Module 5 Lab Report

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2045L

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Chemistry

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Feb 20, 2024

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Module 5: Food Dyes Analysis in Commercial Products CHM 2045L

Introduction: The objective of this experiment is to use the principles of spectrophotometry for chemical analysis and determine the concentration of food dye in different commercial products. The different concepts of this experiment include visible spectrum and colors. The visible spectrum is the segment of the electromagnetic spectrum that is visible to the human eye. What is seen in this segment are colors. Red, orange, yellow, green, blue, indigo, and violet are what can be seen by the human eye. Another concept is ultraviolet-visible (UV-Vis) spectroscopy. This is a technique where light is passed through a sample at a specific wavelength in the visible spectrum. This helps to determine the transmission and absorbance of a solution. In this experiment, we will create a calibration curve. A calibration curve is created by preparing a set of standard solutions with known concentrations of the analyte. Then the instrument response is measured on the y- axis as the concentration of each solution is measure on the x-axis. Beer’s Law is an equation (A= ε l c) that is made by combining the relationships of the cell path length and the analyte concentration of absorbance. Experimental Methods: 1. Start with a red 40 stock solution. 2. Measure 10 mL of this solution into a graduated cylinder. 3. Transfer that into a 25 mL volumetric flask 4. Rinse the graduated cylinder with distilled water to ensure that all the stock solution is transferred. 5. Fill up the rest of the volumetric flask to the line with distilled water. 6. Cap the flask and invert the solution a few times until the solution is homogeneous. 7. Transfer the solution into a 50 mL beaker 8. Rinse the volumetric flask with distilled water to avoid cross contamination. 9. Take 10 mL of the diluted solution and put it back into the flask 10. Repeat earlier steps to perform serial dilution. 11. When done with dilution, take a small amount of all new solutions and place them into small, clear plastic cuvettes. 12. Calibrate the spectrometer.

13. After done calibrating, place a cuvette into the spectrometer to measure the absorbance of the solution. 14. Repeat with all solutions. Results: Concentration (M2) V2 (mL) M1 (Stock, M) V1 (mL) 0.0005 50 0.01 2.5 0.001 50 0.01 5 0.0025 50 0.01 12.5 0.0036 50 0.01 18 0.0051 50 0.01 25.5 Calibration Curve: Unknown drink: For the mystery red drink #1, I calculated the concentration to be 0.0062. For the mystery red drink #2 I calculated the concentration to be 0.0009. Discussion: In order to find the concentrations of the mystery drinks, I used Beer’s Law. The Epsilon in this equation would be the slope, which was 133.33. The path length (1 cm) was multiplied by the

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slope. After finding that, I divided the absorbance of both solutions by the product of the slope and path length. Potential errors that could happen in this experiment could be that the graduated cylinder does not get rinsed out correctly, causing cross contamination which would lead to the data being inaccurate. If I were to repeat this experiment, I would change the amount of dye and water in the solution. In this experiment, we mixed 10 mL of dye with 15 mL of water, but in the future, I would switch it around to 15 mL of dye and 10 mL of water. Conclusion: In this experiment, I determined the concentration of different dye solutions. This experiment proved that solutions with higher concentration have a higher level of absorbance. This ties back to the concept of the visible spectrum, since darker colors absorb more light. When the starting volume of the solution is higher, the end concentration is higher as well. By using Beer’s Law, I was able to identify the concentrations of the mystery drinks, by substituting the solutions’ absorbance and finding the slope of the calibration curve. References: Anderson, Laura. General Chemistry I Laboratory Manual . 2019. Blauch, David N. “Spectrophotometry.” Spectrophotometry: Beer's Law , https://chm.davidson.edu/vce/Spectrophotometry/BeersLaw.html Vo, Kevin. “2.1.5: Spectrophotometry.” Chemistry LibreTexts , Libretexts, 15 Aug. 2020, https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_ Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/02%3A_R eaction_Rates/2.01%3A_Experimental_Determination_of_Kinetics/2.1.05%3A_Spectroph otometry

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