Maharashtra State Board

📘 Standard VIII – Science

Chapter 17: Man-Made Materials

🔎 1. Try to Find It

a. Plastic shows ______ property; hence it can be moulded into any shape.
Ans: Plasticity

b. Motor cars are coated with ______.
Ans: Teflon

c. Thermocol melts at ______ °C.
Ans: More than 100 °C

d. ______ glass dissolves in water.
Ans: Alkali silicate

🤝 2. Who Is My Partner?

‘A’ Column‘B’ Column
a. Lead glassiii. Electric bulb
b. Bakeliteiv. Electric switch
c. Thermocoli. Plates
d. Optic glassv. Lens
e. Polypropyleneii. Mattresses

✏️ 3. Answer the Following

a. Thermocol is produced from which material?

Ans: Thermocol is produced from a thermoplastic material called polystyrene.

b. Write the uses of PVC.

Ans: PVC (Polyvinyl Chloride) is used for manufacturing:

  • Bottles
  • Raincoats
  • Pipes
  • Shoes
  • Furniture
  • Ropes
  • Toys
  • Handbags
  • Electric cable insulation

c. Write the natural or man-made raw material of the following items.

ItemNatural / Man-made Raw Material
MattressMan-made (foam, coir, cotton)
Glass vesselMan-made (glass)
BangleMan-made (glass/plastic)
ChairNatural (wood) / Man-made (plastic)
Gunny bagNatural (jute)
BroomNatural (grass/coconut leaves)
KnifeMan-made (steel)
PenMan-made (plastic)

d. Which are the main ingredients of glass?

Ans: The main ingredients of glass are:

  • Sand (silica)
  • Soda
  • Limestone
  • Small quantity of magnesium oxide

e. How is plastic produced?

Ans:

  1. Plastics are produced from natural organic materials like crude oil, natural gas, coal, and cellulose.
  2. The process begins with the distillation of crude oil in a refinery.
  3. Naphtha, one of the fractions obtained, is used for plastic production.
  4. Plastics are formed through polymerization (addition or condensation).
  5. Small molecules called monomers join together to form long chains called polymers.
  6. The material is melted, cooled, and converted into small pellets.
  7. These pellets are shaped into products using methods such as:
    • Extrusion: Used to make plastic films
    • Injection moulding: Used to make containers
    • Blow moulding: Used to make bottles
    • Rotational moulding: Used to make large hollow items like tanks and toys

🔄 4. Distinguish Between

a. Man-Made Materials and Natural Materials

Man-Made MaterialsNatural Materials
Made by humans after research and processing.Obtained directly from nature.
Usually non-biodegradable.Mostly biodegradable.
Examples: Plastic, glass, thermocolExamples: Jute, wood, cotton, paper

b. Thermoplastic and Thermosetting Plastic

ThermoplasticThermosetting Plastic
Can be moulded and remoulded on heating.Cannot be remoulded after heating.
Can be recycled.Cannot be recycled easily.
Used for bottles, pipes, handbags, etc.Used for cooker handles, electric switches, insulation.
Examples: PVC, polystyrene, polyethylene, polypropyleneExamples: Bakelite, melamine, polyester

🌍 5. Answer in Your Own Words

a. Explain the effects and remedial measures of the following materials on environment and human health.

1. Plastic

Effects:

  1. Plastic is non-biodegradable and causes pollution.
  2. It blocks drainage systems.
  3. Animals may swallow plastic and die.
  4. Burning plastic releases harmful gases.
  5. It pollutes water bodies and harms marine life.
  6. It remains in landfills for thousands of years.

2. Glass

Effects:

  1. Glass is non-biodegradable.
  2. Its production emits harmful greenhouse gases.
  3. Broken glass can harm humans and animals.
  4. Waste glass can block drainage systems.

3. Thermocol

Effects:

  1. Thermocol is non-biodegradable.
  2. Long-term exposure may cause serious health issues.
  3. Burning thermocol releases poisonous gases.
  4. Reheating food in thermocol containers may be harmful.

b. Which measures will you take to minimize environmental problems caused by non-degradable plastic?

Ans: Follow the 4R Principle:

  1. Reduce – Use less plastic.
  2. Reuse – Use plastic items repeatedly.
  3. Recycle – Reprocess plastic materials.
  4. Recover – Convert waste into energy.

Alternatives:

  • Use cloth or jute bags instead of plastic bags.
  • Use biodegradable food wraps.
  • Replace plastic cutlery with eco-friendly materials.
  • Prefer paper or cloth products.

📝 6. Write Short Notes

a. Glass Production

  1. Glass is a hard, non-crystalline material made mainly from silica.
  2. Sand, soda, limestone, and magnesium oxide are heated in a furnace.
  3. The mixture melts at very high temperatures (about 1500 °C).
  4. The molten mixture is cooled rapidly to form transparent glass.

b. Optic Glass

  1. Optical glass is high-quality pure glass.
  2. It is made from sand, soda, limestone, barium oxide, and boron.

Uses:

  • Spectacle lenses
  • Camera lenses
  • Microscopes
  • Telescopes
  • Prisms

c. Uses of Plastic

  1. Used in healthcare (e.g., syringes).
  2. Used for microwave-safe containers.
  3. Teflon coating protects vehicles from scratches.
  4. Used in aeroplane parts.
  5. Polyacrylic plastic is used to make lenses and artificial teeth.
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