Laboratory Experiment #8 Forensic Chemistry Determination of Breath Alcohol Content (BAC) PDF

Preview

Summary

Lab Report...

Description

Laboratory Experiment #8: Forensic Chemistry: Determination of Breath Alcohol Content (BAC)

Introduction: In the Determination of Breath Alcohol Content experiment, the Breathalyzer test will be used to determine the % BAC of the defendant of a case study. The objective of this lab is to collect quantitative and qualitative data in association with the Breathalyzer test to determine whether the defendant is guilty or innocent. If the percent BAC is found to be over 0.08%, then the defendant is found guilty for driving under the influence. The Breathalyzer test uses a photometric color comparator which analyzes the amount of alcohol in the bloodstream of a 52.5 mL of breath sample. This test is effective as it assumes that there is an equilibrium between the alcohol in the breath and alcohol in the lung air. Rather than a breath sample, solutions of ethanol are in place as stimulated breath samples and the SpectroVis Plus as a stimulated Breathalyzer. Analysis of the samples are based on the dichromate-ethanol reaction: 2 K2Cr2O7+ 8 H2SO4+ 3 C2H5OH → 2 Cr2(SO4)3+ 2 K2SO4+ 3 CH3COOH + 11 H2O Ethanol (alcohol) that is in the samples will react with yellow dichromate solution, which is acidified. There will be a change in concentration when the acidified yellow dichromate solution oxidizes the alcohol to acetic acid resulting in a decrease of yellow color. We will analyze this change with the SpectroVis Plus and use Beer’s Law to determine the concentration after the reaction has occurred. In this particular experiment Beer’s Law will be used in the following manner: A 1❑ C 1 = A2 C2

A1 = absorbance of known solution C1 = concentration of known solution A2 = absorbance of unknown solution C2 = concentration of unknown solution The molar absorptivity and path length of the cell are constants, this allows for the equation to be converted to absorbance and concentration. Using this equation, the change in concentration of the potassium dichromate will be calculated and the concentration will be used to determine the amount of ethanol (mg) in the sample. Then, it will be converted to % BAC using the relationship 0.25 mg ethanol = 0.10% BAC. This experiment utilizes quantitative and qualitative analysis using the SpectroVis Plus, stoichiometry, and Beer’s Law.

Experimental Section: Prior to measuring the absorbances and operating wavelengths to Solutions #1, #2, and #3, the SpectroVis Plus was calibrated with a pre-prepared blank sample. Determination of Operating Wavelength (Solution #1) In order to prepare the standard dichromate-H2O solution, a 10 mL pipet and pipettor was used to measure out exactly 10.00 mL of standard potassium dichromate solution which was then transferred into a clean 50 mL beaker. Using a 1 mL pipet and pipettor, 1.00 mL of distilled water was measured and transferred into the 50 mL beaker. The diluted solution was mixed thoroughly in the beaker and transferred to a cuvette. The cuvette with the standard dichromate-H2O solution was put into the spectrometer and had its absorbance spectrum measured. The operating wavelength was also recorded along with the absorbance at the operating wavelength. Determination of Absorbance of a Standard Dichromate-Ethanol (Solution #2) In order to prepare the standard dichromate-ethanol solution, a 10 mL pipet and pipettor was used to measure out exactly 10.00 mL of standard potassium dichromate solution and transferred into a 50 mL beaker. Using a 1 mL pipet and pipettor, 1.00 mL of standard ethanol solution was measured and transferred into the 50 mL beaker. The standard dichromate-ethanol solution was mixed thoroughly in the beaker and transferred to a cuvette. The cuvette filled with the standard dichromate-ethanol solution was put into the SpectroVis Plus and the absorbance at operating wavelength was recorded. Using these values and the values from the first part of the experiment, the concentration of the standard dichromate-ethanol solution was calculated. Determination of Absorbance of a Standard Dichromate-Potential DWI Defendants (Solution #3) In order to prepare the standard dichromate-potential DWI solution, a 10 mL pipet and pipettor was used to measure 10.00 mL of standard potassium dichromate solution and transferred into a 50 mL beaker. Using a 1 mL pipet and pipettor, 1.00 mL of the breath sample solution was measured and transferred into the 50 mL beaker. The standard dichromate-potential DWI solution was mixed thoroughly in the beaker and transferred to a cuvette. The cuvette filled with the standard dichromate-potential DWI solution was put into the SpectroVis Plus and the absorbance was collected at the operating wavelength. Using these values and the values from the first part of the experiment, the concentration of the standard dichromate-potential DWI solution was calculated. Results:

Table 1 - Analysis of the Three Dichromate Sample Solutions Solution

Wavelength (nm)

