c9 crude oil and fuels

• crude oil is a mixture of hundreds of different hydrocarbons
• hydrocarbons are compounds made up of only hydrogen and carbon atoms
• most hydrocarbons are alkanes
• alkanes are saturated hydrocarbons because they only have single carbon-carbon bonds
• as the hydrocarbon chain length increases

  • more intermolecular foces
  • more energy needed to break them
  • molecules are larger
  • melting and boiling point increase
• viscosity


  how thick something is
• volatility


  ability to become a vapour
• general structure for alkanes 


  CnH2n+2
• increasing number of carbons in hydrocarbon chains

  • increases melting and boiling point
  • increase volatility
  • decrease viscosity
  • decrease flammability
• more carbons in hydrocarbons means a longer chain
• less carbons in hydrocarbons means a shorter chain
• soot is produced due to excess carbon in incomplete combustion
• carbon dioxide

  • CAUSE: complete combustion of fossil fuels
  • EFFECT: contribute to global warming
• carbon monoxide

  • CAUSE: incomplete combustion
  • EFFECT: toxic gas (death)
• sulphur dioxide

  • CAUSE: oxidation of sulphur impurities in fossil fuels
  • EFFECT: acid rain
• nitrogen oxide

  • CAUSE: oxidation of nitrogen gas in the air at high temperatures (vehicle engines)
  • EFFECT: acid rain, triggers asthma
• particules

  • CAUSE: incomplete combustion of diesel
  • EFFECT: global dimming
• pollutants

  • carbon dioxide
  • carbon monoxide
  • sulphur dioxide
  • nitrogen oxide
  • particules
• complete combustion


  fuel is fully oxidised
• the products of complete combustion of a hydrocarbon are alays carbon dioxide and water
• incomplete combustion


  a fuel is not fully oxidised
• carbon monoxide


  colourless odourless tasteless toxic gas
• the products of incomplete combustion of a hydrocarbon are carbon monoxide and water
• carbon monoxide binds with the iron in haemoglobin in red blood cells meaning less oxygen can get to body cells
• fractional distillation


  separates miscible liquids of different boiling points
• fractional distillation of crude oil

  1. crude oil is boiled and fed into the column
  2. the longest chain condense at the bottom where it is hottest
  3. the shorter chains condense further up the column depending on their boiling point
  4. the shortest chains which are gases at room temperature are tapped off at the top where it is coolest
  5. the different fractions are tapped off and go on to further distillation to make the fractions pure
• cracking 


  when large hydrocarbon molecules are broken down into smaller hydrocarbons using heat and a catalyst (thermal decomposition)
• cracking hydrocarbons

  1. long chain fractions are heated and vaporised
  2. vapours pass over a nickel catalysts (or reacted with steam)
  3. products are short chain hydrocarbons (a mixture of alkanes and alkenes)
• why are long chain hydrocarbons cracked

  • low supply of short chain hydrocarbons
  • high demand for short chain hydrocarbons
  • high supply long chain hydrocarbons
  • low demands for long chain hydrocarbons
• cracking long chain hydrocarbons produces useful short chain hydrocarbons which can be used to make plastics or burnt as fuel
• alkenes are a family of hydrocarbon compounds with the general formula CnH2n
• alkenes contain double covalent bonds between carbon atoms
• alkenes are unsaturated hydrocarbons
• we can test for unsaturated hydrocarbons using bromine water which turns colourless in the presence of an alkene