"Coal and Petroleum" for Class 8 Science (CBSE):-

Extra 20 important long questions and answers from the chapter:3

 

1. What is coal? How is it formed?

Ans: Coal is a fossil fuel that is black in colour and is used as a source of energy.

Formation of Coal:

Millions of years ago, dense forests in low-lying wetland areas got buried under soil.

Due to high temperature and pressure, these plant remains slowly converted into coal.

This slow process of conversion is called carbonization.

Coal mainly consists of carbon along with hydrogen, oxygen, sulphur, and nitrogen.

Coal is used in power plants, industries, and domestic cooking.

It is a non-renewable resource as it takes millions of years to form.

 

2. What are the different types of coal? Explain.

Ans: Coal is classified into different types based on carbon content and energy output.

Anthracite – Highest carbon content (about 80-90%), burns with high heat, and is the cleanest coal.

Bituminous – Most commonly used, contains 60-80% carbon, used in power plants and industries.

Lignite – Lower carbon content (45-55%), produces more smoke, used in electricity generation.

Peat – Least carbon content (less than 40%), not efficient as a fuel, found in the early stage of coal formation.

These types differ in energy efficiency, pollution level, and industrial usage.

 

3. What are the different products obtained from coal? Give their uses.

Ans: Coal is processed to obtain various products used in industries and households.

Coke – A porous, black substance used in steel manufacturing and metal extraction.

Coal Tar – A thick, black liquid used in making roads, synthetic dyes, drugs, and waterproof paints.

Coal Gas – Used as an industrial fuel for heating and lighting.

Ammonia Liquor – Used in the production of fertilizers.

Carbon Black – Used in printing ink, rubber, and tire manufacturing.

These products are used in construction, chemical, and fuel industries.

 

4. What is petroleum? How is it formed?

Ans: Petroleum is a liquid fossil fuel that is an important energy source.

Formation of Petroleum:

Formed from dead marine organisms buried under layers of sand and silt millions of years ago.

Due to heat and pressure, these remains converted into crude oil.

This oil is extracted through oil wells and refined in petroleum refineries.

Petroleum is a mixture of hydrocarbons like petrol, diesel, and kerosene.

It is also known as "black gold" due to its high economic value.

Used in transportation, industries, and manufacturing of chemicals and plastics.

 

5. What is fractional distillation? Explain the various fractions obtained from petroleum.

Ans: Fractional distillation is a process of separating crude oil into different useful components based on their boiling points.

Fractions obtained from petroleum:

Petroleum Gas (LPG) – Used as cooking fuel.

Petrol – Used in cars, motorcycles, and aviation fuel.

Kerosene – Used as jet fuel and cooking fuel.

Diesel – Used in buses, trucks, and power generators.

Lubricating Oil – Used in machines and engines.

Bitumen – Used for paving roads and waterproofing.

 

6. What is natural gas? What are its uses?

Ans: Natural gas is a fossil fuel found underground along with petroleum.

Uses of Natural Gas:

Compressed Natural Gas (CNG) – Used as a clean fuel in vehicles.

Liquefied Petroleum Gas (LPG) – Used as domestic cooking fuel.

Power generation – Used in gas turbines to generate electricity.

Industrial use – Used in the manufacture of fertilizers, chemicals, and glass.

Eco-friendly – Produces less pollution compared to coal and petroleum.

Easily transportable – Supplied through pipelines to households and industries.

 

7. Why is petroleum called "black gold"?

Ans: Petroleum is called "black gold" because:

It has high economic value due to its widespread use.

It is used to make fuel (petrol, diesel, kerosene).

Used in transportation, electricity generation, and industries.

Used in chemical and plastic industries to make paints, wax, and detergents.

It is scarce and expensive like gold.

Extracted in the form of crude oil, which is black in colour.

 

8. How does the burning of fossil fuels affect the environment?

Ans: The burning of fossil fuels causes several environmental issues:

Air pollution – Releases harmful gases like CO₂, SO₂, and NO₂.

Global warming – Increases greenhouse gases, leading to climate change.

Acid rain – Sulfur dioxide and nitrogen oxides mix with rain, damaging crops and buildings.

Smog formation – Reduces visibility and affects health.

Oil spills – Contaminate water bodies, harming marine life.

Deforestation – Land clearing for mining and drilling causes habitat loss.

 

9. How can we conserve fossil fuels?

Ans: Fossil fuels are limited, so we must use them wisely.

Use public transport instead of private vehicles.

Switch off electrical appliances when not in use.

Use alternative energy sources like solar, wind, and hydro energy.

Improve fuel efficiency in vehicles and industries.

Reduce, Reuse, and Recycle plastic products.

Use biofuels like ethanol and biodiesel as substitutes.

 

10. What are petrochemicals? Give their uses.

Ans: Petrochemicals are chemicals derived from petroleum and natural gas.

Uses of Petrochemicals:

Plastics – Used in bottles, containers, and packaging.

Synthetic fibers – Used in clothes, ropes, and carpets.

Fertilizers – Made from petroleum derivatives like ammonia.

Rubber and tires – Used in automobiles.

