Experiments

The ‘breathalyser’ reaction | 16–18 years

In association with , By and

Previews of the Breathalyser reaction student worksheet, teacher and technician notes, and a crime scene technician on a blue background

Source: Composite: © Monty Rakusen/Getty Images/Royal Society of Chemistry

Try this demonstration to recreate an early ‘breathalyser’ test, passing ethanol vapour through potassium dichromate. Includes kit list and safety instructions

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. 

Thanks for using the RSC’s education resources. You can view one resource per month as a visitor, or two resources per month when you’re logged in with a personal account.

A photograph of a teacher standing in a white lab coat, speaking with a class of children in a laboratory, is superimposed on a colourful background. Text reads "Teach Chemistry means support for classroom and staff room".

Register for Teach Chemistry for free, unlimited access

Registration is open to all teachers and technicians at secondary schools, colleges and teacher training institutions in the UK and Ireland.

Get all this, plus much more: 

  • unlimited access to resources, core practical videos and Education in Chemistry articles
  • teacher well-being toolkit, personal development resources and online assessments
  • applications for funding to support your lessons

Set up your Teach Chemistry account

Already a Teach Chemistry member? Sign in now.

Not a science teacher or technician based in the UK or Ireland? Don’t worry – you can also access all our resources with Royal Society of Chemistry membership.