Data Analysis and Conclusions

                Through the use of UV/Visible spectroscopy combined with the calculations explained in the introduction, the average dissociation constant was found to be 1.2310×10-4 M for Bromophenol Blue, 1.3618×10-7 M for Bromothymol Blue 5.87x10-7 M for Bromocresol Purple, 2.35x10-5 M for Methyl Red, 4.93x10-4 M for Methyl Orange and 1.21x10-3 M for Methyl Yellow. These results are expected to be very accurate because for each acid-base indicator the combined spectra of its buffer solutions showed to have a very distinct isosbestic point.  An isosbesic point is the point at a specific wavelength in which the absorption spectra intersect and each substance has the same molar absorptivitiy. The clearly defined isosbestic point is supporting evidence that all of the buffer solutions were made correctly and the data obtained is accurate. If an isosbestic point was not found that data would not be accurate. When analyzing the absorption graphs for each acid-base indicator, Bromophenol blue and Bromocresol Purple show to have a more precise isosbestic points in which all of the spectra for each buffer solution unmistakably intersect. Although Bromothymol Blue, Methyl Orange, Methyl Yellow and Methyl Red also have distinct isosbestic points it is not as clear as Bromophenol blue and Bromocresol Purple’s points and therefore data for each of them could be slightly off.

                Although this experiment resulted in seemingly accurate and precise data, it is likely that there was some error. When the stock solutions of each acid-base indicator were made, not all of the indicator dissolved into solution. The solutions were filtered to eliminate any solid remaining but if a significant amount of solid indicator did not go into solution then the results could be altered. When there is not enough indicator in solution, the color change for each buffer solution with different pH values is less apparent. The absorption data obtained for that solution could then be slightly off. This lab also entailed the creation of many solutions. Due to the abundant amount of measurements done to create solutions for this experiment it is likely that measurement error occurred. Any measurement error would result in inaccurate data. The absorption graphs obtained for each species were very accurate will little deviation from the isosbestic point, therefore the experiment was very successful and there is only room for a small amount of improvement. To improve this experiment a few steps could be taken. More time could have been spent to insure that the acid-base indicators dissolved into solution. They could have spent more time in the sonicator or more 0.2M NaOH could have been added. In general more time could have been spent on creating all solutions to ensure that the correct amount of each substance was added. Overall, this experiment was very successful. The dissociation constants for Bromophenol blue, Bromothymol blue, Bromocresol purple, Methyl orange, Methyl red, and Methyl yellow were determined with significant accuracy and precision.