Britannica
Sources used in this answer
Why does potassium dichromate change from orange to green in a breath-analyzer reaction?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
In a breath-analyzer, the color change from orange to green occurs due to an oxidation-reduction reaction.
When a person exhales into the device, any alcohol present in their breath reacts with a solution of potassium dichromate and sulfuric acid. During this process, the alcohol is oxidized, while the orange-colored chromium in the dichromate ion (where chromium is in the +6 oxidation state) is reduced to green-colored chromium (III) sulfate (where chromium is in the +3 oxidation state).123
The intensity of this color shift is directly proportional to the amount of alcohol in the breath sample, allowing the device to estimate the individual's blood alcohol concentration.2