PROCEDURE
Part A: Preparing the Standard Curve
Make sure the spectrophotometer has been turned on at least 15 minutes before using. See Appendix F for directions on using the Spec 20.
Obtain 2 small, clean, dry beakers. Obtain 15 mL of 0.200 M Fe(NO3)2 in HNO3 in one beaker and 15 mL of 0.002 M KSCN in the other. Record the actual concentrations written on the bottles in your notebook.
Prepare a stock solution by pipetting 10.00 mL of 0.200 M Fe(NO3)2 in HNO3 and 2.00 mL of 0.002 M KSCN into a 25 mL volumetric flask. Add DI water to the calibration line, then mix thoroughly. This is your stock solution. Be sure to carefully record the starting and ending volumes in your pipet, don't just guess!
To create standard solutions for the standard curve, pipet the volumes below of your stock solution and DI water into large, labeled test tubes. Record the starting and ending volumes in your notebook. Assume volumes are additive. Before beginning, pre-rinse the pipet with a small amount of the stock solution. Mix each solution well.
Solution Stock Solution DLHO Standard 7.00 mL 3.00 mL Standard 2 5.00 mL 5.00 mL Standard 3 3.00 mL 7.00 mL Standard 1.00 mL 9.00 mL
Set the wavelength on the Spec 20 to 447 nm, the Amax of FeSCN2+. Fill a small test tube with DI water, wipe the outside of the test tube with a Kimwipe, then blank the spectrophotometer. Measure the absorbance of each standard in the same test tube used to blank the spectrophotometer. Measure