Fossil Fuel: Coal and Petroleum
High-yield AISSEE Class 9 General Science guide for Fossil Fuel: Coal and Petroleum (Section D • Topic 1). Contains pointwise theories, fractional distillation tables, carbon content mnemonics, solved examination models, and 10 practice drills.
Overview & Fundamental Concept
High-yield AISSEE Class 9 General Science guide for Fossil Fuel: Coal and Petroleum (Section D • Topic 1). Contains pointwise theories, fractional distillation tables, carbon content mnemonics, solved examination models, and 10 practice drills.
Official Syllabus Coverage Breakdown
| Syllabus Item | Prescribed Scope | Exam Relevance & Pedagogical Objective |
|---|---|---|
| Appendix-III Item 1 | Exhaustible vs inexhaustible resources, carbonisation, types of coal (Anthracite, Bituminous, Lignite, Peat), destructive distillation byproducts (Coke, Coal Tar, Coal Gas), petroleum origin, fractional distillation fractions and their boiling ranges, petrochemicals, natural gas (CNG/PNG), and PCRA guidelines. | Master the formation conditions, industrial distillation fractions, carbon percentages, chemical uses, and conservation strategies of fossil fuels for AISSEE Class IX. |
1. Natural Resources & Origin of Fossil Fuels
- Inexhaustible Natural Resources: Present in unlimited quantity in nature and are not likely to be exhausted by human activities. Examples: Sunlight, air, wind, rainfall.
- Exhaustible Natural Resources: Limited in quantity in nature and can be completely depleted by reckless human consumption. Examples: Forests, wildlife, minerals, coal, petroleum, natural gas.
- Definition of Fossil Fuels: Exhaustible fuels formed over millions of years (c. 300 million years ago during the Carboniferous period) from the dead and buried remains of living organisms under extreme temperature and pressure.
- Carbonisation: The slow geological process of conversion of dead vegetation into coal under high temperature and intense pressure in the absence of oxygen.
- Origin of Petroleum & Natural Gas: Formed from microscopic marine organisms (plankton, algae) that died and settled at the sea bed. Over millions of years, absence of air, high heat, and intense pressure transformed their organic remains into petroleum and natural gas trapped between non-porous impermeable rocks.
- World's First Oil Well: Drilled at Titusville, Pennsylvania, USA in 1859. In India, petroleum was first struck in 1867 at Makum (Assam). Prime Indian oil fields: Digboi (Assam), Bombay High (offshore Arabian Sea), and Godavari-Krishna river basins.
| Resource Classification | Natural Availability | Replenishment Rate | High-Yield AISSEE Examples |
|---|---|---|---|
| Inexhaustible Resources | Unlimited abundance in nature | Continuous & perpetual | Solar radiation, wind energy, tidal energy, atmospheric air |
| Exhaustible Resources (Renewable) | Replenishable under biological cycles | Decades to centuries (if conserved) | Fresh ground water, natural forests, wildlife species |
| Exhaustible Resources (Non-Renewable) | Strictly finite geological reserves | Millions of years (Rate of usage >> formation) | Coal, crude petroleum, compressed natural gas (CNG), radioactive uranium |
Cadet Mnemonic • 4 Ranks of Coal in Decreasing Carbon Content
Remember the 4 ranks of coal from highest carbon content to lowest using the phrase 'A Big Lion Prowls':
- A → Anthracite (90–95% Carbon, highest calorific value, smokeless, hard black)
- B → Bituminous (75–85% Carbon, common household & commercial coal, used for coking)
- L → Lignite (60–70% Carbon, soft brown coal, high moisture, used in thermal power plants)
- P → Peat (< 50% Carbon, lowest rank, first stage of coal formation, high smoke)
Exam Trick • Carbon Content vs Heat Energy Rule
Higher carbon percentage strictly correlates with higher calorific value and lower smoke emissions. Anthracite burns with a clean, short blue flame with virtually no soot, whereas Peat produces thick smoke and low thermal output.
AISSEE Trap Alert • Fossil Fuel Non-Renewability Trap
Fossil fuels CANNOT be prepared in a laboratory because the requisite physical conditions (millions of years of time, geological crust pressures, and biological scale) cannot be artificially duplicated. Never mark 'fossil fuels can be synthesised quickly in modern chemical labs' as True in AISSEE True/False MCQs!
2. Destructive Distillation of Coal & Industrial Byproducts
- Destructive Distillation: The industrial process of heating crushed coal strongly at high temperatures (approx. 1000°C) in the strict absence of air.
