Published on October 16, 2013

“Are you OK to drive, or should you call a cab? If you make the wrong decision, you may end up in jail or worse. You will meet lawyers. You will wear out your checkbook. And you will flinch when the car insurance bill comes. Or you might just blow off!” A Chemical Breathalyzer is often used as a device to test drivers suspected of being drunk by estimating blood alcohol content (BAC) from a breath sample. The chemical basis of this device is a redox reaction. The invention of the chemical breathalyzer provided law enforcement with a non-invasive test providing immediate results to determine an individual's BAC at the time of testing. It does not, however, determine an individual's level of intoxication, as this varies by a subject's individual alcohol tolerance. The BAC test result itself can vary between individuals consuming identical amounts of alcohol, due to gender, weight, and genetic pre-disposition.

With several types already in the market, each device has a mouthpiece, a tube through which the suspect blows air, and a sample chamber where the air goes to measure alcohol in the breath. To determine the amount of alcohol in that air, the color of the reacted mixture is compared to the color of a normal sample in another vial. The level of alcohol in the suspect’s breathing is estimated when the breathalyzer device then gives a readout that indicates the degree of color change.

Ethanol is the prime alcohol present in alcoholic beverages. There are many other chemicals that are classified as alcohols, but they have different names and chemical formulas. For example, rubbing alcohol is called isopropanol. Ethanol reacts with dichromate ion in acidic solution according to the chemical equation shown below:

3CH3CH2OH + 2K2Cr2O7 + 8H2SO4 _____> 3CH3COOH + 2Cr2(SO4)3 + 2K2SO4 + 11H2O
In this reaction, dichromate ion is converted to chromium ion. In solution the dichromate

Ion has an orange color, but the chromium ion is blue-green. This reaction is easily observed because the orange color disappears as dichromate ion is used up, and the blue-green color appears as chromium ion forms. In the breathalyzer test, the breath sample is bubbled into a vial which contains a solution of dichromate ion. Any ethanol in the breath sample reacts with the dichromate ion according to the reaction above, and the solution changes to a shade of golden yellow as a result of the reaction. The reacted mixture in this vial is compared to another vial which contains dichromate ion but no ethanol (so it will be bright orange). The difference in color between the two vials gives an indication of the amount of ethanol in the suspect’s breath.

However, the Chemical Breathalyzers are error prone and have a long way to go than the Drunk-o-meter. As per many forensic scientists, breath-analysis machines used by police forces are incapable of differentiating between mouth and blood alcohol, prone to human error and should not be used to issue immediate roadside driving suspensions. Like for example, drivers could have alcohol in their mouth from burping, and register a reading above 0.08 even though their blood-alcohol is below the legal limit. In such cases, machines cannot be considered reliable enough. The modern, portable method of measuring breath alcohol concentration is perfected by the Drunk-o-meter, a much advanced version of breathalyzers. Nonetheless, as they say, “You wishfully can see a man’s true character when he is drunk!” we have things like Breathalyzers that can bring you down to the self-righteous state of being sober, because once caught, it sure can hamper the chemistry of one’s day, one’s night and such imbalances that even a catalyst will never be able to fix.

Henceforth, Keep calm and be sober!