Question

CHEM 114 ‐ Lab Experiment 7 Equilibrium I – Determination of an Equilibrium Constant

3. In this lab, the measurement wavelength on the colorimeter was set at 470 nm.  This measurement wavelength was the best choice available on the colorimeter but it was not the best chemical choice for measuring the absorbance of FeSCN2+.   

a. In terms of instrument sensitivity, explain why the choice of wavelength on the colorimeter is important.  

b. Since the wavelength setting was not the ideal wavelength (max) for these absorbance measurements, do you expect the value for your absorbance readings taken by the colorimeter to be too high, too low, or accurate? Explain.

c. What experiment could you do, what data would you collect, and how would you analyze the data to determine the best setting for measuring the absorbance of FeSCN2+? Be sure to fully explain how your experiment and the resulting data would allow you to determine the wavelength of maximum absorbance for the FeSCN2+ complex.

Answer 1

3.

a. When the accurate wavelength max is used, the absorbance is maximum and less error in meaurement is possible. Higher the value, lower chances of errors exists. The sensitivity of the instrument such that error in measurement is minimal.

b. When wavelength max choosen is not the accurate one, the resulting absorbance values would be too low.

c. We should take absorbance readings at different wavelengths and see where we get maximum absorbance to calculate wavelength max for the complex.