C7 specification

• describe what crude oil is & where it comes from

  • fossil fuel found in rocks
  • remains of plankton buried in mud millions of years ago
  • made of a mixture of lots of hydrocarbons called alkanes
• describe the general chemical formula for the alkanes 

  Cn H2n+2
• state the names of the first four members of the alkanes

  • methane
  • ethane
  • propane
  • butane
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• recognise substances as alkanes from their formulae

  • methane = CH4
  • ethane = C2H6
  • propane = C3H8
  • butane = C4H10
• Describe the process of fractional distillation

  1. oil heated until most turns into gas
  2. gas enters fractional column
  3. longer hydrocarbons have higher boiling points so condense into liquid early on
  4. shorter hydrocarbons have lower boiling points & condense where it's cooler
  5. oil mixture is separated into different fractions based on carbon atoms
• state the names and uses of fuels that are produced from crude oil by fractional distillation

  • oil provides fuel for most modern transport
  • petrochemical industry uses it to make lubricants
• Describe hydrocarbons

  • made up oh hydrogen & carbon only
• Describe trends in the properties of hydrocarbons

  • shorter carbon chains are less viscous (gloopy)
  • shorter = more volatile (lower boiling points)
  • shorter= more flammable
• explain how their properties influence how they are used as fuels

  • properties of hydrocarbons affect how they're use for fuels
• complete combustion

  • releases lots of energy
  • only waste products are carbon dioxide & water vapour
• complete combustion

  hydrogen + carbon → carbon dioxide + water
• complete combustion

  • during combustion, both carbon & hydrogen are oxidised
  • hydrocarbons used as fuels due to the amount of energy released when they combust completely
• cracking means splitting up long-chain hydrocarbons
• • all products from crude oil are organic compounds (contains carbon atoms)
  • large variety of products is because carbon atoms can bond to form different homologous series
  • alkanes & alkenes are examples of a homologous series
  • contains similar compounds
• test for alkenes

  • use BROMINE WATER

  1. when bromine is added to an alkane, no reaction will happen
  2. if added with alkene, bromine reacts to become colourless; bromine is decolourised

  A) alkane

  B) alkene

  C) decolourised

  
• cracking

  • long alkane molecules from fractional distillation are turned into smaller, more useful ones through CRACKING
  • cracking produced alkenes
  • more reactive
  • used as a starting material when making other compounds
• describe the process of cracking

  • cracking is a thermal decomposition reaction- breaking molecules down by heating them

  1. heat long chain hydrocarbons to vaporise them
  2. vapour is passed over a hot powdered aluminium oxide catalyst
  3. long chain molecules split apart on surface of catalyst - this is catalystic cracking

  • you can also crack hydrocarbon if you vaporise them, mix with steam & heat to a very high temperature- this is steam cracking
• • alkenes have double carbon bonds
• Explain why cracking is useful and why modern life depends on the uses of hydrocarbons

  • converts larger hydrocarbons into smaller, more useful ones
  • produces alkenes which is used for starting material for other compounds
  • useful for petrochemical industry
• why are hydrocarbons used as fuels

  due to amount of energy released when they combust completely
• what are the waste products of complete combustion

  carbon dioxide & water vapour
• where do shorter hydrocarbons condense in fractional distillation

  where it's cooler
• how are hydrocarbons fractioned

  based on number of carbon atoms