1. Why should the solutions be prepared with 0.10M HCl used as solvent? a. What will happen to Fe3+ if the solution was not prepared using 0.10M HCl? b. Give the balanced equation for the 1st hydrolysis of Fe3+. c. What is the color of the product of 1st hydrolysis of Fe3+? d. What is the effect of the product of 1st hydrolysis to the absorbance of the solution?
Determination of Analytical Wavelength
2. Why should the solution with highest concentration be used to determine the analytical wavelength?
3. What was the analytical wavelength of FeSCN2+?
4. Relate the analytical wavelength to the color of the solution. Hint: Use a color wheel. 5. Why should we measure absorbance at the analytical wavelength?
6. What is the importance of the blank solution?
7. Why is KSCN added in large excess?
8. What is the concentration of FeSCN2+ for each solution? 9. Determine the corrected absorbance of the solutions. The corrected absorbance is the difference between the absorbance of the analyte solution and the blank. 10. Plot the corrected absorbance of the solution against the concentration of FeSCN2+. Determine the equation of the best fit curve. 11. Using the slope of the best fit curve, determine the molar absorptivity or the molar extinction coefficient, ε of FeSCN2+. The path length is 1cm. Compare the value you obtained to the theoretical value.
Determination of Unknown FeSCN2+ concentration
12. Why should the concentration of KSCN used be 0.002M instead of 0.20M which was the concentration used during calibration? 13. Why was another blank solution prepared and used for this part of the experiment? 14. Calculate for the corrected absorbance of the unknown solutions. 15. Determine the concentration of FeSCN2+ of each solution using the equation of the best fit curve. The concentration you will get here is the equilibrium concentration of FeSCN2+.
Determination of Kf of FeSCN2+
16. Determine the initial concentration of Fe3+ and SCN- of each unknown solution. 17. Calculate for the equilibrium concentration of Fe3+ and SCN-. 18. Show the expression needed to calculate for Keq or Kf of FeSCN2+. 19. Report the average Keq or Kf calculated and compare it to the range of the theoretical values for Keq of FeSCN2+.
Sources of errors
20. Determine all possible sources of errors. Identify whether the error is determinate or indeterminate. Also, if the error is determinate, identify if it is systematic, random or gross error. Report in tabulated form.
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