17. Man Made Materials
Complete solutions to the Exercises. Maharashtra State Board (Balbharati), Grade Eight General Science.
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Exercises
(a) Plastic shows plasticity property, hence it can be moulded to any shape.
(b) Motor cars are coated with Teflon.
(c) Thermocol melts at 100 °C.
(d) Alkali silicate glass dissolves in water.
| ‘A’ column | ‘B’ column |
|---|---|
| a. Lead glass | iii. Electric bulb |
| b. Bakelite | iv. Electric switch |
| c. Thermocol | i. Plates |
| d. Optic glass | v. Lens |
| e. Polypropylene | ii. Mattresses |
(a) Thermocol is produced from which material?
Thermocol is produced from polystyrene.
(b) Write uses of PVC.
PVC is used to make bottles, raincoats, pipes, handbags, shoes, cable insulation, furniture and toys.
(c) Write the natural or manmade raw material of the following items.
- Mattress – Polypropylene (manmade)
- Beaker – Glass (manmade)
- Bangle – Glass (manmade)
- Chair – Wood (natural)
- Gunny bag – Jute (natural)
- Broom – Coconut fibres, grass (natural)
- Knife – Steel (manmade)
- Pen – Plastic (manmade)
(d) Which are the main ingredients of glass?
Sand (silica), soda and lime are the main ingredients of glass. A little magnesium oxide is also added.
(e) How is the plastic produced?
Plastic is made of polymers. A polymer is a long chain formed by joining many small units. These units are obtained from petroleum. They are joined by heat and pressure in factories. The plastic is then given the required shape in moulds.
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(a) Manmade material and natural material
| Natural material | Manmade material |
|---|---|
| It is obtained from nature. | It is made in factories. |
| It is mostly degradable. | It is mostly non-degradable. |
| It causes less pollution. | It causes more pollution. |
| Examples: Wood, cotton, jute. | Examples: Plastic, glass, thermocol. |
(b) Thermoplastic and thermosetting plastic
| Thermoplastic | Thermosetting plastic |
|---|---|
| It softens on heating. | It does not soften on heating. |
| It can be moulded again and again. | Its shape cannot be changed once it is set. |
| Examples: Polythene, PVC. | Examples: Bakelite, melamine. |
(a) Explain the effect of the following materials on environment and human health.
1. Plastic:
- Plastic is non-degradable. It makes the soil infertile.
- Plastic bags block drains.
- Animals eating plastic fall ill and may die.
- Burning plastic releases poisonous gases.
2. Glass:
- Making glass needs high heat. Burning fuel releases harmful gases.
- Glass is non-degradable.
- Broken glass causes injuries.
3. Thermocol:
- Thermocol is non-biodegradable.
- Styrene in thermocol may cause cancer.
- Burning thermocol releases poisonous gases.
(b) Which measures will you arrange to minimize the environmental problems arising due to non-degradable plastic?
I will follow the 4R principle:
- Reduce: Use less plastic. Carry a cloth bag to the market.
- Reuse: Use plastic bottles and jars again.
- Recycle: Give plastic waste for recycling.
- Recover: Recover useful material from plastic waste.
I will not burn plastic or throw it in water.
(a) Glass production
- Sand, soda, lime and magnesium oxide are mixed in a furnace.
- Pieces of waste glass are added. So the mixture melts at 850 °C.
- The molten mixture is heated up to 1500 °C.
- Then it is cooled suddenly. It becomes transparent glass.
- The glass is given the required shape.
Glass manufacturing process.
(b) Optic glass
Optic glass is made from sand, soda, limestone, barium oxide and boron. It is very pure and clear. It is used to make spectacle lenses and lenses of cameras, microscopes and telescopes.
(c) Uses of plastic
- PVC: Pipes, bottles, raincoats, shoes.
- Polystyrene: Parts of refrigerators, toys.
- Polyethylene: Milk bags, packing bags.
- Polypropylene: Ropes, mattresses.
- Bakelite: Electric switches.
- Melamine: Cups, plates.
- Polyurethane: Seats of vehicles.
- Polyester: Textile industry.