1. Explain why some fibres are called synthetic.
Ans:
Fibres are called synthetic because they are man-made and are prepared using chemicals in laboratories or industries. These fibres are not obtained naturally but are created by joining small chemical units called monomers to form long chains known as polymers.
Examples of synthetic fibres include nylon, rayon, acrylic, and polyester.
2. Mark the correct answer.
Rayon is different from synthetic fibres because
(a) it has a silk-like appearance.
(b) it is obtained from wood pulp.
(c) its fibres can also be woven like those of natural fibres.
Ans:
The answer is (b) it is obtained from wood pulp.
3. Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called __________ or __________ fibres.
(b) Synthetic fibres are synthesised from the raw material called __________.
(c) Like synthetic fibres, plastic is also a __________
Ans:
(a) artificial or man-made
(b) petrochemicals.
(c) polymer
4. Give examples which indicate that nylon fibres are very strong.
Ans:
The following examples indicate the strength of nylon fibres:
Parachutes and rock climbing ropes are made of nylon due to its high tensile strength.
Nylon is used in making seat belts, fishing nets, and tyre cords because it can withstand a lot of stress.
Nylon is used in manufacturing sports accessories, such as rackets, because of its durability and strength.
5. Explain why plastic containers are favoured for storing food.
Ans:
Plastic containers are favoured for storing food due to the following reasons:
Non-reactive: Plastics do not react with the ingredients of food, ensuring the food remains safe and uncontaminated.
Lightweight and durable: Plastic containers are easy to handle and less prone to breaking compared to glass or ceramic containers.
Waterproof and airtight: Plastic containers help in keeping the food fresh by preventing moisture and air from entering.
Cost-effective: Plastics are affordable and widely available for storage purposes.
6. Explain the difference between thermoplastic and thermosetting plastics.
Ans:
The difference between thermosetting plastics and thermoplastics are as follows:
7. Explain why the following are made of thermosetting plastics.
Ans:
a) Saucepan handles
Thermosetting plastics are used to make saucepan handles because:
They are bad conductors of heat, ensuring that heat from the pan does not transfer to the handle.
They do not soften or melt when exposed to high temperatures.
b) Electric plugs, switches, and plug boards
Bakelite, a type of thermosetting plastic, is used because:
It is a bad conductor of electricity, preventing electric shocks.
It can withstand high temperatures and does not deform or melt, ensuring safety and durability.
8. Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.
Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
9.Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Ans:
Rana should buy cotton shirts for the summer instead of synthetic shirts. Cotton is a natural fiber that absorbs sweat effectively and allows it to evaporate, keeping the body cool. Synthetic materials, on the other hand, do not absorb sweat and may cause discomfort in the heat.
10.Give examples to show that plastics are non-corrosive in nature.
Ans:
Plastics are non-corrosive because they do not react with water, air, or chemicals. For instance:
Cleaning agents, like acids and bases, are stored in plastic containers.
Water pipes made of plastic are used as they do not corrode like metal pipes.
11. Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.
Ans:
No, the handle and bristles of a toothbrush should not be made of the same material. The handle needs to be hard, durable, and strong for easy grip, while the bristles should be soft and flexible to clean teeth gently without harming gums.
12. ‘Avoid plastics as far as possible’. Comment on this advice.
Ans:
This advice is valid as plastics are non-biodegradable and cause severe environmental pollution. Plastics take hundreds of years to decompose and, when burned, release toxic gases that pollute the air. Plastics disposed of in landfills or water bodies harm animals and aquatic life, as they may swallow them, leading to fatal consequences. Opting for eco-friendly materials like paper or cloth can significantly reduce plastic pollution.
13. Match the terms of column A correctly with the phrases given in column B
14. ‘Manufacturing of synthetic fibres is actually helping conservation of forests’. Comment.
Ans:
The manufacturing of synthetic fibres helps conserve forests because natural fibres such as silk, cotton, and jute are derived from plants, which often leads to deforestation or the destruction of natural habitats to obtain raw materials. By producing synthetic fibres, the dependency on plants for natural fibres is reduced, thus helping to conserve forests and preserve the environment.
15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Ans:
To demonstrate that thermoplastic is a poor conductor of electricity, follow the steps below:
Materials Required:
A bulb
Connecting wires
A battery
A piece of metal
A plastic pipe (thermoplastic)
Procedure:
Create an electric circuit with a bulb, battery, and connecting wires.
Insert a piece of metal into the circuit as a conductor. Switch on the current. Observe that the bulb glows because the metal allows electricity to flow.
Replace the metal piece with a plastic pipe (thermoplastic) in the circuit. Switch on the current again.
Observation:
The bulb does not glow when the plastic pipe is part of the circuit.
Conclusion:
This activity demonstrates that thermoplastic is a poor conductor of electricity because it does not allow electric current to pass through it.