Solved examples for class 8 science : Chapter 5

    Coal and Petroleum

    I. Multiple Choice Questions (MCQs).
    Q.1. The variety of coal used as a household fuel and in industries is
    a) peat
    b) bituminous
    c) lignite
    d) anthracite

    Answer. (b) bituminous

    Q.2. A product of coal used in the extraction of iron from iron oxide in a blast furnace, is
    a) coke
    b) coal tar
    c) coal gas
    d) none of these

    Answer. (a) coke

    Q.3. Petroleum is known as
    a) crude oil
    b) black gold
    c) both (a) and (b)
    d) none of these

    Answer. (a) crude oil

    Q.4. The process of separating crude oil into different useful components by fractional distillation is called
    a) refining
    b) separating
    c) degrading
    d) none of these
    Answer. (a) refining
    Q.5. Which of the following is less polluting and a cleaner fuel?
    a) Petrol
    b) Diesel
    c) Coal
    d) CNG
    Answer. d) CNG

    II. Fill in the blanks by selecting appropriate words from the given list: List : infrared, coal, fossil, carbon, methane

    Q.1. Coal, petroleum and natural gases are known as _______ fuels.
    Q.2. The coal found at greater depths is rich in _______ and poor in moisture content.
    Q.3. Wood undergoes anaerobic thermal degradation to form _____ .
    Q.4. Natural gas is a gaseous fossil fuel consisting mainly of _____ .
    Q.5. The heating up of the atmosphere occurs due to the trapping of ____ radiations by the carbon dioxide gas.
    Answer.
    1- fossil ,
    2- carbon ,
    3- coal ,
    4- methane ,
    5- infrared

    III. Match the items of Column A with those of Column B.

    Answer: 1-c, 2-d, 3-b, 4-e, 5-a,

    IV. Write ‘T’ for the true and ‘F’ for the false statements.

    Q.1. The use of the natural resources make our life smooth and comfortable.
    Q.2. Fossils are remains of plants and animals trapped between layers of rock.
    Q.3. Petroleum is obtained by drilling holes into the earth’s crust.
    Q.4. Paraffin wax is used for surfacing roads, making paints and weather proofing materials.
    Q.5. Natural gas is found only in coal mines among the coal beds.
    Answer: 1-T, 2-T, 3-T, 4-F,5-T

    V. Very Short Answer Questions.

    Q.1. Name the resources, which are continually renewed by nature.
    Answer: Sunlight, air and water

    Q.2. Name the fuels which are formed from the remains of plants and animals.
    Answer: Coal, petroleum and natural gas

    Q.3. Name the process of conversion of wood into coal in the absence of air.

    Answer: Carbonisation.

    Q.4. Name the process of separating crude oil into different useful components by fractional distillation.
    Answer: Refining.

    Q.5. Name the gaseous fossil fuel consisting mainly of methane.
    Answer: Natural gas

    VI. Short Answer Questions.
    Q.1. Why is coke considered as a clean fuel?
    Answer: Since coke mainly consists of carbon, so it is considered as a clean fuel.

    Q.2. What do you understand by petrochemicals?
    Answer: The chemical compounds that originate from petroleum are known as petrochemicals.

    Q.3. What do you mean by global warming?
    Answer: The increase in the temperature of the earth due to increase in the concentration of CO2 in air is known as global warming.

    Q.4. What are natural resources? Describe its kinds with proper examples.
    Answer: There are numerous Living and non-living substances found in nature which we use every day. Some of them are land, air, water, sunlight, minerals, forests, animals, etc. They are known as natural resources.
    The natural resources can be broadly classified into two types on the basis of their availability in nature.

    (i) Inexhaustible Natural Resources: These resources are continually renewed by nature and are not Likely to get exhausted. We say that the resources are Limitless. Sunlight and air are examples of such natural resources.

    (ii) Exhaustible Natural Resources: These natural resources are present in a fixed or limited amount. They can be exhausted by human activities as natural processes cannot renew them fast enough. Minerals, forest, wildlife, coal, petroleum and natural gases are examples of some exhaustible natural resources.

    Q.5. What do you mean by coal? Mention the varieties of coal along with their carbon content.

