[khall210]

Hi! My lab partner and I are having problems getting Absorbance values that are high enough for the second part of our Equilibrium Constant Lab. It is as follows:
0.002M Fe(No3)3, 0.002M NaSCN in HNO3, and 0.1M HNO3
We have 6, 10ml volumetric flasks. One is a blank, and the other 5 have been filled with 5mL of Fe(No3)3:
Blank should have 5mL of Fe(NO3)3, then filled to the line with HNO3
#1 should have 5mL of Fe(NO3)3 + 1mL of NaSCN added and then should be filled to the line with HNO3
#2 should have 5mL of Fe(NO3)3 + 2mL of NaSCN added and then should be filled to the line with HNO3
#3 should have 5mL of Fe(NO3)3 + 3mL of NaSCN added and then should be filled to the line with HNO3
#4 should have 5mL of Fe(NO3)3 + 4mL of NaSCN added and then should be filled to the line with HNO3
#5 should have 5mL of Fe(NO3)3 + 5mL of NaSCN added

We calibrated the spectrometer, which was set to 447nm, with the Blank solution, then began the experiment.
#1 Absorbance=0.53
#2 Absorbance=0.93
#3 Absorbance=0.134
#4 Absorbance=0.266
#5 Absorbance=0.318

Our instructor told us that all of our values should be double what they are. We didn't mix all of the flasks at one time, then try to get a reading. We mixed each one separately because we know that they are affected by light and deteriorate over time.  We repeated the process and let them sit for 3 mins, but that gave us only slightly higher Absorbency's on #'s 2-5. #1 was lower. We even made another Blank sample and tried to run them all again, but were unable to get higher values. We carefully rinsed the cuvette with HNO3 after each run and washed it with some of the solution from each flask twice. We even tapped out as much of the remaining wash from the cuvette, and wiped it with a Kemwipe before inserting it into the spectrometer. We placed a dot on the cuvette to make sure we were inserting it in the same way for every run. Any suggestions on how we can double these values?

[khall210]

Update:
I read through the laboratory procedure and I figured out where we went wrong. This was the second week in the lab. We should have used the Blank from Part A, which was a 25 mL volumetric flask with 10mL 0.1M Fe(NO3)3 filled to to the line with HNO3, when we calibrated the spectrometer! We just knew that we needed a new Blank solution, so we erroneously mixed a Blank solution with the 0.002M Fe(NO3)3.