2800labR2 - SPECTROPHOTOMETRIC DETERMINATION OF...

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SPECTROPHOTOMETRIC DETERMINATION OF DISSOCIATION CONSTANT BRITTNEY BROWN, KENNESAW STATE UNIVERSITY, KENNESAW, GEORGIA. SEPTEMBER 8, 2010 PARTNER: ERICA FRANCIS CHEM 2800L Due: October 4, 2010
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Brown 10/4/2010 INTRODUCTION: The purpose of this experiment was to determine the K a of an organic acid. An acid-base indicator is commonly used in chemical analysis to estimate the pH of a solution. In order to determine the K a of an organic acid the indicator, bromocresol green, was used. The indicator itself is a weak acid that changes color in response to changes in hydrogen ion concentrations, and therefore has a K a . For strong acidic solutions, the indicator was in the HIn form and showed a color change of yellow. In strong basic solutions, the indicator was in the In - form and showed a color change of blue. Lastly at intermediate pH values, the solutions were a mixture of both, the HIn and In - forms, depending on their relative amounts, and showed a color change of green. Changes in pH in accordance with the K a for the indicator resulted in changes in the absorbance for each form in the various solutions. Because the two forms absorb differently, the compound can be analyzed to obtain the pH to determine the K a for the organic acid. The reaction for this experiment is given by Reaction 1: (1) In the first experiment, a series of buffers solutions were prepared and characterized. The pH was calculated using Equation (1): = + [ -][ ] pH pKa log In HIn
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2800labR2 - SPECTROPHOTOMETRIC DETERMINATION OF...

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