- 1. Coke: A tough, porous, and pure black solid residue. It contains nearly 98% pure carbon.
• Industrial Uses: Essential reducing agent in blast furnaces for smelting iron ore and steel; manufacturing of water gas (CO + H₂) and producer gas (CO + N₂). - 2. Coal Tar: A thick, black, viscous liquid having an unpleasant odor. It is a complex mixture of about 200 organic chemical compounds.
• Industrial Uses: Starting material for synthetic dyes, drugs, explosives (TNT), perfumes, plastics, paints, photographic chemicals, and naphthalene balls (used to repel moths and insects).
• Crucial Exam Fact: In modern highway construction, Bitumen (a petroleum fraction) has replaced coal tar for road metalling. - 3. Coal Gas: A gaseous fuel byproduct obtained during the processing of coal to get coke. It is a mixture of hydrogen (H₂), methane (CH₄), and carbon monoxide (CO).
• History: Used for street lighting for the first time in London in 1810 and New York around 1820. Today it is used primarily as an industrial heat source. - 4. Ammoniacal Liquor: Dissolves ammonia to produce ammonium sulfate, an essential nitrogenous agricultural fertilizer.
| Coal Byproduct | Physical State | Key Chemical Composition | Primary AISSEE Exam Application |
|---|---|---|---|
| Coke | Porous black solid | ~98% Elemental Carbon | Reducing agent in iron/steel metallurgy; clean smokeless fuel |
| Coal Tar | Viscous black liquid | Mixture of ~200 aromatic compounds | Production of naphthalene balls, synthetic dyes, perfumes, drugs |
| Coal Gas | Inflammable gas | H₂ (50%) + CH₄ (30%) + CO (10%) | Industrial fuel located near coal processing units |
| Ammoniacal Liquor | Aqueous solution | Ammonium hydroxide (NH₄OH) | Neutralised with sulfuric acid to make ammonium sulfate fertilizer |
Exam Trick • Naphthalene Balls Origin Trap
When examiners ask: 'Naphthalene balls used to repel moths are obtained from:' Options: (A) Petroleum, (B) Coal Tar, (C) Coke, (D) Coal Gas. Correct answer is (B) Coal Tar. Do NOT confuse it with paraffin wax from petroleum!
AISSEE Trap Alert • Bitumen vs Coal Tar Substitution
Traditionally coal tar was used for surfacing roads. Modern road metalling uses Bitumen, which is a petroleum refining byproduct, NOT a coal product.
3. Petroleum Refining & Fractional Distillation Fractions
- Crude Petroleum ('Black Gold'): A dark, thick, oily liquid with an unpleasant smell. Called 'Black Gold' due to its immense economic commercial value and the myriad industrial petrochemicals derived from it.
- Petroleum Refining: The process of separating the various constituents/fractions of petroleum according to their differences in boiling points. Carried out in tall fractional distillation columns in petroleum refineries.
- Temperature Gradient in Fractionating Column: The temperature decreases from the bottom of the tower to the top. Vapors with lower boiling points rise to the cooler top; fractions with higher boiling points condense at the hotter lower tiers.
- Liquefied Petroleum Gas (LPG): Boiling point < 40°C. Primary component is Butane (C₄H₁₀) with propane. Odorless gas made detectable by adding foul-smelling Ethyl Mercaptan (C₂H₅SH) for leak detection.
- Petrol (Gasoline): Boiling point 40°C–170°C. Motor fuel for light vehicles, aviation spirit, solvent for dry cleaning.
- Kerosene: Boiling point 170°C–250°C. Fuel for domestic wick stoves, pressure lamps, and purified aviation grade fuel for jet aircraft engines.
- Diesel: Boiling point 250°C–350°C. Fuel for heavy motor vehicles (trucks, buses, tractors), railway locomotives, and backup electric generators.
- Lubricating Oil: High boiling point viscous fraction used to reduce frictional wear and tear in machine joints.
- Paraffin Wax: White solid fraction used for candles, vaseline, skin ointments, wax paper, and matchstick coating.
