NCERT Solutions for Class 8 Science Chapter 5 : Coal and Petroleum

Q:

Name the petroleum product used for surfacing of roads.

A:

Bitumen is used for surfacing of roads.

Q:

Describe how coal is formed from dead vegetation. What is the process called?

A:

  1. About 300 million years ago the earth had dense forest in low lying wetlands. Due to natural processes like flooding and earthquakes, forests got buried under the soil. With the passage of time, as more and more soil got deposited on them, the buried plants were compressed. Deep down the earth, pressure and temperature was very high. Under high pressure and temperature, slowly plants got converted into coal.
  2. The slow process of conversion of dead vegetation into coal is called carbonisation.

Q:

Explain why fossil fuels are exhaustible natural resources.

A:

The amount of fossil fuels available in nature is limited. The formation of fossil fuels takes millions of years. Fossil fuels are made by the action of heat and pressure on the remains of dead vegetation and animals. The rate at which we are using them is very fast as compared to their rate of formation. Therefore, fossil fuels are exhaustible natural resources.

Q:

Fill in the blanks.
  1. Fossil fuels are __________, __________ and ___________.
  2. Process of separation of different constituents from petroleum is called _____________.
  3. Least polluting fuel for vehicle is _________.

A:

  1. coal, petroleum, natural gas
  2. refining
  3. CNG

Q:

The following table shows the total power shortage in India from 1991-1997. Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis.
S.No. Year Shortage (%)
1 1991 7.9
2 1992 7.8
3 1993 8.3
4 1994 7.4
5 1995 7.1
6 1996 9.2
7 1997 11.5

A:

Q:

Explain the process of formation of petroleum.

A:

  • Petroleum originated from the remains of sea organisms.
  • When sea organisms died, they got buried at the bottom of sea.
  • With passage of time, their bodies got covered with mud.
  • Pressure and temperature rose as they got buried lower and lower.
  • Due to the effect of heat, pressure and action of bacteria in the absence of air, the buried remains decomposed very slowly forming petroleum.

Q:

Describe characteristics and uses of coke.

A:

Coke is a black porous substance. It is obtained as residue during destructive distillation of coal. The characteristics of coke are as follows:

  1. Coke is an almost pure form of carbon.
  2. It burns almost with no smoke.
  3. It is a non-conductor of heat and electricity.

Uses of coke are as follows:

  1. Coke is used in the extraction of metals.
  2. It is also used in the manufacturing of steel.

Q:

Tick True/False against the following statements.
  1. Fossil fuels can be made in the laboratory. (T/F)
  2. CNG is more polluting fuel than petrol. (T/F)
  3. Coke is almost pure form of carbon. (T/F)
  4. Coal tar is a mixture of various substances.(T/F)
  5. Kerosene is not a fossil fuel. (T/F)

A:

  1. Fossil fuels can be made in the laboratory.   (F)
  2. CNG is more polluting fuel than petrol.         (F)
  3. Coke is almost pure form of carbon.             (T)
  4. Coal tar is a mixture of various substances.  (T)
  5. Kerosene is not a fossil fuel.                        (F)

Q:

What are advantages of using CNG and LPG as fuels?

A:

The advantages of using LPG as a fuel are as follows:

  1. LPG burns easily with smokeless flame. It is a clean fuel.
  2. LPG has high calorific value.
  3. LPG does not produce any poisonous gases on burning.
  4. LPG does not leave behind any solid residue on burning.

The advantages of using CNG as a fuel are as follows:

  1. CNG burns easily with smokeless flame. It is a clean fuel.
  2. CNG can be used directly for burning in homes and factories.
  3. CNG is used as a fuel for vehicles because it is less polluting.
  4. CNG is used as a fuel in thermal power stations for generating electricity.
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