NCERT Solutions for Class 8 Science Chapter 5 Coal And Petroleum

Q.1 What are the advantages of using CNG and LPG as fuels?

Answer :

ADVANTAGES OF USING CNG GAS

1) It is commonly referred as green fuel because it is free from lead and sulphur, thus leading to the reduction of harmful emissions.

2) CNG is less likely to auto-ignite on hot surfaces, since it has a high auto-ignition temperature i.e., 540 degree Celsius.

3) The operational cost of vehicles running on CNG is comparatively low than other fuels.

4) CNG vehicle can run using both CNG or Petrol.

5) CNG is certified as a safe fuel. As it is lighter than air, so in case of leakage, it rises up and disperses into the atmosphere easily and evenly.

ADVANTAGES OF USING LPG GAS

1) It exhibits clean burning.

2) It has high energy value and thus provides good flame control.

3) LPG is easy to store and doesn't have a problem of spillage.

4) Its maintenance cost is comparatively low.

5) It is environment friendly fuel with minimum sulphur contents & sulphur free emissions.

Q.2 Name the petroleum product used for surfacing of roads.

Answer :

Bitumen is the petroleum product used for surfacing of roads.

EXPLANATION :

It is a black viscous mixture of hydrocarbons obtained naturally or as a residue from petroleum distillation.

Bituminous materials are used for roofing and waterproofing.

It is strongly adhesive(sticky) and resistant to damage from water and oil spills

Q.3 Describe how coal is formed from dead vegetation. What is this process called?

Answer :

Coal was formed around 300 million years ago when the earth was covered with swampy forests. When plants in these forests, mainly trees, mosses, ferns, and reeds died, they fell into the swamps. Thus, there was a thick layer of dead vegetation in the swamp formed.

With passage of time, more and more plants died and got accumulated. Many such layers were formed, one above the another, thus pushing each layer more inside the earth surface where the topmost layers compressed the old layers.

Heat and pressure caused some physical and chemical changes and eventually, some carbon-rich deposits were formed.

This slow process of conversion of dead vegetation into coal is called carbonization.

Q.4 Fill in the blanks.
(a) Fossil fuels are ____________, ____________, and ____________ .
(b) Process of separation of different constituents from petroleum is called _____________ .
(c) Least polluting fuel for a vehicle is ______________ .

Answer :

(a) Fossil fuels are coal , petroleum and natural gas.

(b) Process of separation of different constituents from petroleum is called refining.

(c) Least polluting fuel for a vehicle is compressed natural gas.

EXPLANATION :

(a) Fossil fuels are hydrocarbons that includes coal, petroleum and natural gas. A fossil fuel is formed by anaerobic decomposition of buried dead organisms containing organic molecules.

(b) Petroleum refining processes are the chemical engineering processes used in petroleum refineries to transform crude oil into useful products such as liquefied petroleum gas, gasoline or petrol, kerosene, jet fuel, diesel oil and fuel oils.

(c) Compressed natural gas or CNG is a type of natural gas which is mainly composed of methane that is stored under high pressure in its gaseous form to transport it or for storage.

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

Answer :

a) Fossil fuels can be made in the laboratory. ( F )

b) CNG is more polluting fuel than petrol. ( F )

c) Coke is the almost pure form of carbon. ( T )

d) Coal tar is a mixture of various substances. ( T )

e) Kerosene is not a fossil fuel. ( F )

EXPLANATION :

1) Fossil fuels are formed from the remains of dead plants and animals under intense pressure and temperature for millions of years under the earth surface and as these conditions cannot be created in a laboratory, hence fossil fuels cannot be made in the laboratory.

2) CNG is more better than petrol and diesel as CNG is a natural gas which emits less nitrogen oxides (NOx) and particulate matter (PM) during combustion. It is also regarded as green fuel.

3) Coke is a grey, hard and porous fuel with a high carbon content and few impurities which is made by heating coal or oil in the absence of air.

4) The major classes of compounds present in coal-tar include: aromatic hydrocarbons, tar acids, tar bases, aromatic amines, sulphur-containing heterocyclic compounds, and oxygen-containing heterocyclic compounds. Hence this proves that coal tar is a mixture of various substances

5) Kerosene is extracted by refining petroleum. As petroleum is considered as a fossil fuel, hence kerosene is also a fossil fuel.

Q.6 Explain why fossil fuels are exhaustible natural resources.

Answer :

Fossil fuels take millions of years to be formed which includes the formation of coal, petroleum and natural gas.

When dead vegetation and animals get buried deep inside the earth under high temperature and pressure for millions of years, resulting in the compression of organic materials thus it leads to the formation of fossil fuels.

As these required conditions cannot be provided in a laboratory hence fossil fuels cannot be created in the laboratory.

As fossil fuels are present in limited quantity hence they are regarded as non-renewable resources. And reckless use of fossil fuels will gradually lead to their depletion.

Q.7 Describe the characteristics and uses of coke.

Answer :

CHARACTERISTICS OF COKE

1) Coke is a grey, hard and porous fuel.

2) Coke has a high carbon content.

3) Coke is prepared by heating coal or oil in the absence of air.

USES OF COKE

1) It is used mainly in iron ore smelting.

2) It is used as a fuel for stoves, furnaces and blacksmithing.

3) It is used to manufacture steel.

Q.8 Explain the process of the formation of petroleum.

Answer :

Petroleum is a fossil fuel which is also called as crude oil.

It was formed by the decomposition of organic matter over millions of years.

Petroleum is formed when large quantities of dead organisms primarily zooplankton and algae–underneath sedimentary rock, plants and animals that lived in shallow seas were mixed with other sediments and then, were subjected to intense heat and pressure.

The remains of these organisms that were compressed under high pressure & temperature, their fat content and water were transformed into fossil fuels.

Coal, natural gas, and petroleum are all fossil fuels that were formed under similar conditions.

Q.9 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.

Answer :