Equilibrium Constants from Absorbance

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Measuring Equilibrium Constant from Absorbance Introduction Bromothymol blue, known for its highly defined color changes in reaction to different pH levels of its solution, is used as an indicator in weak acid and base solutions to help calculate titration curves and pH reactions. The equilibrium constant, or Kc, of a solution can be used in determining the amount of products created and the amount of reactant left over at the point of equilibrium. Three distinct acidic, basic, and neutral solutions of Bromothymol blue were created and measured along the wavelength spectrum and compared at a specific wavelength. The spectrum can then be used to determine an accurate Kc of the solution using the calculated equation given. Materials and Methods To first create the three distinct solutions, 50mL of phosphate buffer with a pH of 6.84 was poured into a 150mL beaker with 20 drops of 0.04% Bromothymol blue indicator. 5mL of the solution was then added to three separate 50mL beakers. 1mL of HCl was added to one of the three beakers and labeled ‘Yellow’, 1mL of NaOH was added to another and labeled ‘Blue’, and 1mL of distilled water was added to the last beaker and called ‘Green’. The spectrometer was prepared and left to warm up before calibrating it. Taking the three solutions prepared earlier, each was transferred to three separate cuvette while filling the fourth cuvette was filled with distilled water. The spectrometer was first calibrated with the blank and then each solution was measured, collecting its spectrum line of every solution onto one chart. The data was then correctly labeled and saved onto a CSV file. Results and Discussion As seen in figure 1 of the absorbance spectrum, it was found that the yellow [HBB] had its highest absorbance rate at lower wavelengths which then quickly dropped to zero after it passed 480nm. On the other hand, the blue

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