Organic Chemistry

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Alkanes

Alkanes are Hydrocarbons

  • Hydrocarbons are molecules made up of hydrogen and carbon atoms only 
  • Different alkanes have different chain lengths
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Alkanes

Alkanes are part of a Homologous Series

  • A Homologous series is a group of compounds that can all be represnted by the same general formula
  • Alkanes all have the general formula CnH2n+2
  • No more atoms can join onto the carbon atoms so they are saturated.

Complete Combustion

  • Complete combustion releases lots of energy and only produces 2 waste products
  • alkane + oxygen > carbon dioxide + water (+ energy)
  • CH3 + 2O2 > CO2 + 2H2O

Incomplete Combustion

  • When there is a limited supply of oxygen, carbon monoxide is produced
  • alkane + oxygen > carbon monoxide + carbon dioxide + water
  • 4CH4 + 6CO2 > C + 2CO + CO2 + 8H2O
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Alkanes with Halogens

HaloAlkanes

  • Chlorine and Bromine react with alkanes in the prescence of UV light
  • In these reactions, a hydrogen atom from the alkane is substituted (replaced) by chlorine or bromine.
  • This is called a substitution reaction
  • This is how bromine and methane react together to from bromomethane

methane + bromine > bromomethane + hydrogen bromide 

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Alkenes

C=C Double Bond

  • Alkenes are hydrocarbons with a double bond between 2 of the carbon atoms in their chain 
  • They are unsaturated because they can make more bonds, the doube bond can open up, allowing the carbon atoms to bond with other atoms.
  • All alkenes have the general formula CnH2n

 

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Alkenes

HaloAlkenes

  • Halogens react with alkenes to form haloalkenes
  • For example, bromine and ethene react together to form dibromoethane
  • ethene + bromine > dibromoethane
  • These are called addition reactions because the C=C double bond is split and a halogen atom is added to each of the carbon atoms

Alkenes Turn Bromine Water Colourless

  • This is often used as a test for C=C double bonds
  • bromine water + alkene > SHAKE > colourless solution
  • orange > colourless 
  • It changes because the orange bromine molecules react with alkene to make dibromoalkane
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Ethanol

Ethanol can be produced from Ethene and Steam

  • The reaction needs 300 degrees celsius and a pressure of 60-70 atmospheres.
  • Phosphoric acid is used as a catalyst
  • C2H4 + H2O > C2H5OH
  • This is a cheap process , but crude oil is non renewable so it will become expensive

Fermentation

  • The raw material used for fermentation is sugar. This is converted into ethanol using yeast
  • 30 degrees celsius is needed and simpler equipment than when using ethene
  • This process uses renewable resources 
  • The ethanol produced is not very concentrated so it needs to be distilled and purified.
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