GCSE C3 Chapter 5

Structures of alcohols, carboxylic acids and ester

  • Organic molecules form the basis of living things and all contain carbon atoms
  • Bond covalently to form the "backbone" of many series of organic molecules
  • Series of molecules which have a general formula are called homologous series
  • Alcohols - Functional group -O-H - 



  • Carboxylic acids - Functional group COOH



  • Esters - Functional group COO
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Properties and uses of alcohols

  • Alcohols with small molecules (methanol,ethanol,propanol) mix well with water and produce neutral solutions
  • Many organic substances dissolve in alcohols making them useful solvents
  • Ethanol is the main ingredient in beer, wine and other alcoholic drinks
  • Alcohols burn in air to produce carbon dioxide and water
  • Used as fuels - spirit burners, combustion engines, mixed with petrol
  • Ethanol   + Oxygen  = Carbon dioxide +  water
  • C2H5OH +    3O2     =       2CO2           3H2O
  • They react with sodium to produce hydrogen gas and form a solution - reaction less vigorous than sodium with water
  • Alcohols can be oxidised by chemical oxidising agents such as potassium dichromate to produce carboxylic acids
  • Some microbes in the air can also oxidise solutions of ethanol to produce ethanoic acid which turns drinks sour and is the main ingredient in vinegar
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Carboxylic acids

  • Carboxylic acids dissolve in water to produce solutions with a pH of less than 7
  • Properties typical of all acids
  • Carboxylic acids + carbonates = salt + carbon dioxide + water
  • React with alcohols to produce esters
  • Ethanol + ethanoic acid = ethyl ethanoate + water (Sulphuric acid catalyst)
  • Carboxylic acids are described as being weak acids:
    • When strong acids dissolve in water to produce solutions they ionise compltely - the compound is broken down completley to produce H+ ions
    • HCl(aq) = H+(aq) + Cl-(aq)
    • When carboxylic acids dissolve in water the acid is not broken down completley, part of the comound remains
    • CH3COOH(aq) = CH3COO-(aq) + H+(aq)

  • Weak acids do not ionise completely in aqueous solutions
  • Acids of the same volume - strong acids have a lower pH and react quicker
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Organic issues

  • All important organic chemicals that can be used in many ways: fuels, foods, drinks, solvents
  • Advantages:
    • Can be used as fuels to save limited resources
    • Less polluting, carbon neutral
  • Disadvantages:
    • Can be abused leading to health and social issues
    • Farmland used to grow crops used for production of fuels could be used for food
  • Advantages and disadvantages for use of resources may change over time or when their are new developments and so monitoring and careful research is needed
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