How does an alcohol meter work?

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Almost everyone has seen a driver carrying out an alcohol test by the police in films or even in reality. But how does an alcohol meter actually work? Even without a background in chemistry, you can easily understand how the device works.

The alcohol test works with an oxidation reaction.
The alcohol test works with an oxidation reaction.

The measuring process with the alcohol measuring device

Before explaining exactly which chemical reactions are used in an alcohol test, you should understand how the measurement process works with an alcohol measuring device.

  • The basic principle is to measure the percentage of alcohol that evaporates in the pulmonary arteries.
  • For this purpose, the test person blows his exhaled air into the device for about five seconds. The air is then directed into a rehearsal room with electronic sensors.
  • This is where a chemical reaction takes place called "oxidation". This generates electricity that is measured.

This is how measuring the alcohol level works

  • An alcohol meter works by using a chemical reaction called oxidation. The ethanol that the test person blows into the test tube with the exhaled air reacts with the chemicals it contains.
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  • The chemicals in the alcohol meter are a mixture that contains sulfuric acid and potassium dichromate.
  • If the ethanol now reaches the substances through the tube, the oxidation takes place, in the case of the one from the ethanol Ethanal is (chemists say the alcohol is "oxidized"), while the potassium dichromate produces chromium (III) sulfate: 3 CH3CH2OH + K2Cr2O7 + 4 H.2SO4 -> 3 CH3CHO + Cr2(SO4)3 + 7 H.2O + K2SO4
  • The reaction must take place in an acidic environment, which the sulfuric acid takes care of. In addition, this binds the water that is created during the reaction. If the water were not to be bound, the reaction would simply continue; the end product would be acetic acid.
  • Due to the chemical reaction, the packing bed is discolored for different "lengths". The alcohol level can then be read from the length.

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