Revision: Organic Chemistry >> Hydrocarbons : Alkanes Chemistry (English Medium) ICSE Class 10 CISCE

Alkanes are hydrocarbons in which all the linkages between the carbon atoms are single covalent bonds.

• Source: Methane forms in marshes, coal mines, and during cellulose fermentation.
• Greenhouse Gas: It traps 20× more heat than CO₂ and stays in the atmosphere for ~10 years.
• Uses & Emission: Comes from landfills, farming, fossil fuels, and can be used as clean energy.

• Physical State: Methane and ethane are colourless, odourless gases.
• Boiling & Melting Points: Methane (b.p. -162 °C, m.p. -183 °C), Ethane (b.p. -89 °C, m.p. -172 °C).
• Solubility: Both are insoluble in water but dissolve well in organic solvents.

• Complete Combustion: Alkanes burn in air to give CO₂ and H₂O with a bluish, non-sooty flame.
• Incomplete Combustion: In limited air, alkanes form CO or soot (C) along with water.
• Substitution Reaction: In the presence of sunlight, alkanes react with halogens (Cl₂, Br₂, I₂) to form alkyl halides.
• Catalytic Oxidation: Alkanes form alcohols, aldehydes, or acids using catalysts like Cu, MoO₃, or Pt under specific conditions.
• Slow Oxidation: With oxidising agents (e.g., K₂Cr₂O₇), alkanes oxidise stepwise to alcohols, aldehydes, acids, and finally CO₂ + H₂O.

• Methane is a source of carbon monoxide and hydrogen and is also used as a domestic fuel.
• Methane helps in the preparation of compounds like ethyne, methanol, chloromethane, and carbon tetrachloride.
• Halothane (CF₃CHBrCl) has replaced chloroform for anaesthetic use due to its safer properties.
• Ethane is used to produce ethene, ethanol, acetaldehyde, and acetic acid.
• Ethane is used to form ethyl chloride (for tetraethyllead) and acts as a fuel and dry-cleaning solvent.