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CBSESecondary School (English Medium) (5 to 8) Class 8
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Chemical Properties of Carbon Compounds > Combustion

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  • Key Points: Combustion
Maharashtra State Board: Class 10

Combustion

Combustion is the process of burning carbon compounds in the presence of oxygen, producing carbon dioxide, water vapour, heat, and light.

1. C + O₂ → CO₂ + heat + light 

   (Carbon)

2. CH₄ + 2O₂ → CO₂ + 2H₂O + heat + light

  (Methane)

3. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + heat + light 

  (Ethanol)

Observations:

  • Saturated hydrocarbons burn with a clean blue flame (complete combustion).
  • Unsaturated hydrocarbons burn with a yellow, sooty flame due to excess carbon and incomplete combustion.
  • Incomplete combustion produces carbon monoxide (CO), a poisonous gas that binds with haemoglobin to form carboxyhaemoglobin, reducing oxygen supply to body tissues and potentially causing death.
Maharashtra State Board: Class 10

Experiment 1

1. Aim: To observe the flame characteristics during the combustion of saturated and unsaturated carbon compounds and detect soot formation.

2. Requirements: Bunsen burner, copper gauze, metal plate, ethanol (saturated compound), acetic acid, and naphthalene (unsaturated compound).

3. Procedure

  1. Place 3–4 drops (or a pinch) of one compound (e.g., ethanol) on clean copper gauze.
  2. Hold the gauze in the blue flame of a Bunsen burner.
  3. Observe whether the flame is blue or yellow and whether smoke or soot is formed.
  4. Hold a metal plate above the flame and check for black soot deposits.
  5. Repeat the same with acetic acid and naphthalene.
  6. Adjust the air hole of the burner to observe changes in flame colour.

4. Observations

  • Ethanol burns with a clean blue flame (complete combustion, no soot).
  • Naphthalene burns with a yellow sooty flame (incomplete combustion, black soot forms).
  • Limited oxygen supply (closed air hole) gives a yellow sooty flame, even with ethanol.
  • An open air hole gives a blue flame with the proper oxygen mix.

5. Conclusion

  • Saturated compounds (like ethanol) burn cleanly with a blue flame.
  • Unsaturated compounds (like naphthalene) burn with a yellow flame and produce soot due to higher carbon content.
  • The flame colour and soot formation indicate the degree of saturation and availability of oxygen.
CBSE: Class 10
Maharashtra State Board: Class 10

Key Points: Combustion

  • Carbon compounds combust in oxygen to produce carbon dioxide, water (for hydrocarbons), heat, and light.
  • Hydrocarbons such as methane, ethanol, and propane undergo complete combustion, releasing energy.
  • Complete combustion is indicated by a clean, blue flame, while incomplete combustion produces a yellow, sooty flame.
  • Combustion is an important chemical property of carbon compounds, especially common fuels.
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