alcohols

• Alcohols


  Organic compounds containing the hydroxyl (-OH) functional group
• General formula of alcohols

  CnH2n+1OH, where n is the number of carbon atoms
• Their names end with 'anol'
• Colourless and neutral liquids
• Alcohols contain the -OH group but they are not alkalis, they are neutral
• Alcohols

  • Methanol (CH3OH)
  • Ethanol (C2H5OH)
  • Propanol (C3H7OH)
  • Butanol (C4H9OH)
• The relative molecular mass of each alcohol increases from the previous one by 14, due to the addition of a -CH2 unit
• 
  

  • Have low boiling points
  • Require little energy to overcome the weak intermolecular forces of attraction holding the molecules together
• Soluble in water
• Combustion of alcohols


  Alcohols burn completely in air to form carbon dioxide and water vapour
• Oxidation of alcohols


  Alcohols can be oxidised by atmospheric oxygen or oxidising agents to form carboxylic acids
• Oxidation of ethanol


  • Ethanol (C2H5OH) can be oxidised to form ethanoic acid (CH3COOH)
• Oxidation of alcohols by atmospheric oxygen

  Ethanol + oxygen -> Ethanoic acid + water
• This is the reason why alcoholic drinks turn sour when exposed to air - the bacteria in air oxidises ethanol in wine/beer to ethanoic acid, using the oxygen from the air
• Oxidation of alcohols by oxidising agents

  Ethanol + oxidising agent (acidified KMnO4) -> Ethanoic acid + water
• Oxidising agent


  Acidified potassium manganate (VII), KMnO4
• Condition for oxidation by oxidising agents

  Heat under reflux (continuous boiling)
• The colour of the potassium manganate (VII) changes from purple to colourless during the oxidation reaction
• Fermentation of glucose to produce ethanol

  Glucose (C6H12O6) -> 2 Ethanol (C2H5OH) + 2 Carbon dioxide (CO2)
• Fermentation


  • Requires yeast, temperature of 37 degrees Celsius, and absence of oxygen
• Yeast


  Living cells containing enzymes that help convert sugar into ethanol
• The enzymes in yeast work best at 37 degrees Celsius, and are denatured by heat above this temperature
• The absence of oxygen ensures the ethanol formed is not oxidised to ethanoic acid
• Fermentation of wine


  • Using a demijohn flask
  • Industrial fermentation of wine
• The industrial preparation of ethanol involves the catalysed addition of steam to ethene at 300 degrees Celsius and 60 atm pressure, using phosphoric (V) acid as the catalyst
• Relative molecular mass of alcohols


  The relative molecular mass of each alcohol increases from the previous one by 14, due to the addition of a -CH2 unit
• Heat under reflux


  A laboratory technique where a reaction mixture is heated while being constantly refluxed, which allows the reaction to occur at an elevated temperature without the loss of volatile components
• Stirring


  The process of mixing a reaction mixture to ensure that all components are evenly distributed and have an equal opportunity to react