CHM110 Lab #4.docx - Campagna 1 Experiment 4...

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CampagnaExperiment 4:Spectrophotometric Determination of the DissociationConstant of an IndicatorRosa Giulia CampagnaLab Partner: Athena Capetanakis 1004764098CHM110 – PRA104TA: Jayasekera Buddhimathie Date Performed: November 5, 2018Date of Submission: November 12, 20181
CampagnaPurposeThe purpose of this lab was to determine the dissociation constant of the indicator bromophenol blue. This value was determined using the spectrophometer technique. The wavelength of the light of the acid and basic form of the bromophenol blue was determined. At various pH’s, the indicator solution was measured for absorbance. Using the absorbance allowed to calculate the dissociation constant. The molar absorptivity constant was calculated. Experimental Method1For the first half of the experiment a lab partner was worked with, and data was exchanged for the second half of the experiment since it was worked on individually. While working with a lab partner, 5.00mL of the 0.02% bromophenol blue stock solution was transferred into a 100.0 mL volumetric flask. Then 0.05 M KHP was added to the volumetric flask until the total volume reached exactly 100mL. The flask was the stoppered and then mixed well. Two 100 mL beakers were prepared each with 50mL of the solution, one being labelled A and the other being labelled B. The pH electrode was used to find the pH of one of the beakers since the pH of both beakers are the same at this step. Once the pH was recorded, the absorption spectrum was recorded for solution A on the interval of 380 nm to 650nm. The blank solution used was the KHP solution. The wavelength of the two absorption peaks were determined from the graph and recorded. The next part of the experiment was performed individually, one partner worked on solution A while the other partner worked on solution B. The treatment for solution A, first, 3 clean and dry sample vials were labelled according to the lab manual with A1, A2, and A3. The sample solution was then poured into each vial and then prepared according to instructions on 2
Campagnathe lab manual.1The pH of each solution was then recorded. Then, the absorbance of each of the solutions was recorded. The solution of A3 was diluted into three test tubes and then the absorbance of each solution was measured at the two absorption peaks (1 and 2) according tothe lab manual. The other partner was then responsible for solution B and prepared 3 clean and dry sample vials and labelled them according to the instructions in the lab manual.1The solutions in each sample vial were prepared using the concentrations outlined in the lab manual. The pH of each solution was measured and recorded. The absorbance of the solutions were recorded using the instructions from the lab manual. The solution B3 was diluted into three test tubes as outlinedin the lab manual and then the absorbance of each solution was measured at the two absorption peaks (1 and 2). Then the lab bench was cleaned as outlined in the lab manual.

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