Class 8 Science - CBSE Guide NCERT Solutions
Coal and Petroleum
NCERT answers for CBSE Class 8 Science Chapter 5 Exercise Questions (NCERT Solutions)
Question.1: What are the advantages of using CNG and LPG as fuels?
Answer: Following are the advantages of using CNG (compressed natural gas) and LPG (liquefied petroleum gas):
(1) They can be burnt directly.
(2) They can be transported easily through pipe lines.
(3) They are cleaner fuels and produce very less pollution on usage.
(4) Produces more heat energy when burnt in comparison to other fuels.
Question.2: Name the petroleum product used for surfacing of roads?
Answer: Bitumen or coal tar is used for surfacing of roads.
Question.3: Describe how coal is formed from dead vegetation. What is this process called?
Answer: About 300 million years ago the earth had dense forests in the low lying wetland areas. Due to natural processes like - flood, storm, earthquake etc. these forests got buried under the soil. Due to increasing load of the overburden, they got compressed. When they got buried deep in the soil, they were exposed to very high pressure and temperature. Under these conditions these dead buried plants slowly and gradually converted into coal.
This gradual process of formation of coal from dead vegetation is called ‘Carbonisation’.
Question.4: Fill in the blanks:
(a) Fossil fuels are ______, ______ and _______.
(b) On destructive distillation of coal ________, _______ and _______ are obtained.
(c) Process of separation of different constituents from petroleum is called _________.
(d) Least polluting fuel for vehicle is ________.
Answer: (a) coal, petroleum and natural gas. (b) coke, coal-tar and coal gas. (c) refining. (d) CNG
Question.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 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) False (b) False (c) True (d) True (f) False
Question.6: Explain why fossil fuels are exhaustible natural resources.
Answer: Fossil fuels require millions of years for their formation by nature. They cannot be formed artificially. Since the amount of these resources in nature is limited and the rate of consumption of these fossil fuels is very high so, it will come to an end by human usage. Therefore, fossil fuels are considered as exhaustible natural resources.
Question.7: Describe characteristics and uses of coke.
Answer: Coke is obtained by burning coal in absence of air and so it is a secondary product. It is a tough, porous and black substance. It is an almost pure form of carbon. So when it burns it gives heat without any smoke.
Coke is used in the manufacturing of steel and in the extraction of many metals.
Question.8: Explain the process of formation of petroleum.
Answer: Petroleum is a fossil fuel. It is formed beneath the earth by sea organisms which died millions of years ago. As these organisms died, their bodies settled at the bottom of the sea and got covered with the layers of sand and clay. Over millions of years in absence of air and due to high temperature and pressure beneath the earth, these dead organisms transformed into ‘petroleum’ and ‘natural gas’.