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Alcohols completely combust in the presence of oxygen to form carbon dioxide and water.

ethanol + oxygen → carbon dioxide + water

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

They combust incompletely when oxygen is scarce, producing water and either carbon monoxide or carbon (soot).

Oxidation of alcohols - higher tier

Methanol, ethanol and propan-1-ol can be oxidised to produce carboxylic acids. Methanol forms methanoic acid; ethanol forms ethanoic acid and propan-1-ol forms propanoic acid. Propan-2-ol may also be oxidised but you do not need to know about the product.

Alcohols only have to be exposed to the oxygen in the atmosphere for this to happen. The can also be oxidised using acidified potassium dichromate solution. They are mixed in a test tube and the mixture warmed in a warm water bath. Acidified potassium dichromate solution is an orange solution which changes to green when the alcohol is oxidised.

This can be used as a test for alcohols and only alcohols will show the orange to green colour change with acidified potassium dichromate solution.