Complexmixture-Report-Sheet

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REPORT SHEET: LAB 5 ANALYSIS OF A COMPLEX MIXTURE USING SIMULTANEOUS EQUATIONS Date: 3/15/2023 Student Name: Lyriq Lawyer Partner’s name: Aviahna Hall (2 points) Pre-lab Questions: 1. [2 points] Use of Beer’s law to solve for two components using simultaneous equations is based on [structural properties, proportional relationship, additivity property, chemical equilibrium, ionic strength] of the components in a given sample. Additivity Property 2. [2 points] In quantitative analysis where instruments are used, the signal (e.g. absorbance, pH, voltage) is the response due to [sample, ionic strength, temperature, analyte, blank]. Absorbance; analyte 3. [2 points] Based on the literature search, what are the pK a values of benzoic acid and protonated caffeine? Pka of Benzoic Acid = 4.19 Pka of Protonted Caffeine = -0.13 to 1.20 4. [2 points] What is the rationale for using a 0.01 M HCl as the solvent for preparing solutions in this lab? The 0.01 M HCl is used in the conversion of sodium benzoate into the acidic compound, benzoic acid. 5. [4 points] Solve for X and Y in the following simultaneous equations: 2.25 X + 6.55 Y = 10.65 7.25 X + 4.75 Y = 12.45 y = − 2.25 6.55 + 10.65 6.55 1

y = − 45 x 131 + 213 131 7.25 x + 4.75 ( − 45 131 x + 1.6259 ) = 12.45 x = 0.841 1.89 + 6.55 y = 10.65 y = 1.334 Y = 1.334, X = 0.841 Report: Concentration of stock Benzoic acid 99.7 and stock caffeine. .0213 (2 points) Figure 1. Overlay of the spectra of six calibration solutions of caffeine and benzoic acid used to determine absorptivity coefficients (in your figure, label each curve with an appropriate name) (4 points). 210 220 230 240 250 260 270 280 290 300 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Caffeine and Benzoic Acid Absorbance vs Wavelength B1 B2 B3 C1 C3 C2 Wavelength (nm) Absorbance Find the two wavelength of two maximum absorbances of the two analyte. Write down the wavelength below with all the digits obtained from your Excel data file. Highlight the two rows of your excel file (2 points)  max, 1 : 226.940155  max, 2: 272.9716492 2

Table 1. Raw data for benzoic acid absorbances obtained from Figure 1 at the two wavelengths. Concentrations are calculated from the stock solution and appropriate dilution factors (6 points). Solutions mg/L (ppm) Absorbance at  max, 1 Absorbance at  max, 2 B-1 3.96 mg/L 0.145164743 0.048944395 B-2 7.4775mg/L 0.301816851 0.10370896 B-3 9.97 mg/L 0.43665731 0.15132421 Sample calculation, mg/L Benzoic acid (4 points): M 1 V 1 = M 2 V 2 B 1 = ( 99.7 mg L ) ( 0.400 mL ) =( M 2 )( 10 mL ) M 2 = 3.96 mg / L Figure 2. Plot of Benzoic acid absorbances versus concentration at  max, 1 and  max, 2 to determine the calibration curves based on Table 1 data (each should be a linear curve with a linear equation and R 2 ) (4 points). 3 4 5 6 7 8 9 10 11 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 f(x) = 0.01 x R² = 1 f(x) = 0.04 x R² = 1 Benzoic Acid Concentraiton vs. Absorbance Max 1 Linear (Max 1) Max 2 Linear (Max 2) Concentration (ppm) Absorbance Table 2. Raw data for Caffeine absorbances obtained from Figure 1 at two wavelengths. Concentrations are calculated from the stock solution and appropriate dilution factors (6 points). 3

