The Reaction in a Breathalyzer Test
An acidic chromium (VI) solution is shown to be yellow. After gargling with mouthwash containing alcohol, the demonstrator blows air through a straw into the solution. The alcohol from their breath reacts with dichromate, changing the solution from medium yellow to light green.
Transition metal compounds are often colored and a change in oxidation state of the metal often accompanies the color change. The alcohol on the demonstrator’s breath reduces Cr6+ to Cr3+, changing the solution color from yellow to green, while at the same time oxidizing the primary alcohol to a carboxylic acid. This demo can be shown to demonstrate the reduction of metals and the oxidation of organic compounds.