Name Section: omet Date: Post-Lab Questions Why is it important to run a blank s
ID: 228757 • Letter: N
Question
Name Section: omet Date: Post-Lab Questions Why is it important to run a blank solution to set the zero %T for both Parts I and II in this experiment? How would your results be affected if you did not run a blank? 1. 2. Briefly explain why you can assume that the equilibrium concentrations of FeSCN ion in solutions S2-S6 are equal to the initial concentration of SCN ion in these solutions. 3. Using your average value for K and the concentration/absorbance data for mixture S6, verify the assumption discussed in Question 2. You may need to solve a quadratic equation A student neglected to run the blank solution to set the zero %T in Part 1 and obtained the Beer's Law plot shown below 4, a) If the student used the plot as shown, how would their calculated values of Kag be affected? b) How could the student modify their plot to improve their results? 0.8 0.6 0.4 0.2 10 30 40 20 Concentration (Molarity x 103) 83Explanation / Answer
1)
When we use a spectrophotometer, we measure the sum of all light loss between the light source and the detector. Some of that light is simply not aimed directly at the detector, some of it is scattered by the corvette, some is absorbed by the corvette, some bounces off the detector instead of being absorbed by it, and some of the light is absorbed by your sample. We only need the light lost by absorption of your sample, so you run a "blank" cuvette in the machine first (water),and we call it as base line correction and the machine will internally save the absolute light value in its computer. Then when you put the sample in, the computer will automatically account for the light that was lost to all of the things that wasn't in your sample. If there is no any storage device in your spectrophotometer, then what we have to do is measure the absorption of your blank and then subtract the blank absorption from the measured sample absorption to calculate the actual absorption of your sample.
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