Equipment used in an experiment to oxidise an alcohol (ethanol) with potassium dichromate, an oxidising agent. The flask at the bottom contains reduced green chromate (III) ions, and an aldehyde, ethanal, formed from the oxidation of ethanol. At top is a burette containing the orange dichromate solution. The change of colour from orange to green indicates that the chromate ions have been reduced, and thus that the oxidation of the alcohol has taken place.