Organic Chemistry

• crude oil is a finite resource found in rocks
• crude oil comes from plankton
• crude oil is a mixture of a very large number of compounds
• most compounds in crude oil are hydrocarbons
• hydrocarbons are molecules made up of only hydrogen and carbon atoms
• most hydrogens in crude oil are alkanes
• formula for alkanes: CnH2n+2
• alkanes are a group of hydrocarbons
• the first 4 alkanes are methane, ethane, propane and butane
• alkane molecules can be represented as C2H6
• hydrocarbons in crude oil can be separated into fractions
• each fraction of hydrocarbons contains molecules with a similar number of carbon atoms
• fractions can be used to produce fuels or feedstock
• fuels that we depend on include, petrol, diesel, oil, kerosene
• useful materials produced by the petrochemical industry include:

  • solvents,
  • lubricants
  • polymers
  • detergents
• fractional distillation for crude oil practical:

  • oil is heated until most of it turns into a gas
  • these gases enter fractional columns
  • longer chains of hydrocarbons have high boiling points
  • shorter chains of hydrocarbons have lower boiling points
  • the crude oil is now separated out into different fractions
  • longer chains of hydrocarbons condense into liquids early on
  • shorter chains of hydrocarbons condense into liquids later on
• a hydrocarbons properties depend on the length of the hydrocarbon
• the shorter the chain of hydrocarbons, the more runny the hydrocarbon is, so it is less viscous
• shorter hydrocarbons are more volatile so it is easily evapourated
• shorter hydrocarbons are more flammable
• the combustion of hydrocarbons releases energy
• during the combustion of hydrocarbons, the carbon and hydrogen atoms are oxidised
• the oxidation of hydrocarbons:

  hydrocarbon + oxygen  → carbon dioxide + water
• cracking is when long chains of hydrocarbons are broken down to produce smaller and more useful chains
• methods of cracking:

  • catalytic cracking
  • steam cracking
• the products of cracking are alkanes and alkenes
• alkenes are more reactive than alkanes
• to test for alkenes you add bromine water and heat the mixture
• bromine water test for alkenes:

  • when orange bromine water is added to alkanes, no reaction happens and the solution stays orange
  • when orange bromine water is added to alkenes, a colourless compound is formed
• cracking is useful because there is a high demand for fuels with small molecules
• alkenes are produced because they produce polymers