Coal and Petroleum - Exemplar Solutions 4

CBSE Class 8 Science
NCERT Exemplar Solution
CHAPTER 5
Coal and Petroleum

LONG ANSWER QUESTIONS
27. Name the products obtained and their uses when coal is processed in industry.
Ans. Coal is processed in industry to get some useful products coke, coal tar and coal gas.
Coke is used in the manufacture of steel and in extraction of many metals.
Coal tar is used as starting material for manufacturing various sustances such as synthetic dyes, drugs, explosives, perfumes, paints etc.
Coal gas is used as fuel.

28. We say fossil fuels will last only for a few hundred years. Comment.
Ans. It takes a very long time and so much of pressure for the formation of fossil fuels. It also requires specific conditions and it doesn’t happen quite often. Therefore, their limited stock will last only for a few hundred years.

29. We read in newspapers that burning of fuels is a major cause of global warming. Explain why.
Ans.A large amount of COproduced during combustion of fuels, CO2 is a green house gass whose amount on earth would always be maintained .Global warming occurs when carbon dioxide (CO2) and other air pollutants and other greenhouse gasses collect in the atmosphere and absorb sunlight and solar radiation that have bounced off the earth’s surface. Normally, this radiation would escape into space—but these gasses, trap the heat and cause the planet to get hotter. That's what's known as the greenhouse effect. This finally leads to heating up of earth’s atmosphere and is main cause of global warming.

30. While driving, what are the tips we must follow to save petrol/ diesel/natural gas?
Ans
• Ensure correct tire pressure.
• Ensure regular maintenance of the vehicle.
• Drive at a constant and moderate speed.
• Switch off the engine at traffic lights or at a place where you have to wait.

31. Imagine that all the exhaustible natural resources are exhausted by human activities. Do you think survival of living beings would be possible.? If yes, why? If not, why not?
Ans. In the absence of all the exhaustible natural resources our life would be tremendously affected. These exhaustible natural resources are used for manufacturing various articles that we use in our day-to-day life. Some of the basic uses of the fossil fuels are as follows:
Uses of natural gas:
  • Natural gas stored under high pressure in the form of compressed natural gas(CNG) is used for power generation.
  • It is used as fuel for automobiles.
  • It can be directly used for burning and hence finds extensive use at homes in cooking cylinders and industries for generating energy.
  • It is used as a preliminary material in many manufacturing industries like manufacturing chemicals and fertilisers.

32. Why petrol is exhaustible natural resource, whereas sunlight is not? Explain.
Ans. Sunlight is a light we are getting froms sun and it is present in unlimited amount on earth weareas petrol is getting from a long process and immense pressure to form fossil fuel so it is an exhaustible resourse.

33. Write some important uses of the various constituents of petroleum.
Ans.
  • Petroleum gas in liquid form (LPG) — used as fuel for home and industry.
  • Petrol — used as fuel for automobile and aviation.
  • Kerosene — used as fuel for stoves, lamps and for jet aircrafts.
  • Diesel — used as fuel for heavy motor vehicles, electric generators.
  • Lubricating oil — used for lubrication
  • Praffin wax — used in ointments, candles, vaseline etc.
  • Bitumen — used in paints and road surfacing.

34. Coal reserves are said to be enough to last for another hundred years. Do you think we need to worry in such case? Why or why not?
Ans. Yes, we do need to worry towards this threat looming large because coal is needed in our day-to-day life and its not possible to make it again on earth .

35. What steps would you suggest for the judicious use of fossil fuels?
Ans. Judicious use of fossil fuels can be done by following the steps as mentioned below:
  • Use public transport
  • Encouraging Car-pooling for going to school and work.
  • Minimise the use of fossil fuels by switching over to renewable energy sources like solar energy, hydel energy, geothermal energy to produce heat and electricity.
  • Use biogas as domestic fuel instead of LPG.
  • Using vehicles driven by solar energy.

36. Complete the crossword Fig. 5.2 with the help of the clues:
Across
1. Fuels obtained from dead remains of living organisms. (6,5)
2. A process by which the various constituents of petroleum are separated. (8)
3. A porous black substance obtained from coal. (4)
4. Another name for motor fuel. (6)
Down
5. The substance obtained by carbonisation. (4)
6. Fuel for heavy motor vehicles. (6)
7. A petroleum product used for road surfacing. (7)
8. Dead remains of sea animals got converted into it. (9)
Ans.