Complete these questions prior to attending lab. Some of the results will be useful in conducting the experiment, so you should record those results in the appropriate section of the lab as well. 1. In Part A, step 1, you are directed to set up the spectrophotometer for measurement of the FeSCN2+ product ion. a. Based on the spectra given here, what would be an appropriate wavelength for the measurement? Review Appendix I if necessary to again familiarize yourself with the issues related to this decision. b. Briefly explain your choice. Absorbance spectra for Fe³+ and FeSCN²+ 0.5 A 0.4 0.3 Absorbance A 0.2 0.1 0 400 0.02 M Fe³+ (dissolved in HNO3) 0.000048 M FeSCN² 500 600 wavelength (nm) 700 2. In Part A, step 4, you will experimentally determine the value of the molar absorptivity, &, for FeSCN2+ at your selected wavelength. Using the Beer-Lambert law, calculate an approximate value for & based on the spectrum of 0.000048 M FeSCN2+ provided above. The pathlength, &, for the cuvette is 1.00 cm. In Part A, step 4, you add about 0.6 g of solid Fe(NO3)39H₂O to a cuvette containing 2.00 mL of 2.0 M HNO3 and 2.00 mL of 0.000200 M KSCN. a. Assuming no reaction, what will be the initial molar concentrations of Fe³+ and SCN in the resulting mixture? (Don't forget the dilution effect!) b. Assuming the reaction: Fe³+ (aq) + SCN (aq) → FeSCN2(aq) goes completely to the right_ what will be the molar concentration of FeSCN2+ (aq) in the solution resulting from Part A step 4? (Think about the limiting reactant!)
Complete these questions prior to attending lab. Some of the results will be useful in conducting the experiment, so you should record those results in the appropriate section of the lab as well. 1. In Part A, step 1, you are directed to set up the spectrophotometer for measurement of the FeSCN2+ product ion. a. Based on the spectra given here, what would be an appropriate wavelength for the measurement? Review Appendix I if necessary to again familiarize yourself with the issues related to this decision. b. Briefly explain your choice. Absorbance spectra for Fe³+ and FeSCN²+ 0.5 A 0.4 0.3 Absorbance A 0.2 0.1 0 400 0.02 M Fe³+ (dissolved in HNO3) 0.000048 M FeSCN² 500 600 wavelength (nm) 700 2. In Part A, step 4, you will experimentally determine the value of the molar absorptivity, &, for FeSCN2+ at your selected wavelength. Using the Beer-Lambert law, calculate an approximate value for & based on the spectrum of 0.000048 M FeSCN2+ provided above. The pathlength, &, for the cuvette is 1.00 cm. In Part A, step 4, you add about 0.6 g of solid Fe(NO3)39H₂O to a cuvette containing 2.00 mL of 2.0 M HNO3 and 2.00 mL of 0.000200 M KSCN. a. Assuming no reaction, what will be the initial molar concentrations of Fe³+ and SCN in the resulting mixture? (Don't forget the dilution effect!) b. Assuming the reaction: Fe³+ (aq) + SCN (aq) → FeSCN2(aq) goes completely to the right_ what will be the molar concentration of FeSCN2+ (aq) in the solution resulting from Part A step 4? (Think about the limiting reactant!)
Principles of Instrumental Analysis
7th Edition
ISBN:9781305577213
Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Publisher:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Chapter21: Surface Characterization By Spectroscopy And Microscopy
Section: Chapter Questions
Problem 21.5QAP
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Transcribed Image Text:PRE-LAB QUESTIONS
Experiment 121
Complete these questions prior to attending lab. Some of the results will be useful in conducting
the experiment, so you should record those results in the appropriate section of the lab as well.
1. In Part A, step 1, you are directed to set up the
spectrophotometer for measurement of the
FeSCN2+ product ion.
a. Based on the spectra given here, what
would be an appropriate wavelength for the
measurement? Review Appendix I if
necessary to again familiarize yourself with
the issues related to this decision.
b. Briefly explain your choice.
0.5
A 0.4
0.3
Absorbance A
Absorbance spectra for Fe³+ and FeSCN²+
0.2
0.1
0
400
0.02 M Fe³+ (dissolved in HNO3)
E121-11
0.000048 M FeSCN²+
500
600
wavelength (nm)
700
2. In Part A, step 4, you will experimentally determine the value of the molar absorptivity, &, for
FeSCN2+ at your selected wavelength. Using the Beer-Lambert law, calculate an approximate
value for & based on the spectrum of 0.000048 M FeSCN2+ provided above. The pathlength, t, for
the cuvette is 1.00 cm.
3. In Part A, step 4, you add about 0.6 g of solid Fe(NO3)39H₂O to a cuvette containing 2.00 mL of
2.0 M HNO3 and 2.00 mL of 0.000200 M KSCN.
a. Assuming no reaction, what will be the initial molar concentrations of Fe³+ and SCN in the
resulting mixture? (Don't forget the dilution effect!)
3+
b. Assuming the reaction: Fe³+ (aq) + SCN (aq) → FeSCN2+ (aq) goes completely to the right,
what will be the molar concentration of FeSCN²+ (aq) in the solution resulting from Part A,
step 4? (Think about the limiting reactant!)
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Step 1: UV-visible spectroscopy and Beer Lambert law
VIEWStep 2: 1. Appropriate wavelength for the measurement and explanation
VIEWStep 3: 2. Determination of molar absorptivity
VIEWStep 4: 3. a) Determination of initial molar concentrations
VIEWStep 5: 3. b) Determination of molar concentration of FeSCN2+
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