3. Synthetic Fibres And Plastics-Additional Questions With Solutions Science Class 8 In English

Additional Questions With Solutions

Que: Write the differences between thermoplastics and thermosetting plastic.

Ans:

Que: What is Bakelite?

Ans: Bakelite is a thermoplastic. It is a polymer which is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc.

Que: What is melamine?

Ans: Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used for making floor tiles, kitchenware and fabrics which resist fire.

Que: Explain why plastic containers are favoured for storing food.

Ans: plastic containers are favoured for storing food. This is because of their light weight, lower price, good strength and easy handling. Being lighter as compared to metal.

Que: Give examples which indicate that nylon fibres are very strong.

Ans: Nylon is also used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.

Que: Why are the handles of screw driver and fry pan made of plastic?

Ans: Because plastics are poor conductors of heat and electricity.

Que: Why is the disposal of a plastic material major problem?

Ans: Toxin produced by plastic is major problem to remove from environment. As on burning it produces toxic smoke and disposal in soil it produce toxic effect. So it can’t be removed easily.

Que: What is biodegradable?

Ans: A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable.

Example: peels of vegetables and fruits, paper, wood , cotton clothes etc.

Que: What is non-biodegradable?

Ans: A material which is not easily decomposed by natural processes is termed as non-biodegradable. For Example: Tin aluminium plastic bags and other metals.

Que: Explain why some fibres are called synthetic.

Ans: Some fibres are called synthetic because they are made by human beings.

Que: Mark the correct answer.

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.

Ans: 

• It is obtained from wood pulp.

Que: Give examples which indicate that nylon fibres are very strong.

Ans: Parachutes and nylon ropes are used for rock climbing.

Que: Name the plastic whose sheets are used for packing liquids.

Ans: Polythene.

Que: Why is teflon used as tape for sealing purpose?

Ans: Becausee of its toughness, teflon is used as tape for sealing purpose.

Que: Name the first fully synthetic fibre.

Ans: Nylon.

Que: Why nylon is used for making parachutes?

Ans: Nylon is used for making parachutes, because it is very strong, elastic and light.

Que: Name the material used for making ropes for rock climbing.

Ans: Nylon.

Que: What is polyester?

Ans: Polyester is made up of the repeating units of an ester.

Que: Name the plastic used for making polythene bags.

Ans: Polythene bag is made of plastic which is a polymer of ethene.

Que: What name is given to plastics which can be re-set a number of times?

Ans: Thermoplastics.

Que: Classify the following into thermosetting and thermoplastics-combs, bakelite, melamine, toys.

Ans: Thermosetting – bakelite, melamine

Thermoplastics – combs, toys

Que: Why are the chemicals in the laboratory stored in plastic containers ?

Ans: Plastics are non-reactive, so they can be used for storing chemicals.

Que: Can you store pickles in plastic containers ? Why ?

Ans: Plastics are non-reactive, so pickles can be stored in them.

Que: Why are the electric wires covered with plastic ?

Ans: Plastic is a poor conductor of electricity, therefore, the wires are covered with it.

Que: Why do we use plastic cookwares in microwave ovens?

Ans: We use plastic cookware in microwave ovens, because they are not affected by heat but the food is cooked.

Que: Tin takes about 100 years to degenerate. Is it biodegradable or non-biodegradable?

Ans: Tin is non-biodegradable.

Que: Is it advisable to use recycled plastic containers for storing food?

Ans: No, we should not use recycled plastic containers for storing food because they contain colouring agents.

Que: As a responsible citizen, what are the 4R’s we should remember?

Ans: Reduce, Reuse, Recycle and Recover.

Que: Aperson has to make a non-stick pan. He has three types of plastic-Bakelite, Teflon and PVC. Which plastic will he use for coating and why?

Ans: The person will use Teflon because it is not affected by heat and does not react chemically with other substances.

Que: Explain the difference between thermoplastic and thermosetting plastics.

Ans: 

Que: Differentiate between natural and synthetic fibres.

Ans: Natural fibres are obtained from nature, e.g., cotton whereas synthetic fibres are made by man, e.g., nylon.

Que: How is rayon made? Give one advantage of using rayon.

Ans: Rayon is obtained from wood pulp by treating it chemically. It is cheaper than silk, but can be woven like silk fibre.

Que: Is nylon fibre so strong, that we can use it to make parachutes ?

Ans: Yes, nylon is very strong and it can be used for making parachutes.

Que: Give some uses of PET.

Ans: PET is used for making bottles, utensils, fibres and wires.

Que: Give the composition of Polycot and Polywool.

Ans: Polycot is a mixture of polyester and cotton, Poly wool is a mixture of polyester and wool.

Que: What properties of plastics make it useful for many things?

Ans: Plastics can be recycled, reused, coloured, melted, rolled into sheets or made into wires, so they are very useful.

Que: Why is melamine used for making kitchenware?

Ans: Melamine resists fire and can tolerate heat better than other plastics. So, it is used for making kitchenware.

