Spectrophotometry Lab

1. Spectrophotometry Lab Kevin Yu and Jack Rogness

2. What is spectrophotometry? • Measurement of material’s transmission properties • Function of wavelength • Can be used to determine the absorbance, concentration, and %transmittance of a substance

3. Objective • Design a lab that lets us determine solution concentration using a spectrophotometer

4. Materials • Test One: 20mL aqueous solution red dye, 20mL aqueous solution yellow dye, tap water, 2 500mL beakers, Cuvettes, Spectrophotometer, Kim wipes, plastic droppers • Test Two: 35mL stock dye solution (red), 2 500 mL beakers, 10mL graduated cylinder, cuvettes, spectrophotometer, plastic droppers, Kim wipes

5. Objective • Design a lab that lets us determine solution concentration using a spectrophotometer

6. Procedure – Test One • Rinse a cuvette with water, discard, and fill it two thirds full with water. This cuvette will only have water in it for the entire experiment. • Rinse the other cuvette with several milliliters of the stock aqueous solution of red food coloring, discard, and refill two thirds of the cuvette. • Record the absorbance of the solution from 350 nm to 540 nm at 10 nm intervals. • Rinse a cuvette with yellow food coloring, discard, and refill two thirds of the cuvette. Perform the same procedure as was used for the red food coloring. • Rinse the 10 mL graduated cylinder with several milliliters of the red solution, and discard the rinsing in a sink. Use the graduated cylinder to transfer 3-7 mL of red solution to a clean, dry 50 mL beaker; record the volume. Use the same graduated cylinder to transfer 3-7 mL of yellow solution to the beaker; again, record the volume. The sum of the two volumes should be at least 10 mL. • Swirl the contents of the beaker. This will be the orange solution. Repeat the procedure for data collection for the absorption spectrum, substituting the orange solution for the red solution.

7. Procedure – Test Two • Rinse a clean cuvette with 1-2 mL of the stock dye solution; discard the rinsing. Fill the cuvette about two-thirds full with stocky dye solution and clean the outside of the cuvette with a Kimwipe. • Using the Spectronics 20D, record the percent transmittance, %T, for the stock dye solution from 400 nm to 600 nm at 20 nm intervals. • Use a second cuvette two thirds filled with distilled water for the 100%T adjustment of the instrument at each wavelength. Remember to also set the 0%T adjustment at each wavelength, with the sample compartment empty and the sample compartment cover closed. • Determine the wavelength where the minimum %T more precisely. Record the wavelength where the minimum %T is observed. Discard cuvette contents and rinse. • Set the spectrophotometer at the wavelength where the minimum %T value was observed with the stock dye solution. Perform a 0%T and 100%T adjustment of the spectrophotometer at this wavelength. Record %T for solutions 1-4 and the unknown. • Obtain an unknown and record its number. Before measuring %T of the unknown, first rinse the cuvette with 1-2 mL of distilled water, discard that rinsing, then rinse with 1-2 mL of the unknown. After measuring the %T of the unknown, return the container with the remaining unknown to your lab instructor.

8. Appendix A-C

9. Appendix D-E

10. Discussion • Test One: Peaks, Ratio of volumes • Test Two: standard curve • Error, improvement • Moving On

11. Cited Works • Blauch, D. N. (n.d.). Spectrophotometry: Basic Principles. Retrieved from http://www.chm.davidson.edu/vce/spectrophotometry/Spectrophotometry.html

12. FIN