Cosmetics and medicines – Used in perfumes, lotions, and pharmaceutical products.

Detergents – Used in cleaning agents and shampoos.

 

11. What are fossil fuels? Why are they considered non-renewable?

Ans: Fossil fuels are natural fuels formed from the remains of plants and animals buried under the Earth's surface for millions of years.

Examples: Coal, Petroleum, and Natural Gas.

Why are they non-renewable?

Takes millions of years to form.

Limited in nature and cannot be replaced quickly.

Overuse leads to depletion of resources.

Cannot be artificially created on a large scale.

Demand is increasing, but supply is decreasing.

Burning fossil fuels harms the environment.

 

12. What are the disadvantages of using fossil fuels?

Ans: Using fossil fuels has many negative effects:

Causes air pollution – Releases CO₂, SO₂, and NO₂ gases.

Leads to global warming – CO₂ traps heat, increasing Earth’s temperature.

Causes acid rain – Sulphur dioxide mixes with rainwater, damaging crops and buildings.

Non-renewable – Once exhausted, they cannot be replaced.

Oil spills – Harm marine life and pollute water bodies.

Leads to respiratory diseases – Causes asthma, lung infections, and breathing issues.

 

13. How does fractional distillation of petroleum work?

Ans: Fractional distillation is the process of separating petroleum into different useful components based on their boiling points.

Process:

Crude oil is heated in a distillation column.

Different components evaporate at different temperatures.

The vapors rise and cool down at different heights.

Heavier fractions (bitumen, diesel) condense at the bottom.

Lighter fractions (petrol, kerosene) condense higher up.

The separated components are used in fuels, industries, and chemicals.

 

14. What are the advantages of using natural gas over other fossil fuels?

Ans: Natural gas is a cleaner and efficient fuel compared to coal and petroleum.

Advantages:

Produces less pollution – Emits fewer harmful gases.

High calorific value – Provides more energy per unit.

Easy to transport – Supplied through pipelines.

No residue or smoke – Does not produce ash or soot.

Used as a fuel in CNG vehicles – Reduces vehicular pollution.

Used in industries – For manufacturing chemicals and fertilizers.

 

15. What are the differences between renewable and non-renewable resources?

Ans:

Feature	Renewable Resources	Non-Renewable Resources
Definition	Can be replenished naturally	Limited and take millions of years to form
Examples	Sunlight, Wind, Water	Coal, Petroleum, Natural Gas
Availability	Unlimited supply	Limited in nature
Environmental Impact	Eco-friendly	Causes pollution
Usage	Used in solar, wind, and hydroelectric power	Used as fuel for transport and industries
Sustainability	Can be used forever	May get exhausted

 

16. What is acid rain? How is it caused by burning fossil fuels?

Ans: Acid rain is rainfall that contains harmful acids like sulfuric acid and nitric acid.

Causes:

Burning fossil fuels releases sulphur dioxide (SO₂) and nitrogen oxides (NO₂).

These gases mix with water vapor in the atmosphere.

They form sulfuric acid (H₂SO₄) and nitric acid (HNO₃).

These acids fall with rain, damaging the environment.

Affects crops, water bodies, and historical monuments.

Example: Acid rain has damaged the Taj Mahal in India.

 

17. Why should we reduce the use of fossil fuels?

Ans: Fossil fuels should be conserved to protect the environment and future generations.

Reasons:

Non-renewable – Once exhausted, they cannot be replaced.

Causes air pollution – Releases harmful gases.

Leads to global warming – Increases Earth’s temperature.

Causes acid rain – Harms agriculture and buildings.

Creates health problems – Leads to breathing issues.

Alternative energy sources are available – Solar, wind, and hydroelectric power can replace fossil fuels.

 

18. What are the uses of bitumen?

Ans: Bitumen is a thick, black, and sticky substance obtained from petroleum.

Uses:

Road construction – Used to make asphalt roads.

Roofing material – Used for waterproofing houses.

Sealing cracks – Used in pipelines and walls.

Soundproofing – Used in buildings to reduce noise.

Paint and coatings – Used in protective paints.

Industrial use – Used in making adhesives and insulation materials.

 

19. How does mining coal affect the environment?

Ans: Coal mining has serious environmental impacts.

Effects of Coal Mining:

Deforestation – Large areas of forests are cleared for mining.

Soil erosion – Removes topsoil, making land infertile.

Water pollution – Toxic chemicals from mines enter water bodies.

Air pollution – Releases coal dust, causing lung diseases.

Loss of habitat – Destroys homes of wildlife.

Land degradation – Makes land unsuitable for farming.

 

20. How can we promote the use of alternative energy sources?

Ans: Alternative energy sources can reduce our dependence on fossil fuels.

Ways to Promote Alternative Energy:

Government policies – Provide incentives for renewable energy projects.

Solar panels – Use solar energy for electricity and heating.

Wind energy – Install wind turbines for power generation.

Hydroelectricity – Increase the use of water dams for electricity.

Public awareness – Educate people about renewable energy.

Reduce fossil fuel use – Use bicycles, public transport, and energy-efficient appliances.