What is the chemical reaction that occurs in a breathalyzer?

1 Answer
May 9, 2016


Well, in the old days, they used orange crystals of potassium dichromate.


#2Cr_2O_7^(2-) + 3C_2H_5OH + 16H^+ → 4Cr^(3+) + 3CH_3COOH + 11H_2O#

That is breath alcohol would be oxidized by the orange dichromate to give green #Cr^(3+)(aq)#. I can still remember TV commercials of policemen administering the breath test, and then informing the delinquent driver the deadly words #"the crystals were green, sir!"#, meaning that the driver was in big trouble.

These days, they use solid state devices to test blood alcohol. I am told that when someone is nabbed for drink driving (using these tests) that they take a blood sample later so that they are certain of the alcohol level.