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Chem 251 Exam 2 Fall 2003
NAME:
Questions on the exam are worth 6 points each unless otherwise noted. Show your setup for all
calculations.
Use the following chromatogram to answer question 1 – 3.
Peak Identification
1.
2.
3.
4.
5.
Cytidine
Uridine
Xanthosine
Guanosine
Adenosine
1. Given the HPLC chromatogram above for a mixture of nucleosides, calculate the resolution between
the Guanosine and Adenosine peaks using your best estimate of the required parameters from the
chromatogram.
2. Calculate the number of theoretical plates based on the Adenosine peak using your best estimate of
the required parameters from the chromatogram.
3. Assuming that Cytidine is more polar than Uridine which is more polar than Xanthosine, etc, was
this experiment run under normal or reverse phase conditions? (4 point question)
4. Short Answer: (2 points for each answer)
a. A resolution of _________ is the minimum for baseline peak separation.
b. Which HETP is better, 0.1 mm or 1.0 mm?
c. The carrier gas used with a TCD detector is: __________________
d. The most common HPLC detector is:_________________________
5. (4 pt quest) Give the best match for the terms in the first list with the characteristics in the second:
____ normal phase chromatography
A. Largest solute particles elute first.
____ reverse phase chromatography
B. Mobile phase is less polar than stationary phase
____ size exclusion chromatography
C. Most common bonded phase is C18.
____ ion-exchange chromatography
D. May require a salt gradient to elute solute
bonded to stationary phase.
6. A known mixture of compounds X and Y gave the following chromatographic results:
Compound
X
Y
Concentration (M)
0.0837
0.0666
Peak Area (arbitrary units)
423
347
Next, a solution containing an unknown concentration of compound X was analyzed: To 10.0 mL of
the unknown, 10.0 mL of a solution containing 0.146 M "Y" was added, and the mixture was diluted to
25.0 mL in a volumetric flask. This mixture yielded a chromatogram with two peaks with areas of 553
("X") and 582 ("Y"). What is the concentration of "X" in the unknown?
7. What is a FID and how does it work? Which type of chromatography is it used in?
8. Give definitions of and describe the differences between WCOT, SCOT, and PLOT columns.
9. Sketch a simple diagram of a GC.
10. Assume you are going to run an HPLC experiment. Once the column and detector are in place,
what experimental parameters might you change? Give 2 reasons why you might change the
experimental parameters. Are these parameters the same or different than in GC?
11. Given the following standard reduction potentials (25C):
Zn2+ + 2eˉ  Zn(s)
-0.762 V
Cu2+ + 2eˉ  Cu (s)
0.339 V
Calculate the voltage of the following cell under standard conditions:
Zn (s)  Zn2+ Cu2+  Cu (s)
12. What is the oxidizing agent in the above cell? (4 point question)
13. Calculate the voltage of the following cell: Zn (s)  Zn2+ (0.100M) Cu2+ (0.00500M) Cu (s)
14. Balance the following redox reaction (acidic conditions):
VO2+ + Sn2+  V3+ + Sn4+
15. Describe the Silver-Silver Chloride reference electrode and how it operates.
16. Describe how a glass pH electrode system works (assume it utilizes a combination electrode).
17. Short Answer: (2 points for each correct answer)
a. The voltage of a reference electrode is _____________________.
b. Ion selective electrodes _____________ (do or do not) involve redox processes.
c. The Nernst equation is used to find cell voltages under __________________________ conditions.
d. Reduction occurs at the ________________( cathode or anode) of a Galvanic cell.