What are the main types of fuels studied in Cambridge IGCSE Organic Chemistry?

In Cambridge IGCSE Organic Chemistry, the main types of fuels studied include fossil fuels such as coal, oil, and natural gas. These are primarily composed of hydrocarbons and are used extensively for energy production. Additionally, biofuels, which are derived from biological materials, are also discussed as renewable energy sources.

How are fossil fuels formed and what is their significance in Organic Chemistry?

Fossil fuels are formed from the remains of ancient plants and animals that were buried under layers of sediment millions of years ago. Over time, heat and pressure transformed these remains into coal, oil, and natural gas. In Organic Chemistry, they are significant because they are rich sources of hydrocarbons, which are fundamental compounds in the study of organic molecules and reactions.

What are the environmental impacts of using fossil fuels?

The use of fossil fuels has several environmental impacts, including the release of carbon dioxide and other greenhouse gases, which contribute to global warming and climate change. Burning fossil fuels also releases pollutants such as sulfur dioxide and nitrogen oxides, leading to air pollution and acid rain. These issues are critical topics in both environmental science and chemistry education.

What are biofuels and how do they differ from fossil fuels?

Biofuels are renewable energy sources derived from biological materials such as plants and animal waste. Unlike fossil fuels, which take millions of years to form, biofuels can be produced relatively quickly. They are considered more sustainable because they can be replenished and typically produce fewer greenhouse gases when burned. In Organic Chemistry, biofuels are studied as alternatives to traditional fossil fuels.

Why is the study of fuels important in the Cambridge IGCSE Chemistry curriculum?

The study of fuels is important in the Cambridge IGCSE Chemistry curriculum because it helps students understand the chemical principles behind energy production and consumption. It also highlights the role of chemistry in addressing global challenges such as energy sustainability and environmental protection. By learning about fuels, students gain insights into both the benefits and drawbacks of different energy sources, preparing them for further studies and informed decision-making.

Why is "Putting bitumen at the top of the tower" a common mistake in Fuels?

Why it happens: Inverting the gradient. How to avoid it: BITUMEN (heavy, high b.p.) at the BOTTOM. Refinery gas (light, low b.p.) at the TOP. Source: 0620/42 — recurring

Why is "Producing only CO₂ in incomplete combustion" a common mistake in Fuels?

Why it happens: Defaulting to complete. How to avoid it: Incomplete: CO and/or C (soot) — NOT CO₂.

Why is "Failing to balance combustion equations" a common mistake in Fuels?

Why it happens: Forgetting H atoms. How to avoid it: Balance C, then H, then O. The O₂ coefficient may need to be a fraction.

Organic ChemistryCambridge IGCSE Chemistry 0620 Extended

Fuels

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Fuels — Cambridge IGCSE 0620 Chemistry Extended (2026)

Coal, oil, gas, biofuels, hydrogen. Fractional distillation of crude oil and uses of each fraction. Plus combustion equations and pollution.

What you’ll learn

Mapped to the Cambridge IGCSE 0620 syllabus (2026-2028).

13.2 — Describe fossil fuels and the fractional distillation of crude oil.
13.2 — Name the fractions of petroleum and their uses.
13.2 — Write equations for combustion reactions.
13.2 — Distinguish fossil fuels and biofuels.

Fossil fuels

Coal, oil, gas — formed over millions of years from dead organisms. Non-renewable.

Fossil fuels are natural fuels formed from the remains of long-dead plants and animals, compressed and heated underground over millions of years.

Three big ones.

Coal: from ancient plants. Mostly carbon. Burned for electricity, steel-making.
Crude oil (petroleum): from ancient marine organisms. Mixture of hydrocarbons. Source of fuels and petrochemicals.
Natural gas: mostly methane (CH₄). Often found alongside oil.

Why "fossil"? Fossils = preserved remains of ancient life. Coal seams sometimes have fossilised plant imprints; oil drilling often turns up shells, plankton fragments.

Why non-renewable? Formed at GEOLOGICAL timescales (millions of years). We're using them at MUCH faster rates → reserves are finite.

Pollution. Combustion produces CO₂ (greenhouse gas) and may produce SO₂, NOₓ, CO, particulates. (See Air study note.)

Coal, crude oil, natural gas.
From ancient organic matter.
Non-renewable on human timescales.
Combustion → CO₂ + (sometimes) SO₂, NOₓ, CO.

Fractional distillation of crude oil

Heat crude oil; vapour rises up a column; fractions condense at different heights based on boiling point.

