Question

Sketch the general shape/appearance of a “spectrophotometric titration curve” for the following system.  

You should label the axes of the graph, and show an approximate numeric scale (including units) on both axes.  
50.0 mL of 0.000100 M FeII(phen)32+ (aq)   + 0.01000 M Ce4+ (aq)   ===>
     FeIII(phen)33+ (aq) + Ce3+ (aq)
The substance being titrated, FeII(phen)32+, has ε = 12,100 M-1cm-1 at the wavelength of 510 nm that was used. During the course of the spectrophotometric titration, the absorbance of the solution is measured in 1.00 cm cells. The titrant Ce4+, as well as the products FeIII(phen)33+ and Ce3+ are all colorless at 510 nm (you may assume that ε = 0 M-1cm-1).  
Note: since [Ce4+] >> [FeII(phen)32+] in the titration, you may neglect the absorbance change that results from the “dilution effect” of the volume increase from addition of the titrant.

Answer 1

Titration,

We would consider complex Fe(phen)3^2+ as Fe2+ ion working ion,

thus,

Fe2+ + Ce4+ ---> Fe3+ + Ce3+

initial Fe2+ = 0.0001 M x 50 ml = 0.005 mmol

Titrated with, 0.01 M Ce4+

Absorbance = molar absorptivity (M-1.cm-1) x concentration (M) x path length (cm)

with,

molar absorptivity = 12,100 M-1.cm-1

path length = 1 cm

concentration = Fe(phen)3^2+ left in solution

Volume of Ce4+ (ml)          Absorbance

             0                                  1.21

           0.01                               1.186

           0.02                               1.1616

           0.04                               1.1132

           0.06                               1.0648

           0.08                               1.0164

           0.1                                 0.968

           0.2                                 0.726

           0.3                                 0.484

           0.4                                 0.242

           0.5                                    0

Plot volume Ce4+ on x-axis and absorbance on y-axis