Spectrophotometry II Tutorial

Tutorial for Spectrophotometry II

EXAMPLE: Use the experimental data tabulated below to calculate Kd for the dissociation of the thiocyanatoiron(III) complex ion.

FeSCN2+ (aq)     —›     Fe3+ (aq)     +     SCN- (aq)        Kd = ?


Solution [Fe 3+]in [SCN -]in Absorbance
X 3.00e-1 1.50e-4 0.851
A 2.00e-2 1.50e-4 0.642
B 8.00e-3 1.50e-4 0.476
C 3.20e-3 1.50e-4 0.260
D 1.28e-3 1.50e-4 0.126



PROCEDURE:

  1. Highlight the default value (0.791) for the absorbance of Solution X in the column labeled "Absorbance."



  2. Enter your value (0.851) for the absorbance of Solution X.



  3. Enter your values for the absorbances of Solutions A, B, C, and D.



  4. Click the " Enter" button to display the plot.



  5. Click the button in the upper right-hand corner of the window, that contains the plot, to maximize the window size and move the scroll bar on the right side of the window to center the plot in the window.



  6. Click the " Linear Regression" button above the plot to fit a linear equation to the data. The values for the Kd, the standard deviation of the Kd, the ab (eb), the standard deviation of the ab (eb), and the correlation coefficient are displayed on the plot.



  7. To obtain a hard copy of the plot, press the "Print Screen" key on the keyboard. Next, click the "Start" button in the lower left corner of the screen and then select "Programs," "Accessories," and "WordPad."



  8. Click the "Edit" button in the tool bar at the top of the WordPad window.



  9. Select "Paste" from the pull-down menu to paste the plot on the WordPad page.



  10. Click the "File" button in the tool bar and select "Page Setup" from the pull-down menu.



  11. Click the "Landscape" Radio button in the Orientation section of the Page Setup on.



  12. Again click the "File" button in the tool bar and select "Print" from the pull-down menu to print a copy of the page with the plot.





RESULTS: