Class 8 General Science Chapter 4 Question Answer | Coal and Petroleum | English Medium | ASSEB

Coal and Petroleum

Welcome to HSLC Guru! In this lesson on Chapter 4 — Coal and Petroleum from the ASSEB Class 8 General Science textbook, you will learn about the natural resources that power our daily lives. We have prepared a clear summary, complete textbook question answers, additional MCQs, fill in the blanks, true or false statements, and a glossary table — all written in simple English to help you score full marks in your exams.

Summary of the Chapter

The materials present in nature that are useful to us are called natural resources. Some natural resources are present in unlimited amounts in nature and are called inexhaustible natural resources, for example, sunlight, air, and water. Other resources are present in limited amounts in nature, and once used, they cannot be replaced quickly. These are called exhaustible natural resources, for example, coal, petroleum, natural gas, forests, and wildlife. Coal, petroleum, and natural gas are known as fossil fuels because they are formed from the dead remains of plants and animals that lived millions of years ago, buried deep under the earth.

Coal is a hard black substance used as a fuel in homes and industries. About 300 million years ago, dense forests in low-lying wetlands got buried under the soil due to natural processes like floods and earthquakes. Under high temperature and pressure inside the earth, the dead plants slowly converted into coal. This slow process of converting dead vegetation into coal is called carbonisation. There are four main types of coal — peat (lowest carbon content), lignite, bituminous, and anthracite (highest carbon content). When coal is heated in the absence of air (a process called destructive distillation), it gives three useful products: coke (a tough, porous black fuel used in steel making), coal tar (a black thick liquid used to make dyes, drugs, paints, perfumes, plastics, photographic materials, etc.), and coal gas (used as a fuel in factories near coal processing plants).

Petroleum is a dark oily liquid found between the layers of rocks under the sea bed. It was formed from the dead remains of tiny sea plants and animals that got buried under the sea many millions of years ago. The petroleum extracted from oil wells is called crude oil and is a mixture of many useful substances. The process of separating these different substances from petroleum by heating it to different temperatures in a refinery is called refining, and is done by fractional distillation. The various useful products obtained from petroleum are petroleum gas (LPG) used as cooking fuel, petrol used as motor and aviation fuel, diesel used in heavy vehicles and generators, kerosene used for stoves and jet aircraft, lubricating oil used in machines, paraffin wax used in candles and ointments, and bitumen used for road surfacing. Because petroleum gives so many useful products, it is called “black gold”.

Natural gas is a clean fossil fuel found above petroleum deposits. It can be easily transported through pipes. When stored under high pressure, it is called Compressed Natural Gas (CNG). CNG is used to generate electricity, as a fuel in vehicles, and as a starting material for fertilisers and chemicals. Since fossil fuels take millions of years to form and are present in limited amounts, we must conserve them. The Petroleum Conservation Research Association (PCRA) advises drivers to: drive at a constant moderate speed, switch off the engine at traffic lights, keep tyres properly inflated, and ensure regular maintenance of vehicles to save fuel. Using public transport, cycling, and turning off lights and electrical appliances when not in use also helps to conserve these precious natural resources for future generations.

Textbook Question Answers

1 Mark Questions

Q1. What is a natural resource?

Answer: The materials which are obtained from nature and are useful to us are called natural resources.

Q2. Name two inexhaustible natural resources.

Answer: Sunlight and air are two inexhaustible natural resources.

Q3. Name the three fossil fuels.

Answer: Coal, petroleum, and natural gas are the three fossil fuels.

Q4. What is carbonisation?

Answer: The slow process of conversion of dead vegetation into coal under high temperature and pressure is called carbonisation.

Q5. Why is petroleum called “black gold”?

Answer: Petroleum is called “black gold” because it is a dark coloured liquid that gives many valuable products like petrol, diesel, kerosene, etc., which are very precious like gold.

Q6. What is the full form of CNG and LPG?

Answer: CNG stands for Compressed Natural Gas, and LPG stands for Liquefied Petroleum Gas.

Q7. Name the type of coal that has the highest carbon content.

Answer: Anthracite is the type of coal that has the highest carbon content.

Q8. What is coke used for?

Answer: Coke is used in the manufacture of steel and in the extraction of many metals.

Q9. What is the full form of PCRA?