    Answer: Coal is a hard, black or brown coloured fossil fuel. It contains mainly carbon because it is formed from plants which are composed of carbon compounds.


    Q.6. Discuss some useful products obtained from coal.

    Answer: When coal is heated strongly in the absence of air (destructive distillation) coke, coal tar and coal gas are obtained.

    Coke : It is a black, tough and porous solid residue obtained by the distillation of bituminous variety of coal. It consists of mainly carbon and is a clean fuel. It is used in the extraction of iron from iron oxide in a blast furnace and in the manufacture of steel by Bessemer process.

    Coal tar : Distillation of coal tar yields several fractions which include benzene, toluene, xylene, naphthalene, anthracene, etc., which are known as

    coal tar crudes. They form the starting material for the synthesis of dyes, drugs, perfumes, explosives, preservatives, flavourings, synthetic resins, paints, plastics, photographic material and various other products. The residual fraction, pitch, is used as roofing material, for waterproofing and insulation.
    Coal gas: It is a gaseous mixture of hydrogen, methane, carbon monoxide and other gases. It is a source of fuel for domestic cooking. Nowadays it is used as a fuel in the industries which are situated near coal processing plants.

    VII. Long Answer Questions.
    Q.1. What do you understand by petroleum? How was it formed?

    Answer: Petroleum is derived from the Latin word “petra” meaning rock and “oleum” meaning oil. It is found deep inside the earth between layers of porous and non-porous rocks. Petroleum is a dark, viscous, fluorescent and oily liquid with an unpleasant odour. It consists of a mixture of hydrocarbons and cannot be used for any purpose. So, it is known as crude oil. It is also known as black gold. The chemical compounds that originate from petroleum are known as petrochemicals.

    Petroleum was formed due to bacterial decomposition of the remains of marine organisms that collected on the sea bed millions of years ago. As the remains sank deeper under the Layer of sand and mud, they were subjected to high temperature and pressure. A part of the remains liquefied while the others changed to gas, the liquid part, known as petroleum.

    Q.2. Describe occurrence of petroleum. How is it refined? Discuss some of its fractions and their uses.
    Answer: The Largest petroleum reserves are found in the Middle East. It includes countries Like Saudi Arabia, Kuwait, Iran and Iraq. USA is the largest producer of petroleum in the world accounting for nearly 50 % of the total output. Russia, Siberia, China and Canada are other countries with large oil reserves. In India, petroleum is found in Assam, Gujarat, Mumbai High and deltas of Krishna and Godavari.

    Refining of Petroleum

    The process of separating crude oil into different useful components by fractional distillation is called refining. The components are known as fractions. The method involves vaporising the crude oil, in a tubular furnace at 400 °C, and passing the vapours into a Long fractionating column. The highest boiling fraction condense near the lower part of the column while the low boiling fractions condense at different heights in the fractionating columns. The uncondensed gas, known as petroleum gas escapes through an outlet situated at the top of the column.


    Q.3. (a) What do you mean by natural gas?
    (b) Discuss pollution caused by combustion of fuels briefly.
    Ans. a) Natural gas is a gaseous fossil fuel consisting mainly of methane. It is found in oil fields along with crude oil or in natural gas fields. It is also found in coal mines among the coal beds.

    b) The combustion of most of the fuels produce gases such as carbon monoxide, carbon dioxide, oxides of nitrogen and oxides of sulphur. Solid fuels produce smoke which consists of unburnt carbon particles and also leave behind ash. These gases, along with carbon particles in smoke, cause air pollution. The ash may cause air, water or soil pollution, if not properly disposed.

    An increase in the concentration of carbon dioxide in the atmosphere leads to an increase in the temperature of the earth. The heating up of the atmosphere, occurs due to the trapping of infrared radiations, by the gas. This phenomenon is known as greenhouse effect. It leads to global warming.
    The oxides of sulphur, oxides of nitrogen and carbon dioxide dissolve in rainwater to form acid rain.
    Acid rain is highly corrosive and damages metallic structures, monuments and buildings.

    Reviewed By:
    Krishna Kant Majee
    M.Sc., B.Ed.

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