Chemistry Questions!!!urgent!!

[匿名]

2010-11-29 9:04 pm

The chemical method of analysis in determination of the blood alcohol content (%BAC) is:K2Cr2O7 + H2SO4 + C2H5OH → Cr2(SO4)3 + K2SO4 + CH3COOH + H2O

1. What are the stoichiometric coefficients for the reaction above? (please enter the coefficients with a coma between the numbers, e.g. 1,2,3,4)
2. During a Breathalyzer Test it was determined that 1.10mg of K2Cr2O7 was consumed by the above reaction. Calculate the number of milligrams of ethanol in the test sample.

3. Calculate the Blood Alcohol Content in this sample (%BAC).

please show me the whole processes, Thank you very much~

回答 (1)

己式庚辛

2010-12-02 10:37 pm

✔ 最佳答案

1.
first write out the half equations:
Cr2O7(2-) + 14H(+) + 6e(-) <======> 2Cr(3+) + 7H2O
CH3CH2OH + H2O <======> CH3COOH + 4H(+) + 4e-

balancing the no. of electrons, we have
2Cr2O7(2-) + 16H(+) + 3CH3CH2OH ------> 4Cr(3+) + 11H2O + 3CH3COOH
thus, adding the spectator ions:
2K2Cr2O7 + 8H2SO4 + 3CH3CH2OH
------> 2Cr2(SO4)3 + 11H2O + 3CH3COOH + K2SO4

2, 8, 3; 2, 1, 3, 11.

2.
mass of K2Cr2O7 = 1.10mg = 0.00110 g
no. of mole of Cr2O7(2-) = 0.00110 / (52x2 + 16x7) = 5.0926E-6 mole
mole ratio of dichromate : ethanol = 2:3
no. of mole of ethanol = 7.6389E-6 mole
mass = no. of mole x molar mass = 0.0003514 g
= 0.3514 mg

3.
here you only know the alcohol content in breathed air.
you'll need a conversion factor between content in breathed air and content in blood (since concentrations of ethanol aren't the same).

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