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Bromocresol Green Equilibrium System Lab Report

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The objective of the Bromocresol Green Equilibrium System Lab was to determine if the equilibrium constant, K, was a true constant at constant temperature. To determine this, the value of the constant was found at different concentrations of HIn, HIn-, and at varying pH, which was used to determine the concentration of H+. K was found using the equation K= [HIn]/([In-][H+]). In order to be a true constant, none of the values of K found should differ from the average by more than two standard deviations. The values of K for solutions 1-5 and U were 4.39E4, 4.53E4, 4.23E4, 4.70E4, 6.35E4, and 4.03E4 respectively. The average K for the lab was found to be 4.71E4 and the standard deviation was 8.302E3. The range then that all experimental values of K must fall under is 3.05E4 to 6.37E4. All experimental values of K for this trial fell within the range. Therefore, K can be determined a true constant. The pH of the solution does not affect the value of the equilibrium constant, K. K is a ratio of the concentrations of the products and the reactants. A change in pH is simply due to a change in the concentration of Hydrogen ions and hydroxide ions. A change in concentration merely causes a shift in equilibrium towards either the products or reactants. It does not however change the value of the equilibrium constant at constant temperature …show more content…

Because of this, the experiment was done at constant temperature. If solutions 1-5 had been done at different temperatures, there would not have been a way to determine the effect of the change in temperature on the magnitude of the equilibrium constant. In order to be able to determine the magnitude, the original K value would first need to be determined. Once determined and both temperatures were measured, an experiment could be done to determine the K of the second

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