Oxidation of Ethanol (Edexcel IGCSE Chemistry)

• Ethanol can undergo oxidation in three different ways:
  • Combustion
  • Aerobic oxidation
  • Treatment with an oxidising agent

Combustion

• Alcohols undergo combustion to form carbon dioxide and water
• The complete combustion of ethanol is as follows:

• Ethanol burns readily with an almost invisible blue flame
• School laboratories use ethanol in spirit burners as it burns cleanly and without strong odours

Aerobic Oxidation

• Bacteria in the air (acetobacter) use atmospheric oxygen from air to oxidise the ethanol in the wine:

ethanol + oxygen → ethanoic acid + water

• The acidic, vinegary taste of wine which has been left open for several days is due to the presence of ethanoic acid
• This is what happens to wine when it is left open as the microbial oxidation of ethanol will produce a weak solution of the carboxylic acid, ethanoic acid, the same acid used in vinegar

Treatment with an oxidising agent

• Alcohols undergo oxidation to produce carboxylic acids when treated with oxidising agents
• When ethanol is heated with acidified potassium dichromate solution the ethanol oxidises to ethanoic acid
• The equation for the reaction is:

CH₃CH₂OH + [O]  →  CH₃COOH + H₂O

• The oxidising agent is represented by the symbol for oxygen in square brackets
• The reaction is slow so the mixture is heated to its boiling point for about an hour; to avoid the substances evaporating a condenser is placed above the reaction flask that prevents volatile liquids from escaping
• During the reaction the potassium dichromate turns from orange to green

Ethanol can be oxidised by heating it with potassium dichromate in sulfuric acid. The solution turns  from orange to green during the reaction