An equilibrium constant can then be determined for each mixture; the average should be the equilibrium constant value for the formation of the FeSCN 2+ ion. If you could find the value and cite the source, it … In this experiment, the chemical reaction Fe 3+ (aq) + SCN – (aq) ß à FeSCN 2+ (aq) was studied to determine the equilibrium constant, K c. To determine this value, the absorptivity of several solutions were recorded using a colorimeter. I need the literature value for the Equilibrium Constant (Keq) of FeSCN2+, as well as the source of this value. These values will be substituted into the equilibrium constant expression to see if Kc is indeed constant. Experiment 8: DETERMINATION OF AN EQUILIBRIUM CONSTANT 77 Purpose: The equilibrium constant for the formation of iron(III) thiocyanate complex ion is to be determined. What is the accepted value of the equilibrium constant of Fe(SCN)2+ (ten bucks says you won't find it)? [FeSCN2+] K eq = —————– Equation 4 [Fe3+][SCN–] The value of K eq can be determined experimentally by mixing known concentrations of Fe3+ and SCN– ions and measuring the concentration of FeSCN2+ ions at equilibrium. This is the reason that the order of SCN is Five Kc values will be determined, and an average will be reported. In Part A of this experiment, you will prepare FeSCN 2+ solutions of known concentrations, measure their absorbances at 470 nm, and produce a calibration curve. The equilibrium concentrations of the three ions will then be experimentally determined. Fe3+(aq) + SCN–(aq) ←→ FeSCN2+(aq) Equation 3 Pale yellow Colorless Blood-red The equilibrium constant expression for this reaction is given in Equation 4. The FeSCN2+ ion produces solutions with a red color. Question: Pre-Lab – The Determination Of An Equilibrium Constant DATA TABLE Parts I And II Beaker [FeSCN2+] Absorbance 1 0.00 M 0.001 2 8.0 X 10-5 M 0.238 3 1.2 X 10-4 M 0.344 4 1.6 X 10-4 M 0.435 5 2.0 X 10-4 M 0.530 Unknown, Part II 0.302 Insert Excel Absorbance Vs Concentration Curve Here Include Linear Least Squares Fit Too 1. To prepare the standard solution, the complex is formed from Fe 3+ and SCN- ions, using a very high concentration of Fe 3+ ions. Introduction: In the previous week, we qualitatively investigated how an equilibrium shifts in response to a stress to re-establish equilibrium. Then, using ICE tables, the concentration of FeSCN2+ will be used to determine the equilibrium constant (Kc) of FeSCN2+. The value of K c will be too low; the lower absorbance reading indicates a lower [FeSCN2+] than actually existed before the fading occurred, so substitution of a lower [FeSCN2+] into the equilibrium expression will result in a lower value of K c. One point is earned for the correct prediction. MATERIALS Macintosh or IBM-compatible computer 0.0020 M KSCN Serial Box Interface or ULI 0.0020 M Fe(NO 3) 3 (in 1.0 M HNO 3) initial = 0.00020 M, and an equilibrium concentration, [FeSCN 2+] eq = 0.0000195 M, the ICE table will be: Fe3+ + SCN− ⇔ FeSCN2+ Initial 0.00100 0.00020 0 Change -0.0000195 -0.0000195 + 0.0000195 Equilibrium 0.00098 0.00018 0.0000195 The initial concentration of FeSCN2+ is zero because the reaction has not yet started, but at One point is earned for the correct justification. Keq = [FeSCN2+]/[SCN-][Fe3+] That is the equation for my experiment. The actual concentration of the FeSCN 2+ complex present at equilibrium in a solution may be obtained by comparing its color with standard solution, in which the concentration of FeSCN 2+ is known. FeSCN2+ for any of the equilibrium systems can be found by: [FeSCN2+] eq = A eq A std X [FeSCN2+] std ... you can now calculate the value of K c, the equilibrium constant. Knowing the values of [Fe3+]eq, [SCN–]eq, and [FeNCS2+]eq, the value of Kc, the equilibrium constant, can be calculated. In order to determine [FeSCN2+]eq, you will use the Colorimeter shown in Figure 1. The thiocyanate ion acts as an isothiocyanate ligand to Fe3+, in other words, the iron binds to the nitrogen atom of the ligand not the sulfur atom. Their absorbances will be measured, and used to calculate the concentration of FeSCN2+.