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Protolytic Equilibrium Reaction Lab Report

700 Words3 Pages

ABSTRACT: This experiment investigated the effects of pH, temperature and ionic strength on the protolytic equilibrium reaction between the dianionic and anionic forms of fluorescein in aqueous solution. The effects were shown from the absorption and fluorescence spectra of each sample. The absorption and fluorescence spectra showed that the dianion species has the higher absorptivity and fluorescence than the anion species. Fluorescein solutions that contains more dianion species generated absorption and fluorescence spectra with higher peaks. The absorption spectra of all samples showed the highest peak at wavelength of around 488nm. The experiment found that the pKa value increased as the ionic strength increased within a range from 100.5±0.1mM to 500.8±0.5mM and the temperature decreased in a range from 22.3℃ to 65.0℃. By changing the pH of the fluorescein solution, ranging from 7.11 to 8.35, the pKa values did not stay …show more content…

This experiment was designed to analyze the effect of pH, ionic strength, and temperature on the protolytic equilibrium reaction between the dianionic and anionic forms of fluorescein. Since the dianion species has the strongest absorptivity and fluorescence,4 the more dianion species the solution contains, the higher absorption and fluorescence the spectra will show. Therefore, the effect of the parameters on the equilibrium can be shown from the absorption and fluorescence spectra. The approach was based on the following assumptions: fluorescein behaves according to the laws of equilibrium chemistry; the different ionic species have characteristic absorptivities and obey the Beer-Lambert law within the test concentration range; the presence of small amounts of fluorescein has a negligible effect on the buffer solution

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