(The equation below is not balanced! Your first task is to balance it.) CH3CH2OH
ID: 22045 • Letter: #
Question
(The equation below is not balanced! Your first task is to balance it.)CH3CH2OH(aq) + Cr2O72(aq)----->CH3COOH(aq) + Cr3+(aq)
acidic solution
A Breathalyzer instrument contains two ampules, each of which contains 0.75 mg K2Cr2O7 dissolved in 3 mL of 9 mol L 1 H2SO4(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 (CH3CH2OH) in the breath converts Cr2O72 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.
(1a) If the test of such a breath sample yields a reading of 0.08%, what are the PARTIAL PRESSURE and mole fraction of CH3CH2OH in the breath of the person who was tested?
Explanation / Answer
balanced equation 10H1+ + CH3CH2OH + Cr2O7 2- => CH3COOH + 2Cr 3+ + 6H2O 2100 ml contains same alcohol as 1 ml of blood since, 100 ml blood contains 0.08 g alcohol 1 ml contains 8*10^-4 g alcohol since 2100 ml of air contains same as 1 ml blood 2100 ml air contains 8*10^-4 g alcohol 52.5 ml of air contains (8*10^-4)(52.5)/2100 = 2*10^-5 g alcohol 2*10^-5 g = 4.35*10^-7 mol no. of moles of air in 52.5 ml = 2.17*10^-3 mol mole fraction of alcohol = 2.004*10^-4 partial pressure of alcohol, p = mole fraction*total pressure = 20.2425 Pa Ans.
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