Process.

Crude oil heated in a furnace ( $\sim 350\degree\text{C}$ ) → vaporises.
Vapour enters a fractionating column with temperature gradient (HOT at bottom, COOL at top).
As vapour rises, different molecular sizes condense at different heights:
- SHORT-chain molecules (low b.p.) rise highest before condensing.
- LONG-chain molecules (high b.p.) condense low.
Each fraction collected at a different level.

Fractions, top to bottom (small to large molecule, low to high b.p.).

Fraction	Carbons	Use
Refinery gas	C₁-C₄	Bottled gas (LPG), home cooking
Gasoline (petrol)	C₅-C₁₀	Car fuel
Naphtha	C₆-C₁₀	Petrochemical feedstock (plastics, etc.)
Kerosene (paraffin)	C₁₀-C₁₆	Aircraft fuel, heating
Diesel	C₁₄-C₂₀	Road vehicles, trains
Fuel oil	C₂₀-C₃₀	Power stations, ships
Bitumen	C₃₀+	Roads, roofing

Properties going DOWN the column.

Boiling point INCREASES.
Viscosity (thickness) INCREASES.
Volatility (ease of evaporation) DECREASES.
Flammability DECREASES.
Colour darkens.

Why? Larger molecules = stronger intermolecular forces (more contact area) = harder to vaporise = higher b.p.

The column is hot at the bottom, cool at the top — small, low-boiling fractions leave high up; large, high-boiling fractions leave low down.

Cracking. Long-chain hydrocarbons are LESS USEFUL than short-chain. Cracking breaks long molecules into short, more useful ones (esp. alkenes for plastics): $\text{C}_{12}\text{H}_{26} \to \text{C}_{8}\text{H}_{18} + \text{C}_{4}\text{H}_{8} \text{ (an alkene)}.$

Done at high T with a catalyst (e.g. Al₂O₃).

Crude oil = mixture of hydrocarbons.
Fractional distillation: T gradient in column.
Top: small molecules, low b.p. Bottom: large, high b.p.
Fractions: refinery gas, gasoline, naphtha, kerosene, diesel, fuel oil, bitumen.
Cracking: break long → short chains.

Combustion of fuels

Complete: HC + O₂ → CO₂ + H₂O. Incomplete: CO and/or C.

Complete combustion (plenty of oxygen). $\text{hydrocarbon} + \text{O}_{2} \to \text{CO}_{2} + \text{H}_{2}\text{O}.$

Worked. Methane: $\text{CH}_{4} + 2\text{O}_{2} \to \text{CO}_{2} + 2\text{H}_{2}\text{O}$ . Worked. Octane: $2\text{C}_{8}\text{H}_{18} + 25\text{O}_{2} \to 16\text{CO}_{2} + 18\text{H}_{2}\text{O}$ .

Strategy for balancing: balance C, then H, then O.

Incomplete combustion (insufficient oxygen).

Produces CO (carbon monoxide) and/or C (soot/carbon).
$2\text{CH}_{4} + 3\text{O}_{2} \to 2\text{CO} + 4\text{H}_{2}\text{O}$ .
$\text{CH}_{4} + \text{O}_{2} \to \text{C} + 2\text{H}_{2}\text{O}$ .

Why bad?

CO: poisonous (binds haemoglobin).
Soot: particulates → respiratory issues, blackens surfaces.
Less heat released per mole of fuel (incomplete reaction).

More oxygen gives complete combustion (CO₂ + H₂O); too little oxygen gives toxic CO and soot.

Cambridge tip. When given a combustion question, ALWAYS write the balanced equation. Check C, H, O atom counts on both sides.

Worked qualitative. A faulty gas heater produces CO. What's the cause? Insufficient air supply, poor ventilation, or a blocked vent. Fix: ensure good ventilation; service the heater regularly. CO detectors save lives in homes with gas appliances.

Complete: HC + O₂ → CO₂ + H₂O.
Incomplete: CO and/or C produced.
Less heat from incomplete combustion.
Balance: C, H, O in that order.

Alternative fuels — hydrogen, biofuels

Hydrogen: only water as product. Biofuels: renewable, but not zero-impact.

Hydrogen.

Combustion: $2\text{H}_{2} + \text{O}_{2} \to 2\text{H}_{2}\text{O}$ . Only product: water.
Excellent fuel by mass: huge energy density per kg.
Used in fuel cells (see study note) and rockets.
Drawbacks: storage (H₂ leaks easily, must be high-pressure or liquid); production (most H₂ today comes from natural gas, releasing CO₂; "green" H₂ from electrolysis with renewable electricity).

