Chem 4101 – Fall 2010 EXAM 3 December 6, 2010 Write your name in the last page only ! !1! General Instructions: Time: 9:05 – 9:55 Points: 15 (maximum points for the course is 100) Bonus points (self-study): 3 points Allowed: One-sided, 8.5” x 11” crib sheet for equations; one calculator. Not Allowed: See Syllabus Regrading: Considered only if the exam was written in ink. 1. Give the name of one analyte relevant to your analytical problem. For each property below, select the best description for this analyte. [1.0 points]. Analyte Name: __________________________ Polarity: (a) Non-polar (b) Intermediate polarity (c) Polar In aqueous phase, pH 7.0, electrical charge: (a) neutral (b) negative (c) positive Molecular weight: (a) MW < 100 Da (b) 100 Da < MW < 1000 Da (c) 1000 Da < MW Thermal Properties: (a) Volatile at room temperature (b) Decomposes at <350 °C (c) Stable up to 350 °C Important functional groups: (a) ________________ (b) _________________Chem 4101 – Fall 2010 EXAM 3 December 6, 2010 Write your name in the last page only ! !2! 2. Assuming the limits of detection or the presence of matrix interferences are not relevant, mark (√) those techniques that are compatible with the separation of your analyte. Take into consideration your answers to Question 1. [2.0 points] (a) Gas Chromatrography (b) Reverse Phase HPLC (c) Hydrophobic interaction liquid chromatography (d) Ion-exchange liquid chromatography (e) Size exclusion chromatography (f) Capillary zone electrophoresis (g) MIcellar electrokinetic capillary chromatography (h) Capillary isoelectric focusing (i) Capillary gel electrophoresis (k) Affinity chromatography 3. Draw two linear voltammograms for Cr2+/ Cr3+in the same plot. Consider concentrations and potentials in your sketch. Label the axes. Eo = -0.408 V; Reference electrode: SCE; EoSCE = 0.25 V. [1.5 points] First voltammogram: Assume that the solution contains only 1x10-3 M Cr3+. Second voltammogram: Assume that the solution contains only 1x10-3 M Cr2+. (a) Identify the limiting currents. Identify in the plot and provide the value for the half-wave potential.Chem 4101 – Fall 2010 EXAM 3 December 6, 2010 Write your name in the last page only ! !3!(b) For each voltammogram, indicate whether it corresponds to either a cathodic or anodic wave. (c) For each voltammogram, write the electrochemical reaction that leads to the observed waves.Chem 4101 – Fall 2010 EXAM 3 December 6, 2010 Write your name in the last page only ! !4!4. Consider the following electrochemical cell: Pt|Fe3+ (4.00x10-2 M), Fe+2 (3.00x10-5 M) || Sn2+ (5.50x10-2 M), Sn+4 (3.5x10-4 M)|Pt Standard electrode potentials: For Fe3+/Fe2+, E° = 0.771V For Sn4+/Sn+2, E° = 0.154 V Using this nomenclature, one vertical line represents an interface, two vertical lines represent a salt bridge and the direction of the reactions is always from left to right. [1.5 points. Problem 22-7, part c, and example 22-8] (a) Calculate the electrochemical potential of this cell. (b) Is this a galvanic cell as written? Explain. (c) If this cell has an internal resistance of 4.0 Ω and initially shows a current of 0.10 A, what potential is produced (if it is a galvanic cell) or needed (if it is an electrolytic cell)?Chem 4101 – Fall 2010 EXAM 3 December 6, 2010 Write your name in the last page only ! !5!Chem 4101 – Fall 2010 EXAM 3 December 6, 2010 Write your name in the last page only ! !6!5. What is the order in which the following compounds would be eluted from an HPLC column containing a reverse-phase packing? Benzene, diethyl ether, n-hexane. If the mobile phase is made more polar what would you expect to happen? [1.5 points; problem 28-10] 6. Write a chemical reaction that represents the equilibrium that occurs in the analysis of Na2+ in an ion exchange column. Asssume that the cationic exchanger is sulfonic acid. Write the equilibrium constant and explain how it relates to the distribution constant. [1.0 points]Chem 4101 – Fall 2010 EXAM 3 December 6, 2010 Write your name in the last page only ! !7!7. Predict the order of migration of an anion, a cation, and a neutral molecule in a CE experiment in which electroosmotic flow is absent (i.e, a coated capillary) and the applied voltage is negative. Draw a hypothetical electropherogram for this separation. [1.0 points] 8. What will happen if one tries to separate DNA from different lengths by capillary zone electrophoresis? What mode of electrophoresis would be more suitable? Explain. [1.0 points]Chem 4101 – Fall 2010 EXAM 3 December 6, 2010 Write your name in the last page only ! !8!Bonus Points (Self – Study) 9. Give two advantages of automated analysis [1.0 Points, Section 33A-1] 10. Explain how flow injection analysis differs from chromatographic or electrophoretic separations[1.0 Points] 11. From the components below mark (√) those that have been implemented into microfluidic devices? [1.0 Points. Section 33C] (a) Peristaltic pumps (b) Mixers (c) Capillary electrophoretic channels (d) Intefaces for mass spectrometry (e) Laser-induced fluorescence detectors Name:_________________________________ Signature: ______________________ I used a Crib-Sheet? YES NO Total (Analytical Problem, questions 1-2): ___________________________________/3 Total (Topics covered in class, questions 3-13):_______________________________/12 Total (Self-study, Bonus, questions 14-16):__________________________________/3
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