Breathalyzer instrument

A Breathalyzer instrument contains two ampules, each of which contains 0.75 mg K2Cr207 dissolved in 3 mL of 9 M H2S04(aq). One of the ampules is used as reference. When a person exhales into the tube of the Breathalyzer, the breath is directed into one of the ampules, and ethyl alcohol in the breath converts Cr207 into Cr. The instrument compares the colors of the solutions in the two ampules to determine the breath alcohol content (BrAC), and then converts this into an estimate of BAC. The conversion of BrAC into BAC rests on the assumption that 2100 mL of air exhaled from the lungs contains the same amount of alcohol as 1 mL of blood. With the theory and assumptions described in this problem, calculate the molarity of K2Cr207 in the ampules before and after a breath test in which a person with a BAC of 0.05% exhales 0.500 L of his breath into a Breathalyzer instrument. 

Chemicals present in blood that are gases or possess a high degree of volatility diffuse passively into the alveolar air of the lung until they reach equilibrium. The concentration of these chemicals in the air phase is directly proportional to their concentration in blood, and the latter in turn is in equilibrium with the concentration of the chemicals in the tissues. This phenomenon can be applied to noninvasively monitor the presence and the concentration of gases and volatile substances in blood. A practical example of such application is the indirect measurement of alcohol present in blood by analyzing for ethanol in exhaled air with an instrument known as the Breathalyzer. 

The alcohol in beverages, hair spray, and mouthwashes is ethanol. Ethanol is a volatile liquid that evaporates rapidly at room temperature. Because of this volatility, drinking an alcoholic beverage results in a level of gaseous ethanol in the breath that is proportional to the level of alcohol in the bloodstream. About 50 percent of all automobile accidents that result in a fatality are caused by intoxicated drivers. Law officers can determine quickly whether a person is legally intoxicated by using an instrument called a breath analyzer, or Breathalyzer. 

Urinalysis is typically used as a preliminary test because it is less expensive and more convenient than the other tests. Saliva tests and breathalyzers are commonly used. Blood tests, although less frequently employed because they are generally more expensive and invasive, are more dependable, as are hair strand tests. A preliminary positive test using urinalysis must be confirmed by diagnostic tests completed in an analytical laboratory setting, which can take several days to complete. These diagnostic tests include the analytical instruments of gas chromatography (GG),... 

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