aldayexperiment3 - appear in yellow whereas in strong basic...

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Acidic Molecules Maria Alexis Feby Capuno Alday Emily Welker February 8, 2011 Nathan Westcott 241L, Section 404, Room 404 “I pledge that I have not used someone else’s old or current lab report when writing this lab report. I pledge that I did not collaborate with any other students and that the report I submitted here contains my own ideas, thoughts, observations, calculations, data, conclusions and answers. Lastly, I pledge that the data presented in this report was collected by my lab partner(s) and myself during my scheduled lab period.” A sample of bromothymol blue solution will be analyzed by visible absorption spectra and Beer’s Law to evaluate the pKa and the spectra for the acidic form (HIn) and the basic form (In) at various pH levels for the lab experiment. An acid-base indicator such as bromothymol blue is a substance that displays different colors at different pH depending on whether the solution is acidic or basic. In a strong acidic solution, most of the indicator will be present in the form of HIn, causing the solution color to
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Unformatted text preview: appear in yellow whereas in strong basic solutions, most of the indicator will be in the In form, resulting the color to appear in blue. As the pH of a solution containing the indicator changes, the color shifts enabling one to see the changes from acid to base and vice versa. An acid-base indicator can be used to visually indicate the approximate pH of a sample. The approach used in this experiment involves taking advantage of the fact that the acidic and basic forms of the indicator absorb more strongly at different wavelengths. As the pH changes, the relative concentration of each form will change in accordance with the acid dissociation constant of the indicator and the resulting absorbance of each form will also change. The pKa of the indicator is obtained by the graphical analysis of the Absorbance at the wavelength of the maximum absorbance of In versus the pH data....
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aldayexperiment3 - appear in yellow whereas in strong basic...

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