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Solutions mg/L(ppm) Absorbance at  max, 1 Absorbance at  max, 2 C1 3.20 mg/L 0.06704238 0.04824718 C2 7.46 mg/L 0.24319656 0.40885699 C3 10.65 mg/L 0.6235835 0.39808545 Sample calculation, mg/L Benzoic acid (4 points): M 1 V 1 = M 2 V 2 Sample Calculation for C1: ( 213 mg L ) ( .15 mL ) = ( x ) ( 10 mL ) x = 3.20 mg / L Figure 3. Plot of Caffeine absorbances versus concentration at  max, 1 and  max, 2 to determine the calibration curves based on Table 2 data (each should be a linear curve with a linear equation and R 2 ) (4 points). . 2 3 4 5 6 7 8 9 10 11 12 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 f(x) = 0.04 x R² = 0.94 f(x) = 0.05 x R² = 0.93 Max 1 Linear (Max 1) Max 2 Linear (Max 2) Concentration of Caffeine Absorbance 4

Figure 4. Spectra of solutions U1 and U2 (unknowns) prepared from the soft drink and the standards (in your figure, label each curve with an appropriate name) (4 points). . 210 220 230 240 250 260 270 280 290 300 0 0.2 0.4 0.6 0.8 1 1.2 Spectra of Solutions U1 and U2 U1 U2 Wavelength (nm) Absorbance Table 3. Raw data for the simultaneous equation solution. Absorbances of U1 and U2 are read at the specified wavelengths  max, 1 , and  max, 2 . Slopes are given in previous figures (calculated by Excel) (8 points). at  max, 1 at  max, 2 Benzoic acid slopes 0.042 0.0145 Caffeine slopes 0.0484 0.0415 Absorbance of U1 0.7519294 0.41460443 Absorbance of U2 0.491164744 0.507578373 Simultaneous equation sample calculation for U1 (4 points): 0.7519294 = 0.042 x + 0.0484 x 0.41460443 = 0.0145 x + 0.0415 y 5

x = 0.7519294 − 0.0484 y 0.042 0.41460443 = 0.0145 ( 0.7519294 − 0.0484 y 0.042 ) + 0.0415 y y = 6.21814 ( Caffeine ) 0.7519294 + 0.042 x + 0.0484 ( 6.21814 ) x = 10.73741 Table 4. (8 points) Results of Benzoic acid and Caffeine obtained from the simultaneous equation method after using the correct dilution factors . Benzoic acid Caffeine U1: mg/L drink solution 536 mg/L 3126.5 mg/L U2: mg/L Found 491 mg/L 312.6 mg/L U2: mg/L Expected 4.89 mg/L 5.21 mg/L % Recovery of U2 0.99% 1.67% Sample calculation for Benzoic acid in drink solution (4 points): M 1 V 1 = M 2 V 2 M 1 ( .2 mL ) = ( 10.73 mg L ) ( 10 mL ) = ¿ 535 mg/L Calculation of percent recovery of U2 (4 points): 4.89 491 x 100 = ¿ 6

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All significant digits in table 4 (2 points). Commentary of Figures and Tables (2 points). 7

Post-lab questions: 1. [4 points] Through inspecting the overlay (the figure below), which one suffers more interference between Benzoic acid and Caffeine? Explain Caffeine ends up suffering more interface because Aspartame’s absorbance overlaps with caffeine. 2. [3 points] Do your results (U1, U2, % recovery) reflect the extent of interference? Back up your answer. My results do reflect the extent of interference. The Benzoic acid received was much more than I expected and received low percentage for U2. The slope values were far from the true value given the calculated value. 3. [3 points] Could you have used other wavelengths other than  max ’s used in this lab to get better results? Using the max wavelengths enables us to pinpoint a specific location to increase accuracy. While using other wavelengths would increase the differentiation of our results therefor no we should not use other wavelengths. 4. [4 points] Why, in principle, is it possible to analyze caffeine and benzoic acid by UV detection? Would you analyze glucose by UV? Why/Why not? Both Caffeine and Benzoic Acid can experience UV detection due to conjugated pi electrons. Double bonds can absorb UV rays which we can detect. Glucose would not be used in spectroscopy because it lies on the visible light spectrum which gives off little absorbance compared to UV rays therefore it is more difficult to detect. 8