Answer: PCRA stands for Petroleum Conservation Research Association.

Q10. Name the product of petroleum used in road surfacing.

Answer: Bitumen is the product of petroleum used in road surfacing.

2-3 Marks Questions

Q1. Differentiate between exhaustible and inexhaustible natural resources with examples.

Answer: Exhaustible natural resources are those which are present in limited amounts in nature and can be exhausted by human use, for example, coal, petroleum, and natural gas. Inexhaustible natural resources are those which are present in unlimited amounts in nature and are not likely to be exhausted by human use, for example, sunlight, air, and water.

Q2. What are the four types of coal? Arrange them in order of increasing carbon content.

Answer: The four types of coal are peat, lignite, bituminous, and anthracite. In order of increasing carbon content, they are arranged as: Peat < Lignite < Bituminous < Anthracite. Peat has the lowest carbon content, while anthracite has the highest carbon content.

Q3. What is destructive distillation? Name the products obtained when coal undergoes destructive distillation.

Answer: The process of heating coal in the absence of air is called destructive distillation. The three useful products obtained are: (i) Coke — a tough, porous black solid, (ii) Coal tar — a black, thick liquid with an unpleasant smell, and (iii) Coal gas — a fuel gas used in industries.

Q4. What is petroleum refining? Why is it necessary?

Answer: The process of separating different useful substances from petroleum (crude oil) by heating it at different temperatures in a refinery is called petroleum refining. It is necessary because crude oil is a dark coloured mixture of many substances. These substances must be separated to obtain useful products like petrol, diesel, kerosene, lubricating oil, etc.

Q5. Mention any three uses of natural gas (CNG).

Answer: Three uses of natural gas (CNG) are: (i) It is used as a fuel for transport vehicles like buses, taxis, and cars because it causes less pollution. (ii) It is used to generate electricity in power plants. (iii) It is used as a starting material for the manufacture of chemicals and fertilisers.

Q6. Why should we conserve fossil fuels? Mention two ways.

Answer: Fossil fuels (coal, petroleum, and natural gas) take millions of years to form and are present in limited amounts in nature. Once used up, they cannot be replaced quickly, so they must be conserved. Two ways to conserve fossil fuels are: (i) Use public transport, bicycle, or walk for short distances instead of personal vehicles. (ii) Switch off lights, fans, and other electrical appliances when not in use.

5-6 Marks Questions

Q1. Explain the formation of coal in nature.

Answer: About 300 million years ago, the earth had dense forests in the low-lying wetland areas. Due to natural processes like floods, storms, and earthquakes, these forests got buried under the soil. As more soil deposited over them, the dead plants got compressed deep inside the earth. As they went deeper and deeper, they were exposed to high temperature and high pressure inside the earth. Under these conditions, the dead vegetation slowly converted into coal over millions of years. Since coal contains mainly carbon, this slow process of conversion of dead plants into coal is called carbonisation. Because coal was formed from the remains of living organisms (plants), it is called a fossil fuel.

Q2. Describe the formation and refining of petroleum.

Answer: Petroleum was formed from the dead remains of tiny sea plants and animals (organisms) that lived millions of years ago. When these organisms died, their bodies sank to the bottom of the sea and got covered with mud and sand. Over millions of years, in the absence of air and under the action of high temperature, high pressure and certain bacteria, the dead organisms got slowly converted into petroleum and natural gas. Petroleum is found between the layers of rocks under the sea bed. The petroleum extracted from oil wells is called crude oil, which is a dark coloured oily liquid mixture of many substances. The process of separating the various useful substances from petroleum is called refining, and is carried out in petroleum refineries by the method of fractional distillation. In this method, crude oil is heated and the various components like petrol, diesel, kerosene, lubricating oil, etc., separate out at different temperatures based on their boiling points.

Q3. Write down the various useful products obtained from petroleum and their uses.

Answer: The various useful products obtained from petroleum and their uses are:

Petroleum gas (LPG): Used as fuel for cooking in homes and as fuel in industries.
Petrol: Used as motor fuel for cars, motorcycles, and as aviation fuel for small aircraft.
Diesel: Used as fuel for heavy motor vehicles like trucks, buses, tractors, and in electric generators.
Kerosene: Used as a fuel for stoves, lamps, and as fuel for jet aircraft.
Lubricating oil: Used for lubricating moving parts of machines.
Paraffin wax: Used in making candles, vaseline, and ointments.
Bitumen: Used to surface roads and for water-proofing.

