Marie Morin-Strom
Section 17
January 27, 2003
Senior Chemistry Discrepant Event Presentation
Title:
Alcohol Breath Analyzer Demonstration
Purpose:
To show how redox reactions have been used historically in every day life
For who:
Grade 12 U or C – Electrochemistry Unit
Materials:
Dichromate ion, sulfuric acid, water, test tubes, alcohol, straw, balloon.
Procedure:
Dissolve a small amount of potassium dichromate in 1-2 mL of water.
Add 5 drops of conc. H2SO4. Put 1-2 drops of Ethyl alcohol in a balloon
and blow it up. Slowly release the air through the solution using a straw.
The colour should darken to a greenish
Theory:
This reaction involves a reduction of the dichromate ion (CrVI) to
chromium (III). The reaction is given by:
8H1+ + Cr2O72- + 3C2H5OH -----------> 2Cr3+ + 3C2H4O + 7H2O
Although modern Breathalyzer devices use IR spectroscopy or gas
chromatography, law enforcement has in the passed used chromium
reduction devices as tests for alcohol consumption.
Hints for Success:
Make the solution fairly concentrated. A pale solution will not
change colour dramatically. Dichromate ion (Cr2O72-) can be
formed from a chromate ion(CrO4) by the addition of HCl to a
solution of potassium chromate. The formation will be marked by
a colour change from yellow to orange.
Safety Consideration: Chromium is a very dangerous heavy metal. It is toxic and should
be handled with care. Sulfuric acid can cause sever burns. It is not recommended that
this be used as a lab where students would be handling the chemicals.
References:
Patrick Gormley. (January 16, 2003) Alcohol Breath Analyzer
Demonstration. Retrieved: January 26, 2003
http://chem.lapeer.org/Chem1Docs/Breathalyzer.html