- Bitumen: Non-volatile black solid residue used for road surfacing and waterproofing paints.
| Fraction of Petroleum | Boiling Range | Carbon Atom Count | Prescribed Commercial Application |
|---|---|---|---|
| Petroleum Gas (LPG) | Below 40°C | C₁ – C₄ | Domestic cylinder fuel for cooking; industrial heating |
| Petrol (Gasoline) | 40°C – 170°C | C₅ – C₁₀ | Fuel for cars/motorcycles; solvent for dry cleaning delicate clothes |
| Kerosene | 170°C – 250°C | C₁₁ – C₁₆ | Fuel for stoves and lamps; special jet engine propellant |
| Diesel | 250°C – 350°C | C₁₅ – C₁₈ | Fuel for heavy trucks, commercial buses, electric generators |
| Lubricating Oil | 350°C – 400°C | C₁₇ – C₂₀ | Mechanical lubrication of machine parts to reduce wear & tear |
| Paraffin Wax | Semi-solid residue | C₂₀ – C₃₀ | Ointments, cosmetics, candles, petroleum jelly (Vaseline) |
| Bitumen | Above 400°C (Bottom) | C₃₀ and above | Metalling asphalt roads, waterproofing membranes |
Cadet Mnemonic • Distillation Fractions from Top to Bottom
Remember the petroleum fractions in increasing boiling point order (top of tower to bottom) using 'Little Peter Kept Driving Large Purple Buses':
- L → LPG (Top fraction, lowest boiling point < 40°C)
- P → Petrol (40°–170°C)
- K → Kerosene (170°–250°C)
- D → Diesel (250°–350°C)
- L → Lubricating Oil (350°–400°C)
- P → Paraffin Wax (Semi-solid)
- B → Bitumen (Bottom residue, highest boiling point > 400°C)
Exam Trick • Aviation Fuel Identification
A frequent AISSEE trap asks which fraction powers jet aircraft. The correct answer is Kerosene (purified aviation turbine fuel), NOT petrol or diesel!
AISSEE Trap Alert • LPG Leakage Indicator
LPG itself is completely odorless. The characteristic pungent smell during gas leakage is caused by Ethyl Mercaptan, deliberately blended in minute quantities for disaster prevention.
4. Natural Gas, Petrochemicals & PCRA Conservation Protocols
- Natural Gas Composition: Consists predominantly of Methane (CH₄) (approx. 85–95%), along with small percentages of ethane and propane.
- Compressed Natural Gas (CNG): Natural gas compressed under high pressure (200–250 bar). Clean burning motor fuel producing negligible soot, carbon monoxide, and sulfur oxides. Distributed via pipelines as Piped Natural Gas (PNG) in cities like Delhi and Vadodara.
- Petrochemicals: Useful organic chemical substances derived from petroleum and natural gas. Used in manufacture of detergents, synthetic fibres (polyester, nylon, acrylic), and polythene.
- Hydrogen Gas from Natural Gas: Obtained by steam cracking of natural gas; critical raw material for the manufacture of nitrogenous fertilizers (Urea).
- PCRA (Petroleum Conservation Research Association) Guidelines:
• Drive vehicles at a constant and moderate speed.
• Switch off the engine at traffic lights or during waiting intervals.
• Ensure correct tyre pressure (under-inflated tyres waste 5–10% fuel).
• Ensure regular vehicle maintenance and engine tuning.
| Gaseous Fuel | Primary Component | Storage State | Key Advantage |
|---|---|---|---|
| CNG (Compressed Natural Gas) | Methane (CH₄) ~90% | Compressed gas at 200–250 atm | Produces zero lead/sulfur emissions, non-corrosive |
| LPG (Liquefied Petroleum Gas) | Butane (C₄H₁₀) + Propane | Liquefied under moderate pressure in steel cylinders | High calorific value (55,000 kJ/kg), easy household usage |
| PNG (Piped Natural Gas) | Methane (CH₄) | Piped low pressure gas | Eliminates need for cylinder transport, unbroken supply |
Exam Trick • CNG vs LPG Primary Hydrocarbon
CNG starts with C → Methane (1 Carbon). LPG starts with L → Butane (4 Carbons). Remember: CNG is Methane; LPG is Butane.
AISSEE Trap Alert • Environmental Acid Rain Warning
Combustion of coal and diesel releases sulfur dioxide (SO₂) and nitrogen oxides (NO₂), which dissolve in atmospheric rainwater to produce highly corrosive acid rain (H₂SO₄ and HNO₃).
Visual Concept Blueprint • Vector Architecture
Speed Shortcuts & Concept Mastery Strategies
Master these high-yield heuristics curated by top AISSEE scorers to eliminate confusion and answer questions accurately in under 45 seconds.
Shortcut Technique 1: The Volatility-Boiling Point Inverse Rule
In any distillation column, the most volatile component with the lowest boiling point emerges at the highest level (LPG at the top), while the heaviest hydrocarbon with the highest boiling point condenses at the bottom (Bitumen at the base).
