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Carson Hill CHE 113-032 Karly Kindoll Rachel Stevenson 6 Mar. 2017 Using Absorbance to Find Chemical Equilibrium Introduction: Once a reaction reaches chemical equilibrium both reactants and products obtain concentrations that will not change anymore with time. To put it another way, chemical equilibrium occurs when the forward and reverse reactions are occurring at the same rate, making the concentrations of the products and reactants relatively constant during chemical equilibrium. When Fe 3+ and SCN - are mixed together they are automatically establish equilibrium with the product made: Fe(SCN) 2+ . The ultimate purpose of this experiment is to determine the equilibrium constant, K c , for this reaction. To be able to determine K c the concentrations of reactants and products must be found at equilibrium. This is done by creating an ICE table. The ICE table was determined from the figure below: Because of the reactants and products being a 1:1 ratio, the following equations can be used to find the concentrations of the reactants at equilibrium: [Fe 3+ ] eq = [Fe 3+ ] i [Fe(SCN) 2+ ] eq
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[SCN - ] eq = [SCN - ] i [Fe(SCN) 2+ ] eq To find [Fe(SCN) 2+ ] eq, a colorimeter will be used. Fe(SCN) 2+ makes a red colored solution. Red solutions absorb blue light well, therefore the blue setting on the colorimeter was used to determine the absorbance, A, of each solution. By making and measuring the absorbance of a standard solution where the concentration of the Fe(SCN) 2+ ions are known, with having a large concentration of Fe 3+ and a small concentration of SCN - , Le Châtelier’s principle states that a
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