Biofuels.

Bioethanol: from fermentation of sugar/starch crops (sugar cane, corn, wheat).
- $\text{C}_{6}\text{H}_{12}\text{O}_{6} \to 2\text{C}_{2}\text{H}_{5}\text{OH} + 2\text{CO}_{2}$ (yeast fermentation).
Biodiesel: from vegetable oils.
Biogas (methane): from anaerobic decomposition of waste.
Renewable: crops can be regrown.
BUT: needs large land area (food vs fuel debate); can release CO₂ in production / processing; not zero-impact.

Carbon-neutral? In theory, biofuels are CARBON NEUTRAL: the CO₂ released by burning equals the CO₂ absorbed by the crops as they grew. In practice, fertiliser production, farm machinery and transport contribute CO₂ → not quite zero-net.

Worked qualitative. Why is hydrogen often called a "clean fuel"? Combustion produces only water — no CO₂, CO, SO₂, NOₓ, or particulates. The catch: H₂ production may not be clean unless renewable electricity is used.

Hydrogen: combustion only makes water.
Biofuels: bioethanol, biodiesel, biogas.
Bioethanol: yeast fermentation of sugars.
Carbon-neutral idea — not perfect in practice.

How it’s examined

Fuels appear every Paper 4 (8-10 marks): fractional distillation diagram, name fractions, balance combustion equations, distinguish complete vs incomplete. Examiner reports flag students confusing the order of fractions in the column (top is small/light, bottom is heavy/large).

Sources: Cambridge IGCSE Chemistry 0620 syllabus 2026-2028 (13.2); 0620/42 Oct/Nov 2024 — Q21 (fractional distillation); 0620 Examiner Reports 2022-2024. Last reviewed 2026-05-07.

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Step-by-step worked examples — Fuels

Step-by-step solutions to past-paper-style questions on fuels, written exactly the way a tutor would explain them at the board.

1Fractions of crude oil
Core• fractions
Question
Name four major fractions of crude oil and one use of each.
Step-by-step solution
1. Step 1
  Refinery gas → gas cookers/heating.
2. Step 2
  Gasoline (petrol) → cars.
3. Step 3
  Kerosene (paraffin) → aircraft fuel.
4. Step 4
  Diesel oil → trucks and lorries.
5. Step 5
  Bitumen (residue) → road surfaces, roofing.
Answer
Refinery gas (heating); petrol (cars); kerosene (aircraft); diesel (trucks); bitumen (roads).
2Complete combustion of methane
Core• Adapted from 0620/22 May/Jun 2024 Q15• combustion
Question
Write the equation for the complete combustion of methane.
Step-by-step solution
1. Step 1
  Hydrocarbon + plenty of O₂ → CO₂ + H₂O.
  $\text{CH}_{4} + 2\text{O}_{2} \to \text{CO}_{2} + 2\text{H}_{2}\text{O}$
Answer
$\text{CH}_{4} + 2\text{O}_{2} \to \text{CO}_{2} + 2\text{H}_{2}\text{O}$
3Incomplete combustion
Extended• incomplete
Question
Write a possible equation for the incomplete combustion of methane.
Step-by-step solution
1. Step 1
  Limited oxygen → produces CO and/or C (soot).
  $2\text{CH}_{4} + 3\text{O}_{2} \to 2\text{CO} + 4\text{H}_{2}\text{O}$
Answer
$2\text{CH}_{4} + 3\text{O}_{2} \to 2\text{CO} + 4\text{H}_{2}\text{O}$ (or CO + C, depending on O₂ supply).
Examiner tip
Mark schemes accept any reasonable equation showing CO or C as the carbon product.
4Fractional distillation principle
Extended• distillation
Question
Explain how fractional distillation separates the components of crude oil.
Step-by-step solution
1. Step 1
  Heat crude oil → vapours rise up a tower with a temperature GRADIENT (hottest at bottom).
2. Step 2
  Each fraction condenses at a different height when its boiling-range temperature is reached.
3. Step 3
  Smaller molecules → lower boiling points → condense HIGHER up.
Answer
Vapours rise; each fraction condenses at a height matching its boiling-point range.

Key Formulae — Fuels

The formulae you need to memorise for fuels on the Cambridge IGCSE 0620 paper, with every variable defined in plain English and a note on when to use it.

