Organic Chemistry

• What is crude oil?

  A finite resource.

  A mixture of compounds; containing of the remains of ancient biomass.
• What is a hydrocarbon?

  A compound made up exclusively of hydrogen and carbon atoms.

  
• What are alkanes?

  Saturated Hydrocarbons; Formula CnH2n
• What is homologous series?

  Series of compounds with the same general formula, same functional group and similar chemical properties.
• Describe the combustion of hydrocarbons:

  • Exothermic reaction occurring when hydrocarbons are reacted with oxygen
  • Complete combustion produces carbon dioxide and water (carbon atoms are fully oxidised to form CO₂ and Hydrogen Atoms are fully oxidised to form H₂O)
  • Incomplete combustion produces carbon, carbon monoxide and water.

  
• Describe the physical properties of alkanes:

  • First few in series are gases at room temperature, then change to liquid as hydrocarbon chains increase in size, then solid
  • In general, boiling points and viscosity increase as molecules get larger
  • Volatility and flammability decrease as molecules get larger
  • Poor reactivity
• Describe how fractional distillation of crude oil takes place:

  • Crude Oil is heated and vaporised
  • Vapor rises up the fractionating column (tower)
  • The column is hotter on the bottom and cooler at the top
  • Hydrocarbons cool as they travel up the fractionating column and condense at different heights as they have different boiling points
  • Large molecules, high boiling points - collected at the bottom
  • Small molecules, low boiling points - collected at the top
  • This gives fractions which have several uses (see image)

  
• What is cracking?

  When large hydrocarbons are thermally broken down into smaller and more useful molecules.
• What type of reaction is cracking?

  Thermal decomposition

  
• What are the conditions for cracking?

  Reactant heated to vapour, passed over a hot catalyst (catalytic cracking) or heated to vapour, mixed with steam and heated to high temperatures (steam cracking)
• How are the products of cracking used?

  The products are alkanes and alkenes - alkenes used to make polymers and plastics.
• What is an alkene?

  Unsaturated hydrocarbon, contains a C=C bond

  General formula for alkenes is CnH2n
• What is the test for alkenes?

  Add bromine water. Colour changes from orange to colourless.
• Describe the combustion of alkenes.

  They burn with smoky flames due to incomplete combustion.