Bromothymol Blue Lab Report

It is important to note that the goal of this experiment was to find the pKa value of bromothymol blue, a pH indicator commonly used in titrations. [UNC, 2017] The pKa is where the number of moles of acid to conjugated base are equivalent. To find this, both Beer’s Law and spectroscopy were utilized in an attempt to make graphs to show just where this value occurred. According to Sigma-Aldrich, the pKa of bromothymol blue is approximately 7.10. [SIGMA, 2017] The final pKa found experimental was also 7.10, as seen in figure five meaning that there was a 0.00% error between the literature and experiment results. In order to test the eight different pH solutions of bromothymol, we first found the maximum wavelengths that gave the highest absorption values – 1.407 at 615 nm for the basic pH of 5.02 and 0.591 at 433 for the …show more content…
Any other maximums on the graph are due to error. By finding the highest values, it allowed us to use the strongest wavelength to get the strongest and most accurate absorbance values possible. These values were critical for finding the pKa value, for they were used, specifically the basic pH solution’s, as the wavelength to test all eight test tubes for absorbance values. The following table and resulting graph can be seen in figures two and eight, respectively – of which the inflection point, or where the graph begins to rise, is considered the pKa value. Since this is difficult to see, however, the first derivative of table eight was taken to create a first derivative graph of which its main feature is a spike that is at the inflection point of figure nine – making it easier to pinpoint the pKa value found. Figure eight initially, however, was made from the table found in figure 2. The absorption values were found by taking the absorption value for the various solutions at the maximum wavelength value found from the highest pH solution