Experiment_3__Acidic_Molecules_Lab_Report_rduong_duongExperiment3

Experiment_3__Acidic_Molecules_Lab_Report_rduong_duongExperiment3

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EXPERIMENT 3: ACIDIC MOLECULES (FORMAL) Introduction: ___5____ / 10 pts Procedure: ___2____ / 5 pts Data and Results ___41___ / 41 pts Table of Maximum Wavelength (λ max ) Data (3 points) Table of Absorbance-Concentration Data (3 points) Table of Absorbance-pH Data (3 points) Table of Absorbance Data for Extract Samples (3 points) Table of Calculated Concentrations for 8 Buffer Solutions (3 points) Table of experimental and literature pKa values for bromothymol blue. (4 points) 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) Absorbance vs. pH plot (6 points) First derivative plot and corresponding spreadsheet used to construct the first derivative plot. (6 points) Concentrations for 8 Buffer Solutions – Accuracy of Values (4 points) Sample Calculations ___4___ / 10 pts Molar absorptivity (5 points) Concentration of basic form of dye in sample. (5 points)
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Discussion ___7___ / 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: ___23___ / 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 ___82___ / 100 pts
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Experiment 3: Spectrophotometric Determination of the pKa of the Acid-Base Indicator Bromothymol Blue Richard Duong Lab Partner: Britt Mansfield November 19, 2009 Christopher Backlund Chem 241L, Section 420, Chapman Hall 125 The work presented in this report is my own, and the data was obtained by my lab partner and me during the lab period.
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Introduction The objective in this experiment is to find the Ka of bromothymol blue by using previous knowledge of acid-base properties and absorption characteristics. In turn, the pKa of bromothymol blue can be calculated from this. Due to the fact that bromothymol blue is a good acid-base indicator because of its structure, it appears yellow in the acidic form and blue in the basic form. This is possible because bromothymol blue has the ability to reorganize its structural bonds as it has a hydroxyl group that gives up a proton in the acidic form, while in the basic form it has electron delocalization. It is interesting to study this because using a spectrophotometer is much faster and more accurate than other methods in determining concentration. In order to fulfill the objective, a calibration plot will be created using absorbance values obtained from the spectrophotometer. The inflection point of this plot shows that the concentrations of both acidic and basic forms of bromothymol blue are equal, therefore from the Henderson-Hasselbauch equation pH = pKa. Additionally, since the inflection point is not seen
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Experiment_3__Acidic_Molecules_Lab_Report_rduong_duongExperiment3

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