Question

Print Info The chemical method of analysis in determination of the blood alcohol content (%BAC) is: K2Cr207 + H2SO4 + C2H5OH Cr2(SO4)3 + K2SO4 + CH3COOH + H20 What are the stoichiometric coefficients for the reaction above? (please enter the coefficients without spaces and with a coma between the numbers, e.g. 1,2,3,4) 2,8,3,2,2,3,11 You are correct. Your receipt no. is 153-9906 > Previous Tries During a Breathalyzer Test it was determined that 1.40mg of K2Cr2O7 was consumed by the above reaction. Calculate the number of milligrams of ethanol in the test sample. 0.329 You are correct. Your receipt no. is 153-6017 Previous Tries Calculate the Blood Alcohol Content in this sample (%BAC). .0548 Submit Answer Incorrect. Tries 3/99 Previous Tries JLI.

i still need help on the last question. i tried equations but i keep getting it wrong. thank you

i believe it's moles over volume and the answer should be a percentage

Answer 1

Answer :

Find the coefficients:

The given chemical equation:

K₂Cr₂O₇ + H₂SO₄ + C₂H₅OH → Cr₂(SO₄)₃ + K₂SO₄ + CH₃COOH + H₂O

To write the stoichiometric coefficients, we need to balance the chemical equation.

Balanced chemical equation:

2K₂Cr₂O₇ + 8H₂SO₄ + 3C₂H₅OH → 2Cr₂(SO₄)₃ + 2K₂SO₄ + 3CH₃COOH + 11H₂O

Coefficients are nothing but the number of moles represented in the balanced chemical equation.

From the balanced chemical equation,

The coefficients are 2,8,3 for reactants and 2,2,3,11 for products.

Step 2

During a Breathalyzer Test, it was determined that the above reaction consumed 1.40mg of K2Cr2O7. Calculate the number of milligrams of ethanol in the test sample.

Given:

Mass of K2Cr2O7 = 1.40mg = 0.0014 g

The number of milligrams of ethanol?

Molar mass of K2Cr2O7 = 294.185 g/mol

Calculate the moles of K2Cr2O7 :

Moles = mass/ molar mass

Moles = 0.0014 / 294.185 = 4.76 X 10 -6

According to the balanced chemical equation,

2 mol of K2Cr2O7 reacts with 3 mol of ethanol

4.76 X 10 -7 moles of K2Cr2O7 reacts with ? mol. Of ethanol

On cross multiplication,

4.76 X 10 -6 X 3 / 2 = 7.14 X 10 -6

Convert moles of ethanol to mg:

1 mol of ethanol = 46 g

7.14 X 10 -6 = mass / 46

mass in grams = 0.000328 g

mass in mg = 0.328 mg

(c)

.25mg of ethanol = .10% BAC

so .25x=(.328)(.10)

= 0.131% (%BAC) Answer

Thanks