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I know that normal alcohol detectors work on the principle that potassium dichromate oxidizes alcohol . On what principle does an electric alcohol detector work?

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I believe you are referring to breathalyzers. When you breathe into a breathalyzer, any ethanol present in your breath is oxidized to acetic acid (the main component of vinegar apart from water) at the anode (there is a diagram below). At the cathode atmospheric oxygen is reduced. The overall reaction is the oxidation of ethanol to acetic acid and water. The electric current produced by this reaction is measured by a microprocessor and displayed as an approximation of overall blood alcohol content (BAC).

diagram of breathalyzer

This website can give you more information.

Hope this helps!

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  • $\begingroup$ What's the source of picture? $\endgroup$
    – Mithoron
    Jun 25, 2016 at 14:28
  • $\begingroup$ i.stack.imgur.com/IEQ9u.jpg (I found it while searching Google Images) $\endgroup$
    – auden
    Jun 25, 2016 at 14:30
  • $\begingroup$ They were already on imgur... there may be problems with rights, licence etc. $\endgroup$
    – Mithoron
    Jun 25, 2016 at 14:39
  • $\begingroup$ The other important factor that makes these devices acceptable by the courts, is that in the body alcohol is removed by a zero'th order reaction, i.e. linearly in time. (except at v low conc'n below any legal limit). This means that it is possible to calculate exactly what blood alcohol levels are, and to back calculate to earlier times. $\endgroup$
    – porphyrin
    Jun 27, 2016 at 19:31
  • $\begingroup$ Yes, that is very true. Thanks for adding that! $\endgroup$
    – auden
    Jun 27, 2016 at 23:11

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