Blood alcohol content (BAC) is often reported in weight-volume percent (w/v%). F
ID: 781175 • Letter: B
Question
Blood alcohol content (BAC) is often reported in weight-volume percent (w/v%). For example, a BAC of 0.10% correspondsto 0.10 gCH3CH2OH per 100 mL of blood. In Ontario, and the rest of Canada, the maximum legal BAC for fully licensed drivers is 0.08%. Estimates of BAC can be obtained from breath samples using a number of commercially available instruments including %u201CThe Breathalyzer%u201D. The original Breathalyzer instrument was based on the following oxidation-reduction reaction.(The equation below is not balanced! Your first task is to balance it.)
CH3CH2OH(aq) + Cr2O72%u2212(aq) -> CH3COOH(aq) + Cr3+(aq)
A Breathalyzer instrument contains two ampules, each of which contains 0.75 mg K2Cr2O7 dissolved in 3 mL of 9 mol L%u22121 H2SO4(aq). One of the ampules is usedas reference. When a person exhales into the tube of the Breathalyzer, the breath is directed into one of the ampules, and ethyl alcohol (CH3CH2OH) in the breath converts Cr2O72%u2212 into Cr3+.The instrument compares the colours of the solutions in the two ampules to estimate the blood alcohol content. The estimate of the BAC rests upon the assumption that 2100 mL of air exhaled from the lungs contains the same amount of alcohol as one millilitre of blood.
The Breathalyzer instrument typically tests 52.5 mL of exhaled breath. (a) If the test of such a breath sample yields a reading of 0.10 %, what are the partial pressure and mole fraction of CH3CH2OH in the breath of the person who was tested?Assume the atmospheric pressure and temperature are 101 kPa and 25.0 respectively. (b) Determine the maximum value of BAC that could be measured using the Breathalyzer instrument, as it is described above. [Note: A BAC of 0.40% is considered the lethal limit for
humans, that is, for a majority of adults, a BAC value of 0.40% causes death.]
Explanation / Answer
Ans: Balanced chemical equation is
3 CH3CH2OH + 2 Cr2O72- + 16 H+ = 3 CH3COOH + 4 Cr3+ + 11 H2O
this reaction is the result of one oxidation and 1 reduction reaction
This ratio describes the relationship between the alcohol content of breath and the alcohol content of blood at a given point in time. It defines the quantity of breath that would contain the same amount of alcohol as a given quantity of blood.
Numerous average values and ranges have been reported in the literature. For many years, the value of 2100:1 was accepted as the population average. This ratio indicates that 2100 parts of breath contain the same quantity of alcohol as 1 part of blood. Alternatively, 1 millilitre of blood contains 2100 times more alcohol than 1 millilitre of breath. This means that 80 milligrams of alcohol in 100 millilitres of blood are equivalent to 80 milligrams of alcohol in 210 litres of breath.
In this question ratio ia 10:1
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