Class 8 Science Notes Chapter 5 (Chapter 5) – Examplar Problems Book

Alright class, let's focus on Chapter 5: Coal and Petroleum from your Science Exemplar book. This is a crucial chapter, not just for your class exams but also for various government competitive exams where General Science is a component. Pay close attention to the definitions, processes, and uses.

Chapter 5: Coal and Petroleum - Detailed Notes for Exam Preparation

1. Natural Resources:

• Materials obtained from nature that are useful to humans.
• Classification based on availability:
  • Inexhaustible Natural Resources: Present in unlimited quantity in nature and are not likely to be exhausted by human activities.
    • Examples: Sunlight, Air, Water (though usable fresh water is limited).
  • Exhaustible Natural Resources: Present in limited quantity in nature and can be exhausted by human activities over time.
    • Examples: Forests, Wildlife, Minerals, Coal, Petroleum, Natural Gas.

2. Fossil Fuels:

• These are exhaustible natural resources formed from the dead remains of living organisms (fossils) buried under the Earth millions of years ago.
• High temperature and pressure deep inside the Earth converted these dead remains into fossil fuels.
• Main Examples: Coal, Petroleum, Natural Gas.

3. Coal:

• Formation: Formed from dead vegetation (trees, ferns, plants) buried under swamps millions of years ago. Due to geological processes, layers of soil deposited over them. Under high pressure and high temperature, and in the absence of air, this buried vegetation slowly got converted into coal.
• Carbonisation: The slow process of conversion of dead vegetation into coal is called carbonisation. Since coal is mainly carbon, this process is aptly named.
• Properties: Hard, stone-like, black in colour.
• Uses:
  • Used as fuel for cooking and heating.
  • Used in thermal power plants to produce electricity.
  • Used as fuel in various industries.
  • Used earlier in steam engines.
  • Used to manufacture coke, coal tar, and coal gas.
• Processing of Coal (Destructive Distillation): When coal is heated strongly in the absence of air, it yields useful products. This process is called destructive distillation.
  • Coke:
    • Tough, porous, and black substance.
    • Almost pure form of carbon (about 98%).
    • Uses: Manufacture of steel, extraction of many metals (as a reducing agent), fuel.
  • Coal Tar:
    • Thick, black liquid with an unpleasant smell.
    • A mixture of about 200 different carbon compounds.
    • Uses: Source of raw materials for manufacturing synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, naphthalene balls (to repel moths). Note: Bitumen, a petroleum product, is now often used instead of coal tar for metalling roads.
  • Coal Gas:
    • Obtained during the processing of coal to get coke.
    • Mixture of gases (mainly hydrogen, methane, carbon monoxide).
    • Uses: Used as a fuel in industries situated near coal processing plants. Historically used for street lighting.

4. Petroleum:

• Formation: Formed from organisms living in the sea (mainly plankton). When these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, absence of air, high temperature, and high pressure transformed these dead organisms into petroleum and natural gas.
• Occurrence: Found trapped between layers of impervious rocks, often along with natural gas above the petroleum layer. Water is usually found below the oil layer (as oil and gas are lighter than water).
• Extraction: Extracted by drilling oil wells through the Earth's crust and rock layers.
• Properties: Dark, oily, viscous liquid with an unpleasant odour. It is a complex mixture of various hydrocarbons. Also known as 'Crude Oil' or 'Black Gold' due to its great commercial importance.
• Refining of Petroleum: The process of separating the various constituents/fractions of petroleum is known as refining. It is carried out in a petroleum refinery using the technique of Fractional Distillation. This process works because different components of petroleum have different boiling points.
  • Fractions Obtained and their Uses:
    • Petroleum Gas (LPG - Liquefied Petroleum Gas): Fuel for home and industry.
    • Petrol (Gasoline): Motor fuel, aviation fuel, solvent for dry cleaning.
    • Kerosene: Fuel for stoves, lamps, and jet aircraft.
    • Diesel: Fuel for heavy motor vehicles, electric generators.
    • Lubricating Oil: Lubrication of machines.
    • Paraffin Wax: Ointments, candles, vaseline, wax paper.
    • Bitumen: Paints, road surfacing (metalling).
• Petrochemicals: Many useful substances obtained from petroleum and natural gas are termed 'Petrochemicals'.
  • Uses: Manufacture of detergents, synthetic fibres (polyester, nylon, acrylic), polythene and other man-made plastics, fertilisers (urea), synthetic rubber.

