Q.35. Explain why, plastic containers are preferred for storing food.

Plastic is a polymer like a synthetic fibre. The arrangement of units in a plastic can be linear or cross-linked. Plastic containers are preferred for storing food because of the following reasons:

• Plastic is non-reactive. It does not react with water and air. It is therefore, safe to keep food in plastic containers.
• Plastic is light, strong and durable and can be moulded into different shapes and sizes. It is cheaper than metals. It is widely used in making household items including food containers.
• Plastics are poor conductors of heat and electricity and can be used for making handles of frying pans.

Q.36. Choose the thermoplastics and thermosetting plastics from the following: Melamine, Polythene, Bakelite, Polyvinyl chloride

Melamine and Bakelite are thermosetting plastics. The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics. For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils. Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. It is used to make floor tiles, kitchenware and fire resistant fabrics.

Polythene and poly vinyl chloride are thermoplastics. The plastics which gets deformed easily on heating and can be bent easily are called thermoplastics. For example, polythene and PVC are thermoplastics. These are used in the manufacturing of toys, combs and different types of containers.

Q.37. State two uses of polythene.

Polythene is a thermoplastic. It is used in the manufacturing of toys, combs and different types of containers.

Q.38. Write the full form of PVC. Is it thermoplastic or thermosetting plastic?

The full form of PVC is polyvinyl chloride. PVC is a thermoplastic. The plastics which gets deformed easily on heating and can be bent easily are called thermoplastics.

Q.39. Write two uses of Bakelite.

Bakelite is a thermosetting plastic. The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics. For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils.

Q.40. State two uses of melamine.

Melamine is a thermosetting plastic. The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics. Melamine is a thermosetting plastic which is resistant to fire and can tolerate heat better than other plastics. It is used to make floor tiles, kitchenware and fire resistant fabrics.

Q.41. Give two uses of PVC.

The full form of PVC is polyvinyl chloride. PVC is a thermoplastic. The plastics which gets deformed easily on heating and can be bent easily are called thermoplastics. It is used in the manufacturing of toys, combs and different types of containers.

Q.42. Write some of the uses of plastics in healthcare industry.

Modern healthcare would not be possible without the use of plastic materials. Plastics can be used in healthcare in the following ways:

• Plastics are used in the packaging of tablets, syringes, doctor’s gloves and a number of medical instruments.
• Threads used for stitching wounds are made of medical instruments.
• Plastics are used for making intravenous blood bags and heart valves as well.

Q.43. Classify the following as biodegradable and non-biodegradable materials: Woollen clothes, Polythene bags, Paper, Aluminium cans, Toothbrush, Peels of vegetables and fruits, Cotton cloth, Jute bag, Electric switch, Frying pan handle.

A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable. Following are the biodegradable materials:
Woollen clothes, paper, peels of vegetables and fruits, Cotton cloth and Jute bag.
A material which is not easily decomposed by natural processes is termed as non-biodegradable. Following are the non-biodegradable materials:
Polythene bags, Aluminium cans, Toothbrush, Electric switch and Frying pan handle.

Q.44. State whether plastic is biodegradable or non-biodegradable? Give reasons.

Plastic is non-biodegradable. It takes several years for plastic to decompose and it is not environment friendly. It causes environmental pollution. Also, the burning process of synthetic material is quite slow. It does not get completely burnt easily. It releases lots of poisonous fumes into the atmosphere when burned and causes air pollution.

Q.45. Explain how, the use of plastics has a bad effect on the environment.

The use of plastic has a bad effect on the environment because it is non-biodegradable. It takes several years for plastic to decompose and it is not environment friendly. It causes environmental pollution. Also, the burning process of synthetic material is quite slow and it does not get completely burnt easily. It releases lots of poisonous fumes into the atmosphere when burned and causes air pollution.

Q.46. Explain why, the disposal of plastic wastes is a major problem. Give two reasons only.

The disposal of plastic wastes is a major problem because of the following reasons:

• Plastic is non-biodegradable. It takes several years for plastic to decompose and it is not environment-friendly.
  It causes environmental pollution.
• The disposal of plastic wastes is a major problem. Plastics cannot be burnt because they release poisonous gases.
• Plastic bags thrown in the garbage can be swallowed by the animals such as cows. It can result in choking their respiratory system and can be fatal. Therefore, we must avoid the use of plastic as much as possible.

Q.47. What are the various ways to save the environment from excessive plastic wastes?

Plastic is non-biodegradable. It takes several years for plastic to decompose and it is not environment friendly. It causes environmental pollution. Following are the ways to save the environment from excessive plastic wastes:

• We must try to Reduce, Reuse, Recycle and recover the use of plastic items. We must develop the habits which are environment friendly.
• We must not throw plastic in the water bodies or on the roads.
• We must take a cotton carry bag or a jute bag while shopping.
• We must try to minimize the use of plastic materials. For example, we must use a steel lunch box or steel containers instead of plastic ones.

Q.48. How do carelessly thrown plastic bags (polythene bags) affect:
(a) dirty water drains and sewers?
(b) animals (such as cows)?

(a) Plastic is non-biodegradable. It takes several years for plastic to decompose. When thrown in the water drains or in sewers it results in choking of the drains. Therefore, we must avoid the use of plastic as much as possible.

(b) Plastic bags thrown in the garbage can be swallowed by the animals such as cows. It can result in choking their respiratory system and can be fatal. Therefore, we must avoid the use of plastic as much as possible.

Q.49. What is meant by the 3R’s principle in the context of use of plastics?

3R’s principle in the context of use of plastics means we must try to Reduce, Reuse and Recycle the use of plastic items. We must develop the habits which are environment-friendly. In order to achieve this, we must not throw plastic in the water bodies or on the roads. We must take a cotton carry bag or a jute bag while shopping. We must try to minimize the use of plastic materials. For example, we must use a steel lunch box or steel containers instead of plastic ones.

Q.50. State the various ways in which we can avoid (or minimize) the use of plastics.

We must try to Reduce, Reuse, Recycle and recover the use of plastic items. We must develop the habits which are environment friendly. In order to achieve this, we must try to do the following:

• We must take a cotton carry bag or a jute bag while shopping.
• We must try to minimize the use of plastic materials. For example, we must use a steel lunch box or steel containers instead of plastic ones.
• We must not throw plastic in the water bodies or on the roads.