Q4. What are the tips given by PCRA to save petrol and diesel while driving?

Answer: The Petroleum Conservation Research Association (PCRA) advises the following tips to save petrol and diesel while driving:

Drive at a constant and moderate speed as far as possible.
Switch off the engine of the vehicle at traffic lights or at any place where you have to wait.
Ensure correct tyre pressure of the vehicle, as low pressure increases fuel consumption.
Get the engine of the vehicle checked and serviced regularly to ensure efficient working.
Avoid sudden acceleration and frequent braking.
Use public transport whenever possible.

Q5. Distinguish between coke, coal tar, and coal gas.

Answer: Coke, coal tar, and coal gas are the three useful products obtained when coal is processed by destructive distillation.

Coke: It is a tough, porous, and black solid substance. It is almost pure form of carbon. It is used in the manufacture of steel and in the extraction of many metals from their ores.
Coal tar: It is a black, thick liquid with an unpleasant smell. It is a mixture of about 200 substances. The products obtained from coal tar are used as starting materials for making dyes, drugs, explosives, paints, perfumes, plastics, photographic materials, roofing materials, etc. Naphthalene balls used to repel moths are also obtained from coal tar.
Coal gas: It is a fuel gas obtained during the processing of coal to get coke. It is used as a fuel in many industries situated near coal processing plants.

Additional Multiple Choice Questions (MCQs)

Q1. Which of the following is an inexhaustible natural resource?
(a) Coal (b) Petroleum (c) Sunlight (d) Natural gas

Answer: (c) Sunlight

Q2. Coal, petroleum, and natural gas are called:
(a) Solar fuels (b) Fossil fuels (c) Bio fuels (d) Nuclear fuels

Answer: (b) Fossil fuels

Q3. Which of the following types of coal has the lowest carbon content?
(a) Anthracite (b) Bituminous (c) Lignite (d) Peat

Answer: (d) Peat

Q4. Petroleum is called:
(a) Black diamond (b) Black gold (c) White gold (d) Liquid gold

Answer: (b) Black gold

Q5. Which product of petroleum is used as fuel in jet aircraft?
(a) Petrol (b) Diesel (c) Kerosene (d) LPG

Answer: (c) Kerosene

Q6. The slow process of conversion of dead vegetation into coal is called:
(a) Refining (b) Carbonisation (c) Distillation (d) Fractionation

Answer: (b) Carbonisation

Q7. Which of the following is used in road surfacing?
(a) Bitumen (b) Paraffin wax (c) Lubricating oil (d) Petrol

Answer: (a) Bitumen

Q8. Which fossil fuel causes the least pollution when burnt in vehicles?
(a) Coal (b) Petrol (c) Diesel (d) CNG

Answer: (d) CNG

Q9. Coke is used mainly in the manufacture of:
(a) Plastic (b) Steel (c) Paper (d) Glass

Answer: (b) Steel

Q10. The full form of LPG is:
(a) Liquid Propane Gas (b) Liquefied Petroleum Gas (c) Light Petroleum Gas (d) Local Petrol Gas

Answer: (b) Liquefied Petroleum Gas

Fill in the Blanks

Q1. Coal, petroleum, and natural gas are called __________ fuels.

Answer: fossil

Q2. The process of separating useful substances from petroleum is called __________.

Answer: refining

Q3. __________ is the type of coal with the highest carbon content.

Answer: Anthracite

Q4. __________ is used in making candles and ointments.

Answer: Paraffin wax

Q5. The full form of CNG is __________.

Answer: Compressed Natural Gas

True or False

Q1. Sunlight is an exhaustible natural resource.

Answer: False. Sunlight is an inexhaustible natural resource.

Q2. Coal is formed from the dead remains of sea organisms.

Answer: False. Coal is formed from the dead remains of land vegetation (plants), while petroleum is formed from sea organisms.

Q3. Bitumen is used in the construction of roads.

Answer: True.

Q4. CNG is more polluting than petrol.

Answer: False. CNG is less polluting than petrol and diesel.

Q5. Coke is almost a pure form of carbon.