Combustion of hydrocarbons
$\text{Complete: CO}_{2} + \text{H}_{2}\text{O};\ \text{Incomplete: CO + H}_{2}\text{O (or C + H}_{2}\text{O)}$
When to use
Combustion equations.

Key Definitions and Keywords — Fuels

Definitions to memorise and the exact keywords mark schemes credit for fuels answers — sharpened from recent examiner reports for the 2026 0620 sitting.

Fossil fuel
Examiner keyword
A fuel formed from the remains of ancient organisms (coal, crude oil, natural gas).
Hydrocarbon
Examiner keyword
Compound containing ONLY hydrogen and carbon atoms.
Fractional distillation
Examiner keyword
Separation method exploiting different boiling points to separate the fractions of crude oil.
Complete combustion
Examiner keyword
Burning in PLENTY of oxygen → CO₂ + H₂O.
Incomplete combustion
Examiner keyword
Burning in LIMITED oxygen → CO and/or soot (C) + H₂O.

Common Mistakes and Misconceptions — Fuels

The traps other students keep falling into on fuels questions — taken from recent Cambridge IGCSE 0620 examiner reports and mark schemes — and how to avoid them.

✕Putting bitumen at the top of the tower
0620/42 — recurring
Why it happens
Inverting the gradient.
How to avoid it
BITUMEN (heavy, high b.p.) at the BOTTOM. Refinery gas (light, low b.p.) at the TOP.
✕Producing only CO₂ in incomplete combustion
Why it happens
Defaulting to complete.
How to avoid it
Incomplete: CO and/or C (soot) — NOT CO₂.
✕Failing to balance combustion equations
Why it happens
Forgetting H atoms.
How to avoid it
Balance C, then H, then O. The O₂ coefficient may need to be a fraction.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

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Video lesson

Short walkthrough of the concepts students most often get stuck on.

Fuels — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Fraction

Carbons

Use

Refinery gas

C₁-C₄

Bottled gas (LPG), home cooking

Gasoline (petrol)

C₅-C₁₀

Car fuel

Naphtha

C₆-C₁₀

Petrochemical feedstock (plastics, etc.)

Kerosene (paraffin)

C₁₀-C₁₆

Aircraft fuel, heating

Diesel

C₁₄-C₂₀

Road vehicles, trains

Fuel oil

C₂₀-C₃₀

Power stations, ships

Bitumen

C₃₀+

Roads, roofing

Complete combustion (plenty of oxygen). $\text{hydrocarbon} + \text{O}_{2} \to \text{CO}_{2} + \text{H}_{2}\text{O}.$

Strategy for balancing: balance C, then H, then O.

Incomplete combustion (insufficient oxygen).

Produces CO (carbon monoxide) and/or C (soot/carbon).
$2\text{CH}_{4} + 3\text{O}_{2} \to 2\text{CO} + 4\text{H}_{2}\text{O}$ .
$\text{CH}_{4} + \text{O}_{2} \to \text{C} + 2\text{H}_{2}\text{O}$ .

Why bad?

CO: poisonous (binds haemoglobin).
Soot: particulates → respiratory issues, blackens surfaces.
Less heat released per mole of fuel (incomplete reaction).

More oxygen gives complete combustion (CO₂ + H₂O); too little oxygen gives toxic CO and soot.

Cambridge tip. When given a combustion question, ALWAYS write the balanced equation. Check C, H, O atom counts on both sides.

Fuels

Short Study Notes in the form of Slides

Short Study Notes — Fuels

Detailed Notes

What you’ll learn

How it’s examined

1Fractions of crude oil

2Complete combustion of methane

3Incomplete combustion

4Fractional distillation principle

Combustion of hydrocarbons

Fossil fuel

Hydrocarbon

Fractional distillation

Complete combustion

Incomplete combustion

✕Putting bitumen at the top of the tower

✕Producing only CO₂ in incomplete combustion

✕Failing to balance combustion equations

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Fuels — frequently asked questions

Fuels

Short Study Notes in the form of Slides

Short Study Notes — Fuels

Detailed Notes

What you’ll learn

How it’s examined

1Fractions of crude oil

2Complete combustion of methane

3Incomplete combustion

4Fractional distillation principle

Combustion of hydrocarbons

Fossil fuel

Hydrocarbon

Fractional distillation

Complete combustion

Incomplete combustion

✕Putting bitumen at the top of the tower

✕Producing only CO₂ in incomplete combustion

✕Failing to balance combustion equations

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Fuels — frequently asked questions