Finding the Equilibrium Constant of Bromothymol Blue with Spectrophotometry

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Introduction There are varied ways that chemists can determine an equilibrium constant value of a reaction. One of them is by way of a spectrophotometer, as demonstrated in the experiment. The Equilibrium Constant, Ka, for Bromothylmol Blue is the point at which the rate of the forward and reverse reactions are equal to each other and when the concentrations of the products/reactants no longer change. It is important for scientists to know a certain equilibrium constant value so that they can determine the ratio of the products to reactants in a given reaction when at equilibrium. Materials and Methods To begin, .4001 grams of Na2HPO4 and .4081 grams of NaH2PO4 solid was added together into a clean, dry 150 mL glass beaker. Then, approximately 50 mL of distilled water was added to the mixture, and the phosphate solids were stirred until fully dissolved. The last ingredient added to the beaker was exactly 20 drops of the liquid .04% bromothymol blue solution. Using the Vernier pH probe, the initial pH of this soluton was found to be 7.10. After obtaining three clean, dry 50mL glass beakers (Labeled one of each “yellow,” “blue,” and “green.”) approximately 5.00 mL of the solution from the 150mL beaker was added to all three with a volumetric pipet. Taking a 1.0 mL volumetric pipet that had been rinsed with 1.0M HCl, 1.0 mL of 1M HCl solution was added to the “Yellow” 50mL beaker containing the phosphate solution. The pipet was then rinsed with distilled water and then rinsed again with 1M NaOH, before 1.00 mL of NaOH solution was measured and added to the “Blue” 50 mL beaker. Lastly, the pipet was once again rinsed thoroughly with distilled water and 1.00 mL of distilled water was added to the last 50 mL beaker, labeled “Green.” To conclude this part of the experiment, four dry cuvettes were labeled “Blank,” “Y,” “B,” and “G” before being filled with

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