Spectrophotometry DQ

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Texas A&M University *

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120

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Chemistry

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Feb 20, 2024

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Mackenzie Tijerina Section 617 Spring 2024 CHEM 120 Spectrophotometry: Pigments, light, and concentration Discussion Questions Make sure that your responses to these discussion questions is legible, if your responses are illegible they will not receive credit. We suggest that you type your responses. Using the data that you collected and wrote in your lab notebook during lab, organize your data into the required tables or graphs. Make sure that you format the table properly, i.e. include a title and labels for your columns, etc. Also make sure your plots are properly formatted and clearly labeled. 1. In a single table, tabulate your calibration curve data points. Make sure to include all proper labels and units for your solutions, concentrations, and Absorbance values. Also include your λ max value (2 points). Solution Concentration (M) Absorption at λ max = 664.8 nm Stock Solution 3.00 x 10 -4 0.353 Dilution 1 (50% concentration) 1.50 x 10 -4 0.175 Dilution 2 (25% concentration) 7.50 x 10 -5 0.096 Dilution 3 (12.5% concentration) 3.75 x 10 -5 0.061 Table 1: Calibration curve data points.
2. Attach plot for your calibration curve. Please format your graph including a title, axis-labels and units. Include your best fit line displaying the appropriate slope, y-intercept and R 2 value. (2 points). Chart 2: Calibration curve of the spinach solution using the λ max = 664.8 nm comparing the absorption verses concentration. 3. While doing the calibration curve plot for Spectrophotometry experiment, Zack and Mario had a conceptual discussion about how they should plot their data. Zach thinks that they should force the trendline for the absorbance vs concentration through the origin. On the other hand, Mario thinks (0,0) should be added. Is Zack or Mario correct? Using your data, explain why. Is adding (0,0) equivalent to forcing the trendline through the origine? Please provide your answer in paragraph form (6 points) I think that Mario would be right because with 0 absorption there should be 0 concentration. I think if we went with Zack’s idea this would be forcing the trendline through the origin because we see that the y intercept is (0, 0.01365) and this is the actual value that is given with the data we got from this experiment. y = 1,120.69565x + 0.01365 R² = 0.99829 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0 0.00005 0.0001 0.00015 0.0002 0.00025 0.0003 0.00035 Absorption Concentration (M) Calibration curve of Solutions (Absorbance vs. Concentration)
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