Absorbance

Concentration (mg)

1

445.9

0.669

6.25

2

445.9

0.616

5.75

3

445.9

0.540

5.04

Calculations Concentration of Solution #2: 5.75 mg 0.669 6.25 M = 0.616 C2 C2 = 5.75 mg Amount of K2Cr2O7 Consumed in Solution #2: 0.0017 mmol K2Cr2O7 consumed 6.25 mg−5.75 mg=0.50 mg 1g 1 mol K 2 Cr 2 O 7 1000 mmol 0.50 mg K 2 C r 2 O 7 =0.0017 mmol K 2 C r 2 O 7 1000 mg 294.185 g K 2Cr 2O 7 1 mol

(

)(

)(

)

Amount of C2H5OH Consumed (mmol) in Solution #2: 0.0025 mmol C2H5OH consumed 1mol 3 mol C 2 H 5 OH 1000 mmol 0.0017 mmol K 2 C r 2 O 7 =0.0025 mmol C2 H 5 OH 1000 mmol 2mol K 2 Cr 2 O7 1mol

(

)(

)(

)

Amount of C2H5OH Consumed (mg) in Solution #2: 0.1175 mg C2H5OH consumed 1 mol 46.07 g C 2 H 5 OH 1000 mg =0.1175 mg C 2 H 5 OH 0.0025 mmol C 2 H 5 OH 1000 mmol 1 mol C 2 H 5 OH 1g

(

)(

)(

)

% BAC of Solution #2 (0.25 mg ethanol = 0.10% BAC): 0.047% BAC 0.1175 mg C 2 H 5 OH 0.25 mg → x % BAC=0.047 % BAC = x % BAC 0.10 % BAC Concentration of Solution #3: 5.04 mg 0.669 6.25 M = C2 0.540 C2 = 5.04 mg Amount of K2Cr2O7 Consumed in Solution #3: 0.00411 mmol K2Cr2O7 consumed 6.25 mg−5.04 mg =1.21 mg 1g 1 mol K 2 Cr 2O 7 1000 mmol =0.00411 mmol K 2 C r 2 O 7 1.21 mg K 2 C r 2 O 7 1000 mg 294.185 g K 2 Cr 2 O 7 1mol

(

)(

)(

)

Amount of C2H5OH Consumed (mmol) in Solution #3: 0.00617 mmol C2H5OH consumed

0.00411 mmol K 2 C r 2 O7

3 mol C 2 H 5 OH 1000 mmol =0.00617 mmol C H OH ( 10001molmmol )( 2mol K 2 Cr 2 O 7 )( 1mol ) 2

5

Amount of C2H5OH Consumed (mg) in Solution #3: 0.284 mg C2H5OH consumed 1 mol 46.07 g C 2 H 5 OH 1000 mg =0.284 mg C2 H 5 OH 0.00617 mmol C2 H 5 OH 1000 mmol 1 mol C 2 H 5 OH 1g

(

)(

)(

)

% BAC of Solution #3 (0.25 mg ethanol = 0.10% BAC): 0.114% BAC 0.284 mg C 2 H 5 OH 0.25 mg = → x % BAC=0.114 % BAC 0.10 % BAC x % BAC Legal Brief Case Study Defendant: A female weighing 137 lbs −0.114 % BAC |0.10 % BAC |∗100=14 % error 0.10 % BAC

Error of Analysis=

The defendant is a female weighing 137 lbs. Upon calculating the % BAC in the defendant’s breath sample, the defendant was found to have 0.114% BAC. In most states, the acceptable % BAC is 0.08% or less. A violation of this rule, specifically with a % BAC higher than 0.08%, will result in conviction of a Class A Misdemeanor Driving With A Blood Alcohol Content of 0.08% or greater. This means that the defendant in question is guilty. The calculated % BAC had a 14% error. The defendant consumed around 3.27 bottles of 12 oz. beers. However, the period of time between the time when the accident happened and the time that the defendant was tested for their % BAC, the % BAC content could be lower than the actual value at the time of the incident. Conclusion: The use of the breathalyzer to test for % BAC content was stimulated with the SpectroVis Plus spectrometer and prepared solutions of ethanol. The purpose of this experiment was clearly addressed as we were able to calculate the concentrations and stoichiometrically calculate the % BAC in the defendant’s breath content. The final conclusion found the defendant to be guilty because their % BAC was found to be 0.114%. References: CHEM 107 Laboratory Manual, Department of Chemistry, Binghamton University, Binghamton, New York, 2019, pp. 127-131 What Is BAC? (n.d.). Retrieved November 4, 2019, from https://alcohol.stanford.edu/alcoholdrug-info/buzz-buzz/what-bac....