Chemistry

1. Incomplete Combustion
Summary based on Save My Exams
resource

2. What is Incomplete Combustion?
• - Happens with limited oxygen supply
• - Produces water and either carbon monoxide
or carbon (soot)
• - Occurs in car engines, faulty boilers
• - Yellow flame in Bunsen burner (vs blue for
complete combustion)

3. Carbon Monoxide from Incomplete
Combustion
• - Produced when there's reduced oxygen
• - Word equation: Fuel + oxygen → carbon
monoxide + water
• - Example: C₃H₈ + 3½O₂ → 3CO + 4H₂O
• - CO is colorless, odorless, toxic
• - Binds irreversibly to hemoglobin, limiting
oxygen transport

4. Carbon (Soot) from Incomplete
Combustion
• - Very limited oxygen leads to carbon (soot)
formation
• - Sooty, yellow flame is a key indicator
• - Hydrocarbons with high carbon % produce
more soot
• - Used to distinguish organic compounds

5. Worked Example – Carbon
Composition
• - % Carbon = (Mass of Carbon / Molar Mass) ×
100
• - Cyclohexane (C₆H₁₂): 86%
• - Nitrobenzene (C₆H₅NO₂): 59%
• - Naphthalene (C₁₀H₈): 94%

6. Observing Combustion Sootiness
• - Naphthalene: Most sooty flame (highest C%)
• - Nitrobenzene: Least sooty flame (lowest C%)

7. Final Notes
• - Incomplete combustion never produces
hydrogen
• - Hydrogen is preferentially oxidised over
carbon