Question

how to calculate the equilibrium concentration using absorption data and the best fit line from the beer's law

Answer 1

Using Beer’s Law To Find An Equilibrium Constant For Iron(III) Thiocyanato Ion Introduction For the reaction aA+ b B cC+ d D it has been shown in class that Keq = [C]c [D]d [A]a [B]b where Keq is the equilibrium constant for the reaction. The value of the equilibrium constant may be calculated from experimental data if the concentrations of both the reactants and products at equilibrium are known. Additionally, all equilibrium concentrations can be calculated if a single equilibrium concentration is known along with all other “initial” concentrations are known. The student will use spectrophotometry and Beer’s Law to determine this single equilibrium concentration. The equilibrium reaction studied in this experiment is formation of the iron(III) thiocyanato complex [Fe(SCN)+2] from the iron and thiocyanate ions: Fe+3 + SCN- Fe(SCN)+2 with the corresponding equilibrium expression: Keq = [Fe(SCN)+2] [Fe+3][SCN- ] The thiocyanate ion is colorless, the iron cation is slightly yellowish, but the iron(III) thiocyanato complex is a deep red-orange. Remember that many colored species will follow Beer's law: A = abc where A is the absorbance measured by a spectrophotometer, a is the absorptivity at a given wavelength of light, b is the path length and c is the concentration of the absorbing species. Since the wavelength and path length will be held constant, the relationship between absorbance and concentration should be linear.