Complexmixture-Report-Sheet

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Jun 22, 2024

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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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