Show all work for full credit. You would like to determine the equilibrium const
ID: 1084491 • Letter: S
Question
Show all work for full credit. You would like to determine the equilibrium constant for the binding of a ligand to a metal ion: M" + L- ML". where K = [([ML2+])/([M3+)(L-])]. The ML2+ complex has a unique absorbance in the visible region, so its concentration at equilibrium can be determined by measuring the absorbance of the solution at an appropriate wavelength. An ICE table can be used to determine the concentrations of M and L from their initial concentrations and the concentration change in going to equilibrium. The following experiment is carried out first to determine the extinction coefficient of the complex at the wavelength chosen. I) Calculate the complex concentration in each solution and then its extinction coefficient. Solution Metal 0.1M 0.0011 M Solution m)(mL) 0.200 M 0.1 M LigandConcentration Absorba) Extinction Coefficient Meta HNO on 5.0 5.0 5.0 2.0 5.0 5.0 1.0 2.0 3.0 4.0 5.0 0.113 0.227 0.337 0.431 0.562 4.0 3.0 1.0 0.0 Plot the absorbance versus the solution concentration and determine the slope and intercept of the resulting line.Explanation / Answer
Reaction,
M3+ + L- <==> ML2+
Table 1
Solution A, complex concentration = 0.0011 M x 1.0 ml/10 ml = 1.1 x 10^-4 M
Solution B, complex concentration = 0.0011 M x 2.0 ml/10 ml = 2.2 x 10^-4 M
Solution C, complex concentration = 0.0011 M x 3.0 ml/10 ml = 3.3 x 10^-4 M
Solution D, complex concentration = 0.0011 M x 4.0 ml/10 ml = 4.4 x 10^-4 M
Solution E, complex concentration = 0.0011 M x 5.0 ml/10 ml = 5.5 x 10^-4 M
Plot,
concentration on x-axis and absorbance on y-axis
the slope of line gives molar extinction coefficient
slope = (0.337 - 0.227)/(3.3 x 10^-4 - 2.2 x 10^-4)
= 1000 M-1.cm-1
Now using,
equilibrium concentration of complex = absorbance/molar extinction coefficient
Table 2
Solution F
[M3+]init = 0.0023 M x 3 ml/10 ml = 6.9 x 10^-4 M
[L-]init = 0.0011 M x 7 ml/10 ml = 7.7 x 10^-4 M
[ML2+]eq = 0.286/1000 = 2.86 x 10^-4 M
[M3+]eq = (6.9 x 10^-4 - 2.86 x 10^-4) = 4.04 x 10^-4 M
[L-]eq = (7.7 x 10^-4 - 2.86 x 10^-4) = 4.84 x 10^-4 M
K = [ML2+]eq/[M3+]eq.[L-]eq]
= (2.86 x 10^-4)/(6.9 x 10^-4)(7.7 x 10^-4)
= 1463
Similarly K values can be calculated for other solutions.