5. Natural Gas:

• Occurrence: Found trapped above petroleum deposits in oil wells. Also found in places without petroleum.
• Composition: Mainly methane (CH₄), with smaller amounts of ethane, propane.
• Importance: Important fossil fuel because it is easy to transport through pipes.
• CNG (Compressed Natural Gas): Natural gas stored under high pressure.
  • Advantages: Used as fuel for transport vehicles (less polluting), used for power generation. Burns cleanly, leaving no ash. Can be supplied directly to homes and factories through pipelines.
  • Uses: Starting material for the manufacture of a number of chemicals and fertilisers.

6. Limitations and Conservation of Fossil Fuels:

• Exhaustible: Fossil fuels are limited and took millions of years to form. Current consumption rates are high, leading to depletion.
• Pollution: Burning fossil fuels releases harmful substances:
  • Carbon dioxide (CO₂): A major greenhouse gas contributing to global warming.
  • Sulphur dioxide (SO₂) and Nitrogen oxides (NOx): Cause acid rain, harmful to crops, buildings, soil, and aquatic life.
  • Carbon monoxide (CO): Poisonous gas produced during incomplete combustion.
  • Soot (unburnt carbon particles): Cause respiratory problems.
• Conservation: It is essential to use fossil fuels judiciously.
  • PCRA (Petroleum Conservation Research Association) advises:
    • Drive vehicles at a constant and moderate speed.
    • Switch off engines at traffic lights or short stops.
    • Ensure correct tyre pressure.
    • Ensure regular vehicle maintenance.
  • Use alternative energy sources (solar, wind, hydro).
  • Use public transport, carpooling, cycling, walking.
  • Switch off lights, fans, and appliances when not in use.

Multiple Choice Questions (MCQs)

1. Which of the following is an inexhaustible natural resource?
   (a) Coal
   (b) Petroleum
   (c) Sunlight
   (d) Forests

2. The slow process of conversion of dead vegetation into coal is called:
   (a) Carbonisation
   (b) Refining
   (c) Distillation
   (d) Combustion

3. Which product obtained from coal is almost a pure form of carbon?
   (a) Coal Gas
   (b) Coal Tar
   (c) Coke
   (d) Bitumen

4. The process used to separate different fractions from petroleum is known as:
   (a) Carbonisation
   (b) Destructive Distillation
   (c) Fractional Distillation
   (d) Filtration

5. Which petroleum product is commonly used for road surfacing?
   (a) Petrol
   (b) Kerosene
   (c) Lubricating oil
   (d) Bitumen

6. CNG primarily consists of which gas?
   (a) Hydrogen
   (b) Methane
   (c) Carbon Monoxide
   (d) Butane

7. Which of the following is NOT a fossil fuel?
   (a) Coal
   (b) Natural Gas
   (c) Wood
   (d) Petroleum

8. Burning of fossil fuels contributes significantly to which environmental problem?
   (a) Ozone layer depletion
   (b) Water pollution
   (c) Global warming
   (d) Soil erosion

9. Substances derived from petroleum and natural gas used to manufacture plastics and fibres are called:
   (a) Petrochemicals
   (b) Fertilisers
   (c) Hydrocarbons
   (d) Polymers

10. Which action helps in conserving fossil fuels?
    (a) Using private vehicles more often
    (b) Keeping vehicle engines on at traffic signals
    (c) Using public transport or carpooling
    (d) Driving at very high speeds

Answers to MCQs:

1. (c) Sunlight
2. (a) Carbonisation
3. (c) Coke
4. (c) Fractional Distillation
5. (d) Bitumen
6. (b) Methane
7. (c) Wood
8. (c) Global warming
9. (a) Petrochemicals
10. (c) Using public transport or carpooling

Study these notes thoroughly. Remember the definitions, the processes like carbonisation and fractional distillation, the products obtained from coal and petroleum, and their specific uses. Understanding the environmental impact and the need for conservation is also very important for competitive exams. Good luck with your preparation!