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Determination of an Equilibrium Constant
Lab 5 -The Determination of an Equilibrium ConstantExperimental Data and Calculations:Part IBeaker[FeSCN2+]Absorbance11.6e-40.62421.2e-40.47538.0e-50.31044.0e-50.153Part IIBeakerAbsorbance (y)[FeSCN2+] atequilibrium (x)A0.2225.52e-5B0.3057.63e-5C0.3699.25e-5To calculate for x ([FeSCN2+] at equilibrium) I rearranged the equation  so that we are solving for x which gave me . To calculate the [FeSCN2+] at equilibrium for Beaker A I divided the difference of absorbance and the y intercept by the slope. .[pic 1][pic 2][pic 3]

Next, I calculated the initial concentration of each reactant in each of the three beakers so I could use an I.C.E chart to find for the equilibrium of each reactant and therefore the overall equilibrium constant for the reaction. To find the initial concentration I multiplied the concentration of the reactant by its volume in the beaker and divided that by the total volume in the beaker.Example: [pic 4]Because I now knew the initial concentration for each reactant and x,  I set up an I.C.E chart for each of the three beakers to solve for its equilibrium concentration. Because the reaction was going to the right (Fe3+ and SCN- were reacting to form FeSCN2+) I could minus the change in concentration (x) previously solved for, from their initial values of reactants and add that change in concentration to the products on the right.