Que: Buckets made up of plastics are better. Why?

Ans: Buckets made up of plastic are better because they are light, strong and durable.

Que: Differentiate between biodegradable and non-biodegradable materials.

Ans:

Que: Should the handle and bristles of a tooth brush be made of the same material ? Explain your answer. 

Ans: No, the handle and bristles of tooth brush cannot be made of the same plastic. The handle is hard but the bristles are soft and flexible.

Que: Give three advantages of polythene over natural materials. 

Ans: Three advantages of polythene over natural materials are :

• It is strong but flexible.
• Can be rolled into sheets.
• Water resistant.

Que: Give one use each of bakelite, nylon and acrylic.

Ans: Bakelite is used for making plugs and switches. Nylon is used in textile industry to produce clothes. Acrylic is used as a substitute of natural wool for knitting sweaters, blankets etc.

Que: Fill in the blanks with appropriate words.

1. Synthetic fibres are also called ……….. or ……….

2. Synthetic fibres are synthesised from raw material called …………

3. Like synthetic fibres, plastic is also a …………..

Ans: 

1. artificial, man-made
2. mono or petrochemicals
3. polymers.

Que: Explain why plastic containers are favoured for storing food. 

Ans: Food can be stored in plastic containers because

• Plastics are non-reactive.
• Plastics are light and strong.
• Plastics are durable.

Que: Explain why the following are made of thermosetting plastics: 

1. Saucepan handles

2. Electric plugs/switches/plug boards.

Ans: 

1. Saucepan handles are made of thermosetting plastics because they are bad conductors of heat.

2. Electric plugs/switches/plug boards are made of thermosetting plastics because they are bad conductors of electricity.

Que: 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 cotton shirts. Cotton clothes are preferred in summer because they absorb sweat and the person feels cool whereas synthetic materials do not absorb sweat and the person feels uncomfortable.

Que: Give examples to show that plastics are noncorrosive in nature. 

Ans: 

• Buckets made of iron get rusted but those made of plastic are not rusted.
• Food can be stored in plastic containers, as they are resistant to chemicals in the food
• Teflon coated pans are used instead of metallic as it doesnot react with chemicals in the food.

Que: Give three advantages of rayon.

Ans: Advantages of rayon are :

• It is cheap.
• It can be dyed in many colours.
• It can be woven like silk.

Que: What are the advantages of nylon?

Ans: Nylon fibre is strong, elastic and light. It is lustrous and easy to wash.

Que: Give some uses of nylon.

Ans: Nylon can be used for making socks, ropes, tents, toothbrushes, sleeping bags, curtains, parachutes and ropes for rock climbing.

Que: What are the advantages of using fabrics made of polyester?

Ans: Fabrics made of polyester

• do not get wrinkled easily
• are easy to wash,
• easy to maintain.

Que: Why people prefer to wear acrylic sweaters than pure wool sweaters?

Ans: Acrylic sweaters are cheaper and easy to maintain. They are available in many colours.

Que: What are the disadvantages of wearing synthetic fabrics?

Ans: Synthetic fabric catches fire very easily. It melts and sticks to the body of the person wearing it. During summers, synthetic fibres do not absorb sweat and a person wearing it feels uncomfortable.

Que: Give the characteristics of synthetic fibres.

Ans: Synthetic fibres dry up soon, are durable, less expensive, readily available and easy to maintain.

Que: 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, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Ans: 

Que: Match the terms of Column A correctly with the phrases given in Column B. 

Ans:

Que: ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Ans: The said statement is correct to a certain extent. The forests would be conserved if synthetic fibres are used, but other effects of synthetic fibres are more harmful. Disposal of synthetic fibres causes lot of environmental pollution. When synthetic fibres bum, lot of smoke is produced.

Que: ‘Avoid plastics as far as possible’. Comment on this advice.

Ans: Plastics are very useful, but it causes serious environmental and health concern :

• Plastics are non-biodegradable.
• Careless disposal of plastic bags, chokes, drains and blocks the soil.
• If eaten by cows, it can kill them.
• Plastic bags can also contaminate foodstuffs due to poisonous dyes getting absorbed into food

Que: How is plastic useful in healthcare industry?

Ans: In healthcare, plastics are used

• for packaging of tablets
• as threads for stitching wounds
• in syringes
• doctor gloves
• for making a number of medical instruments.

Que: “Even though plastics are very useful, they are not environment friendly.” Justify the statement.

Ans: Plastics are very useful, but their disposal is a big problem. Plastics are non-biodegradable and take many years to decompose. They release a lot of poisonous fumes, when burnt so they cause environmental pollution.

Que: Give methods by which pollution due to plastics can be solved.

Ans: Pollution due to plastics can be solved by following methods :

• Avoid the use of plastics as far as possible.
• Use bags, made of jute or cloth.
• Biodegradable and non-biodegradable wastes should be separated and disposed off separately.
• Plastics should be recycled and reused.