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Class 8th-Science: Chapter 5 – Coal and Petroleum

Natural Resources

Resources that are obtained from nature are known as natural resources.

For Example: Air, water, soil, minerals, sunlight, forests, moon etc.

In the light of the availability of various resources in nature, natural resources can be broadly classified into two kinds.

Types of Natural Resources

1.  Inexhaustible Natural Resources

These resources are present in unlinited quantity in nature and are not likely to be exhausted by human activities.

For Example: Sunlight, air, water, soil,

2.  Exhaustible Natural Resources

The amount of these resources in nature is limited. they can be exhausted by human activities.

For Example: forests, wildlife, minerals, coal, petroleum, natural gas etc.

Q.  Can we use all our natural resources forever?

Ans.  No, some natural resources (called exhaustible natural resources) are going to exhaust one day. So we cannot use them forever. For example: forests, wildlife, minerals, coal, petroleum, natural gas etc.

Q.  Can air, water and soil be exhausted by human activities?

Ans. No, these will not be exhausted by human activities.They are inexhaustible natural resources.

Q.  Is water a limitless resource?

Ans. Yes, water is a limitless resource because water cannot be finished or vanished from earth, it can be polluted by human activities but its end is not possible.

Coal

  1. Coal is as hard as stone and is black in colour.
  2. It is one of the fuels used to cook food.
  3. Earlier, it was used in railway engines to produce steam to run the engine.
  4. It is also used in thermal power plants to produce electricity.
  5. Coal is also used as a fuel in various industries.

Where do we get coal from and how is it formed?

About 300 million years ago the earth had dense forests in low lying wetland areas. Due to natural processes, like flooding, these forests got buried under soil. As more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal.

Q.  What is carbonisation?

Ans.  As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation.

A coal mine

When heated in air, coal burns and produces mainly carbon dioxide gas.

Carbon(coal) + Oxygen —> Carbon dioxide(gas) 

Coal is processed in industry to get some useful products such as coke, coal tar and coal gas.

A. Coke

  1. It is a tough, porous and black substance.
  2. It is almost pure form of carbon.
  3. Coke is used in the manufacture of steel and in the extraction of many metals.

B. Coal tar

  1. It is a black, thick liquid with unpleasant smell.
  2. It is a mixture of about 200 substances.
  3. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc.
  4. Interestingly, naphthalene balls used to repel moths and other insects are also obtained from coal tar.

These days, bitumen, a petroleum product, is used in place of coal-tar for metalling the roads.

C. Coal gas

Coal ia processed in industry to get some useful products such as coke, coal tar and coal gas.

  1. Coal gas is obtained during the processing of coal to get coke. 
  2. It is used as a fuel in many industries situated near the coal processing plants.

Coal gas was used for street lighting for the first time in London in 1810 and in New York around 1820. Now a days, it ia used as a source of heat rather than light.

Petroleum

1.  Petrol is used as a fule in light automobiles such as motor cycles/ scooters and cars.

2.  Heavy motor vehicles like trucks and tractors run on diesel.

3.  Petrol and diesel are obtained from a natural resource called petroleum.

Q.  Do you know how petroleum is formed?

Ans.  Petroleum was formed from organisms living in the sea. As 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 the dead organisms into petroleum and natural gas.

The world’s first oil well was drilled in pennsylvania, USA, in 1859. Eight years later, in 1867, oil was stuck at Makum in Assam. In India, oil is found in Assam, Gujarat, Mumbai High and in the river basins of Godavari and Krishna.

Refining of Petroleum

1.  Petroleum is a dark oily liquid.

2.  It has an unpleasant odour.

3.  It is a mixture of various contituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.

Q.  What is refining?

Ans.  The process of separating the various constituents/ fractions of petroleum is known as refining. It is carried  out in a petroleum refinery.

Table 5.1 Various constituenta of petroleum and their uses

S.No Constituents of petroleum Uses

  1. Petroleum Gas in Liquid form (LPG) Fuel for home and industry
  2. Petrol Motor fuel, aviation fuel, solvent for dry cleaning
  3. Kerosene Fuel for stoves, lamps and for jet aircrafts
  4. Diesel Fuel for heavy motor vehicles, electric generators
  5. Lubricating oil Lubrication
  6. Paraffin wax Ointments, candles, vaseline etc.
  7. Bitumen Paints, road surfacing
    Petrochemicals

Many useful substances are obtained from petroleum and natural gas. THese are termed as ‘Petrochemicals’.

These are used in the manufacture of detergents. fibres (polyester. nylon, acrylic ect.), polthene and other man-made plastics. Hydrogen gas obtained from natural gas, is used in the production of fertilisers (urea).

Due to its great commercial importance, petroleum is also called ‘black gold’. 

Fossils Fuel

Fossils:  The dead remains of living organisms are called fossils.

Fossil Fuels:  Fuels which are formed from the dead remains of organisms (called fossils) are called fossil fuels.

For Example:  Coal, petroleum and natural gas are fossil fuels.

Natural Gas

1.  Natural gas is a very important fossil fuel because it is easy to transport through pipes.

2.  Natural gas is stored under high pressure as compressed natural gas (CNG).

3.  CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel.

4.  The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes.

5.  Such a network of pipelines exists in vadodara (Gujarat), some parts of Delhi and other places.

6.  Natural gas is also used as a starting material for the manufacture of a number of chemicals and fertilisers.

7.  India has vast reserves of natural gas. In our country, natural gas has been found in Tripura, Rajasthan, Maharashtra and in the Krishna Godavari delta.

Q.  Can coal, petroleum and natural gas be prepared in the laboratory from dead organisms?

Ans.  No, Their formation is a very slow process and conditions for their formation cannot be created in the laboratory.

Tips to Save Petrol and Diesel

In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/diesel while driving. Their tips are:

Drive at a constant and moderate speed as far as possible,

Switch off the engine at traffic lights or at a place where you have to wait,

Ensure correct tyre pressure, and Ensure regular maintenance of the vehicle.

Chapter 5 Ncert Question Answer

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