Experiment_3__Acidic_Molecules_Lab_ReportExperiment_3

Experiment_3__Acidic_Molecules_Lab_ReportExperiment_3 -...

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EXPERIMENT 3: ACIDIC MOLECULES (FORMAL) Introduction: ____10___ / 10 pts Procedure: ___5____ / 5 pts Data and Results _38_____ / 41 pts Table of Maximum Wavelength (λ max ) Data (3 points) 3 Table of Absorbance-Concentration Data (3 points) 3 Table of Absorbance-pH Data (3 points) 3 Table of Absorbance Data for Extract Samples (3 points) 3 Table of Calculated Concentrations for 8 Buffer Solutions (3 points) 3 Table of experimental and literature pKa values for bromothymol blue. (4 points) 1 Absorbance vs. Wavelength plot with the bromothymol blue spectrum obtained at pH 5.00 overlaid with the bromothymol blue spectrum obtained at pH 10.00. (6 points) 6 Absorbance vs. pH plot (6 points) 6 First derivative plot and corresponding spreadsheet used to construct the first derivative plot. (6 points) 6 Concentrations for 8 Buffer Solutions – Accuracy of Values (4 points) 4 Sample Calculations __10____ / 10 pts Molar absorptivity (5 points)
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Concentration of basic form of dye in sample. (5 points) Discussion __10____ / 10 pts A short discussion of the pKa of bromothymol blue that you experimentally determined and a discussion of how this value compares to the literature pKa value. Observations and conclusions from the experiment. Is the discussion section cohesive and well written. 5 Questions: ___21___ / 24 pts Question 1: 5 pts Question 2: 3 pts Question 3: 5 pts Question 4: 5 pts Question 5: 6 pts Other Deductions (i.e., Late Lab Report, incorrect formatting, etc…) - ______ Total Score ___94___ / 100 pts Experiment 3: Spectrophotometric Determination of the pKa of the Acid-Base Indicator Bromothymol Blue
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Pledge Introduction: The objective of this experiment was to first use spectrophotometry to determine the maximum absorbance wavelength for the acidic and basic forms of bromothymol blue and then to use the maximum absorbance wavelength of the basic form to measure the absorbance of eight different bromothymol blue buffer solutions. This data will be used to construct a graph of absorbance versus pH from which the Ka of bromothymol blue will be determined.
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Bromothymol blue is an acid-base indicator such that the acid and basic forms of the dye are different colors 1 . The acidic form is yellow, while the basic form is blue. As the pH of the solution changes, it is easy to view the color changes of the dye. The change in color is due to bonds in bromothymol blue reorganizing as the compound accepts or donates protons. Due to dissociation by water, the hydroxyl proton is lost converting bromothymol blue from the acidic state to the basic state. Through the process of electron delocalization, a shift in electrons and bonds allows for re-stability in the anion. When the oxygen regains a proton, the acidic form is seen again. The different colors that are seen are due to the absorption of light by the compound 1 . Absorption and irradiance both correspond to the general structure and makeup of
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Experiment_3__Acidic_Molecules_Lab_ReportExperiment_3 -...

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