Chemistry Topic 7 - Organic Chemistry


Organic Chemistry:

Crude Oil, hydrocarbons and alkanes:

Fractional Distillation of crude oil:

  • Crude oil is a mixture of hydrocarbons: compounds that contain only C and H atoms.
  • Crude oil is separated into fractions by fractional distillation.
  • The longest molecules have the strongest intermolecular forces, so they have the highest boiling point and condense nearer the bottom of the fractionating column.
  • The fractions of crude oil are called: LPQ, Petrol, Kerosene, Diesel, Heavy Fuel Oil and Bitumen.
  • Properties of Small molecules are: Low boiling point, Very volatile, flows easily and Ignites easily.
  • Properties of Large molecules are: High boiling point, not very volatile, does not flow easily and does not ignite easily.


  • Alkanes are a homologous series of hydrocarbons.
  • Alkanes haven the general formula CnH2n+2
  • The first four alkanes are methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10).
  • The alkanes are saturated hydrocarbons because all the carbon atoms are joined by C-C single bonds.


  • Cracking is a reaction which breaks long, less useful hydrocarbons into shorter, more useful hydrocarbons.
  • Cracking helps to match supply and demand for the different fractions.
  • A long alkane is broken into a shorter alkane (for fuels) and a shorter alkene (a chemical feedstock).


  • Alkenes are a homologous series of hydrocarbons. Alkenes have the general formula CnH2n.
  • The


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