CHM120H5 Midterm: lab-4-determination-of-an-equilibrium-constant

The chemist I. N. Vino Veritas acquired the data shown below in a Job's method determination of the equilibrium constant for the formation of the iron (III) thiocyanate ion: Fe^+3_(aq) + SCN^-1_(ag) = FeSCN^+2_(aq). The equilibrium constant is given by K= [FeSCN^+2]/[Fe^+3][SCN^-1] = c_3/c_1c_2. Veritas's data at 480 nm: Absorbance, A = 0.303 for a solution with mu = 1/3. The stock solutions were at the same concentration of c_0 = 0.00100 M. The path length was b = 1.00 cm. Use this data to find the concentrations to four significant digits to avoid round off error, but report the equilibrium constant to three:

CHE 169 Exp. #3 The Determination of an Equilibrium Constant hemical reactions occur to reach a state of cquilibrium. The equilibrium state can be characterized by uaively delining its equilibrium constant, K In this experiment, you will determine the value of Ke or the reaction between iron (III) ions and thiocyanate ions, SCN Fe (aq)+ SCN (aq)FesCN (aq) he equilibrium constant, Kng, is defined by the equation shown below. To find the value of Ky, which depends only upon temperature, it is necessary to determine the molar oncentration of each of the three species in solution at equilibrium. The concentration will be determined by neasuring light that passes through a sample of the equilibrium mixtures. The absorbance of the colored olution is proportional to its concentration. The red pectrometer, an appropriate wavelength for maximum absorbance will be determined. FeSCN solution absorbs blue light. Using the n order to successfully evaluate this equilibrium system, it is necessary to conduct three separate tests First, a series of standard solutions of FeSCN will be prepared from solutions of varyin concentrations of SCN and constant concentrations of H' and Fe". The Fe concentration will be in side reactions (to form FeOH, for example). The excess of Fe" ions will make the SCN ions the limiting reagent, thus all of the SCN used will form FeSCN ions. The FesCN complex forms slowly, taking at least one minute for the color to develop. It is best to record absorbance readings no ter a specific amount of time has elapsed, between two and four minutes after preparing the equilibrium mixture. Do not wait much longer than four minutes to take readings, however, because the mixture is light sensitive and the FeSCN-ions will slowly decompose. series of solutions will prepared that have varied concentrations of the Fe' ions and Second, a new series of solutions will prepared that have varied concentrat the SCN ions, with a constant concentration of H ions. The concentrations o be comparable in concentra results of this test equilibrium constant for this reaction. f Fe" and SCN will tion with neither species in vast excess over the other. You will use the to accurately evaluate the equilibrium concentrations of each species, and thus the

The chemist I. N. Vino Veritas acquired the data shown below in a Job's method determination of the equilibrium constant for the formation of the iron (III) thiocyanate ion: Fe^+3 (aq) + SCN^-1(aq) = FeSCN^+2 (aq). The equilibrium constant is given by K = [FeSCN^+2]/[Fe^+3 ISCN^-1] = c_3/c_1c_2 Veritas's data at 480 nm: Absorbance, A = 0.303 for a solution with mu = 1/3. The stock solutions were at the same concentration of c_0 = 0.00100 M. The path length was b = 1.00 cm. Use this data to find the concentrations to four significant digits to avoid round off error, but report the equilibrium constant to three: Jack Jobs decided to use the method of continuous variation to determine the stoichiometry (n) of the complex formed between Ni^+ 2 and 1, 2 diaminoethane(ethylenediamine). For simplicity we'll abbreviate the ligand as EN and ignore the waters of hydration. Ni^+2 (aq) + n EN_(aq) = NiEN^+2 (aq) What is mu_max? What is n? What is the K expression?