Every year in United States about 25,000 people are killed and 500,000 more injured as a result of drunk driving. Various organizations have stepped up efforts to educate the public about the dangers of intoxication on America’s roads, and stiffer penalties have been imposed for such offenders.
The police often use a device called a breath analyzer to test drivers suspected of being drunk. The chemical basis of this device is a redox reaction. A sample of the driver’s breath is drawn into the breath analyzer, where it is treated with an acidic solution of potassium dichromate. The alcohol (ethanol) in the breath is converted to acetic acid as shown in the following equation:
3C2H5OH + 2K2Cr2O7 + 8H2SO4 -> 3CH3COOH + 2Cr2(SO4)3 + K2SO4 + 11H2O
In this reaction the ethanol is oxidized to acetic acid and the chromium in the orange-yellow dichromate ion is reduced to the green chromic ion.
The deriver’s blood alcohol level can be determined readily by measuring the degree of this color change (read from calibrated meter on instrument). The current legal limit of blood alcohol content in the United States is 0.1 percent by mass. Any value above this limit constitutes intoxication.