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. 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. 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. 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) The equilibrium concentrations of the three ions will then be experimentally determined. 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. Then, using ICE tables, the concentration of FeSCN2+ will be used to determine the equilibrium constant (Kc) of FeSCN2+. The FeSCN2+ ion produces solutions with a red color. 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. 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. If you could find the value and cite the source, it … 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. Keq = [FeSCN2+]/[SCN-][Fe3+] That is the equation for my experiment. 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. This is the reason that the order of SCN is Knowing the values of [Fe3+]eq, [SCN–]eq, and [FeNCS2+]eq, the value of Kc, the equilibrium constant, can be calculated. Their absorbances will be measured, and used to calculate the concentration of FeSCN2+. [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. These values will be substituted into the equilibrium constant expression to see if Kc is indeed constant. What is the accepted value of the equilibrium constant of Fe(SCN)2+ (ten bucks says you won't find it)? 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. In order to determine [FeSCN2+]eq, you will use the Colorimeter shown in Figure 1. 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. Five Kc values will be determined, and an average will be reported. I need the literature value for the Equilibrium Constant (Keq) of FeSCN2+, as well as the source of this value. 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. 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.