Shortcut Technique 2: Eliminating Coal Product Confusions
Check the physical state: Coke is solid (98% carbon); Coal Tar is liquid (~200 aromatic chemicals); Coal Gas is gas (fuel). Bitumen is a petroleum byproduct, NOT a coal byproduct.
Shortcut Technique 3: Hydrocarbon Formula Association
LPG is primarily Butane ($C_4H_{10}$); Natural Gas / CNG is primarily Methane ($CH_4$). Remembering this 1-carbon vs 4-carbon split solves 90% of fuel composition questions instantly.
Interactive 3D Revision Flashcards Deck
Click any card to flip and reveal the key exam rule or memory anchor.
REVISION FLASHCARD
What is the process of converting dead vegetation into coal under high pressure and temperature called?
CADET MEMORY KEY
Carbonisation (takes millions of years under anaerobic crust conditions).
REVISION FLASHCARD
Which byproduct of coal destructive distillation contains nearly 98% carbon and acts as a metallurgical reducing agent?
CADET MEMORY KEY
Coke (used extensively in blast furnaces for smelting steel and iron).
REVISION FLASHCARD
Which petroleum fraction is specifically used as fuel for jet aircraft engines?
CADET MEMORY KEY
Purified Kerosene (Aviation Turbine Fuel / ATF).
REVISION FLASHCARD
What foul-smelling chemical compound is added to LPG cylinders to detect gas leakages?
CADET MEMORY KEY
Ethyl Mercaptan ($C_2H_5SH$), an organosulfur compound.
Common Traps & Examination Pitfalls
Avoid the Speed-Guess Trap: Under AISSEE pressure, candidates frequently misread question stems containing negative qualifiers ('NOT', 'EXCEPT', 'INCORRECT'). Always circle negative keywords in your question booklet before selecting an answer choice on your OMR sheet.
Key Principles & Scientific Identities
General Combustion of Methane (Natural Gas)
$$CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O + \text{Heat Energy (890 kJ/mol)}$$
Complete combustion of methane yields harmless water vapor, carbon dioxide, and maximum thermal energy.
Destructive Distillation Balance
$$\text{Coal} \xrightarrow[\text{absence of air}]{\Delta \approx 1000^\circ\text{C}} \text{Coke (Solid)} + \text{Coal Tar (Liquid)} + \text{Coal Gas (Gas)}$$
Thermal decomposition of coal in closed anaerobic retorts.
Step-by-Step Solved Examination Models
Solved Example 1
Model Problem
Which variety of coal has the highest percentage of carbon content and burns with the least amount of smoke?
Detailed Solution:
Anthracite is the highest metamorphic grade of coal, containing 90% to 95% carbon. It possesses the highest calorific value, burns with a clean short blue flame, and produces virtually no smoke.
Solved Example 2
Model Problem
A petroleum product used in place of coal tar for metalling the surface of roads is:
Detailed Solution:
Bitumen, the heavy non-volatile residue from petroleum fractional distillation, has completely replaced coal tar for macadamizing and metalling road surfaces due to its superior water-binding durability.
Solved Example 3
Model Problem
Naphthalene balls used as moth repellents in domestic wardrobes are industrially obtained from:
Detailed Solution:
Coal tar is a complex mixture of about 200 chemical substances. Fractional distillation of coal tar yields naphthalene, which is pressed into mothballs to protect woollen garments from insect larvae.
AISSEE High-Yield Practice Drills (10 Questions)
Simulated exam drill matching NTA question style, difficulty, and phrasing. Click an option for instant feedback and pedagogical explanation.
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Question 1 of 10
Exam Standard
Which of the following natural resources is an inexhaustible natural resource?
Correct Answer: Option (C)
Sunlight is available in unlimited amounts in nature and cannot be exhausted by human activity, making it inexhaustible.
Question 2 of 10
Exam Standard
The slow conversion of dead vegetation into coal under geological conditions is termed:
Correct Answer: Option (A)
The geological decomposition of plant matter into coal under high pressure and temperature over millions of years is called carbonisation.
Question 3 of 10
Tricky
The first commercial oil well in the world was drilled in 1859 at:
Correct Answer: Option (B)
The world's first oil well was drilled in Titusville, Pennsylvania in 1859. The first Indian oil well was drilled in Makum, Assam in 1867.
Question 4 of 10
Exam Standard
Which of the following is an almost pure form of elemental carbon obtained from coal?
