The ‘breathalyser’ reaction | 16–18 years

In this experiment, show post-16 learners the reaction used in early forms of ‘breathalyser’. As air containing ethanol vapour passes through the acidified potassium dichromate solution, learners can observe a visible change from the orange of dichromate(VI), through brown, to the green of chromium(III) ions. Use the demonstration and student worksheet to provide context when teaching the properties of alcohols. The ‘breathalyser’ reaction is also a good opportunity to discuss the dangers of drinking and driving, although modern ‘breathalysers’ use electronic methods to detect and measure alcohol concentration. Learners will require prior knowledge of redox, oxidation states and properties of transition elements, in addition to the oxidation of alcohols.