Ethanol and Oxidation Notes

Ethanol

Ethanol Oxidation

  • Ethanol can be oxidized by:

    • Burning in air or oxygen (complete combustion).

    • Reaction with oxygen in the air to form ethanoic acid (microbial oxidation).

    • Heating with potassium dichromate(VI) in dilute sulfuric acid to form ethanoic acid.

Oxidation of Alcohols

  • Oxidation is the losing of electrons.

  • Combustion involves the complete oxidation of the alcohol molecules.

  • Alcohols can react with oxidizing agents, which selectively oxidize the carbon atom attached to the OH group, keeping the carbon skeleton of the molecule intact.

  • Alcohols can be oxidized into other organic compounds.

Combustion

  • When alcohols are burnt in air with a plentiful supply of oxygen, they will undergo complete combustion to produce water and carbon dioxide.

  • Oxidation is the gaining of oxygen or the loss of electrons.

  • Balanced symbol equation for the combustion of propanol needs to be written.

Combustion Energetics - ΔH_c

  • Different alcohols release different amounts of energy when burned in oxygen.

  • Research the link between carbon chain length and enthalpy of combustion.

  • Explain the trend through calorimetry data.

Microbial (Aerobic) Oxidation

  • Bacteria in the air (acetobacter) use atmospheric oxygen from the air to oxidize the ethanol in wine:
    ethanol + oxygen \rightarrow ethanoic \, acid + water

  • The acidic, vinegary taste of wine left open for several days is due to the presence of ethanoic acid.

  • The microbial oxidation of ethanol will produce a weak solution of the carboxylic acid, ethanoic acid, the same acid found in vinegar.

Oxidizing Agents

  • Ethanol can be oxidized using acidified potassium dichromate(VI).

    • This is a bright orange solution owing to the presence of Cr(VI), which is reduced to green Cr(III) as the alcohol is oxidized on heating.

  • When writing the equations, the oxidizing agent is sometimes shown simply as '+ [O]'.

  • The equation for the reaction is:
    CH3CH2OH + [O] \rightarrow CH3COOH + H2O

  • 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.