Correct Answer: Option (B)
Coke contains nearly 98% pure carbon, making it the purest elemental form of carbon produced from coal destructive distillation.
Question 5 of 10
Exam Standard
The constituent of petroleum used for making ointments, candles, and vaseline is:
Correct Answer: Option (B)
Paraffin wax is a semi-solid petroleum byproduct used in the manufacture of cosmetics, candles, ointments, and petroleum jelly (Vaseline).
Question 6 of 10
Exam Standard
The primary constituent gas present in Compressed Natural Gas (CNG) is:
Correct Answer: Option (D)
Natural gas and CNG consist of approximately 85% to 95% Methane (CH4), making Methane the principal gaseous component.
Question 7 of 10
Tricky
Which of the following petroleum fractions is arranged in INCORRECT order of boiling points (from lowest to highest)?
Correct Answer: Option (C)
Option C is inverted. The true ascending order of boiling point is LPG (<40°C) < Petrol (40-170°C) < Kerosene (170-250°C) < Diesel (250-350°C).
Question 8 of 10
Hard
Coal gas was first utilized for commercial municipal street lighting in London in the year:
Correct Answer: Option (A)
Coal gas was used for street lighting for the first time in London in 1810 and later in New York in 1820.
Question 9 of 10
Exam Standard
Which organisation in India advises citizens on methods to conserve petrol and diesel while driving?
Correct Answer: Option (B)
PCRA stands for Petroleum Conservation Research Association, an Indian statutory body promoting fuel conservation protocols.
Question 10 of 10
Tricky
Match the following petroleum fractions with their uses:
1. Bitumen — (p) Jet aircraft fuel
2. Kerosene — (q) Road surfacing
3. Petrol — (r) Dry cleaning solvent
Which combination is correct?
1. Bitumen — (p) Jet aircraft fuel
2. Kerosene — (q) Road surfacing
3. Petrol — (r) Dry cleaning solvent
Which combination is correct?
Correct Answer: Option (B)
Bitumen is used for road surfacing (1-q), Kerosene as fuel for jet engines/stoves (2-p), and Petrol as solvent for dry cleaning (3-r).
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Last-Minute Cadet Revision Matrix
Rapid recall checkpoints to review 24 hours before stepping into the examination hall.
| Concept Checkpoint | High-Yield Exam Rule & Memory Anchor |
|---|---|
| Checkpoint 1 | Sun/Wind/Air = Inexhaustible; Coal/Petroleum/Minerals = Exhaustible (finite reserves). |
| Checkpoint 2 | Anthracite (>90% C) > Bituminous (75–85% C) > Lignite (60–70% C) > Peat (<50% C). |
| Checkpoint 3 | Absence of air at ~1000°C yields Coke (solid reducer), Coal Tar (~200 chemicals), Coal Gas (fuel). |
| Checkpoint 4 | LPG (<40°C) → Petrol → Kerosene → Diesel → Lubricating Oil → Wax → Bitumen (>400°C). |
| Checkpoint 5 | Always Purified Kerosene (Aviation Turbine Fuel), never petrol. |
| Checkpoint 6 | Chief component is Methane ($CH_4$). LPG is primarily Butane ($C_4H_{10}$). |
Frequently Asked Questions
Why are coal and petroleum referred to as fossil fuels?
They are formed over hundreds of millions of years from the buried, decomposed remains (fossils) of prehistoric plants and aquatic organisms under immense heat and pressure in the Earth's crust.
What is the difference between destructive distillation and fractional distillation?
Destructive distillation involves heating a complex solid (like coal) in the absence of air to chemically decompose it into new substances (coke, tar, gas). Fractional distillation physically separates a liquid mixture (like crude petroleum) into fractions based on differing boiling points without chemical decomposition.
Why is petroleum called 'Black Gold'?
Crude petroleum is black when extracted from underground reservoirs. Because almost all modern transportation, lubricants, plastics, fertilizers, and pharmaceuticals depend on its commercial fractions, its enormous economic worth is likened to gold.
What is the advantage of using CNG over petrol or diesel?
CNG burns almost completely with minimal unburnt hydrocarbon residue, emits negligible carbon monoxide and soot, produces no sulfur or lead emissions, and causes significantly less engine corrosion.
Why has Bitumen replaced Coal Tar for surfacing roads?
Bitumen is more resistant to weathering, provides stronger adhesion to gravel aggregates, does not become overly brittle in winter or sticky in summer, and is less toxic than aromatic coal tar.