Chem 454/554 final exam
May 8, 2001
This web version will have a few changes in format, but the questionsa are the ones on last year's final exam. There may also be some problems with the placement of figures and tables.
- part I -- short answers ( answer 6 of 7) --- 7 pts each (42)
- part II -- chromatography (3 of 4) 15 pts each (45)
- part III -- electrochemistry (2 of 2, no choice here) 15 pts each (30)
- part II-- other instrumentation and methods (4 of 5) 15 pts each (60) ... total 177 pts
Part I-- (answer any 6 out of 7)
1. Write a Fourier Series
2. Wavelength and wave numbers ( cm-1)
- what is generally accepted as the visible region? ______ nm to _____ nm
- why does the conventional UV region extend only to 190 nm?
- what is the mid--IR region? __________ cm-1 to _____________cm-1
- what is the wavelength of 25,000 cm-1 radiation? __________ nm
3
. What is the molar extinction coefficient of the sample
- concentration: 4.0 x 10-4M in water
- wavelength: 425 nm
- spectrometer bandwidth: 15 nm
- cell length: 1.0 cm
- %Transmission: 27.54%
(part 1-- answer 6 out of 7)
4.
Monochromator Design:
- Increasing the area of the mirrors and the diffraction grating (keeping the same ruling or line spacing) has what effect:
- a. Effect on Spectral line width _____larger ____smaller _____ no
- b.Effect on Signal intensity ______higher ______lower _____no
- c. Effect on Dispersion: _____higher ______ lower _____no effect
- Increasing the slit width on the monochromator
- d. Effect on spectral Line with: _______wider ____ narrower ___ no effect
- e. Effect on Signal/Noise: ________higher ______lower _____ no effect
5. Which of these techniques provides useful surface analysis information:
| technique
| surface method
| bulk properties method
|
| IR Spectrum of a polymer film |
|
|
| Atomic Emission Spectroscopy (Flame) |
|
|
| Photoelectron Spectroscopy |
|
|
| Scanning Electron Microscope with X-ray detection |
|
|
| X-ray Diffraction Methods |
|
|
| Gas Chromatography |
|
|
6
. Mass Spectrometers-- Provide the names of four types of Mass Spectrometers
7. Return to Alphabet Soup-- what do the following acronyms represent:
-
AFM , LASER , ESCA
- XPS , NMR , HPLC , AA
- MALDI , ICP
, pH,
GC-MS
Part II. Chromatography
Answer
three of the
four questions below
II-1. Refer to the Figure (A Gas Chromatogram showing a single Gaussian Like peak-- not included on the Web version)
a. evaluate N and H (or HETP)
b. explain what N is
c. N goes through a maximum at some optimal flow rate (35-50 ml/min) : why?
(part II-- answer 3 of 4)
II-2.
What are the differences between packed columns and capillary columns in GC?
- a. how do the columns differ in construction
- b. how does the performance differ
- c. how does that alter the injection port requirements
II-3. Identify two commonly used detectors for GC (Other than mass spectrometers)
- a. briefly describe how each works
- b. what are the important differences in the performance of these detectors
II- 4. HPLC: Consider reversed phase chromatography
- (C18 bound phase; acetonitrile / water mobile phase)
- a. the sample contains a C10 phenol, a C10 alcohol and a terpene (a C10 hydrocarbon)
- what is the expected order of appearance of these species (why?)
- b. What does the phrase
Isocratic mean?
- What is the alternative to an Isocratic HPLC run?
- c. what is meant by a the phrase -- a C-18 bound phase?
- d. what is the most commonly used detector on hplc systems?
Part III-- electrochemistry (answer both 1 and 2)
II- 1. Voltammetry
- a. what is plotted (X-Y axes?)
- b. how would a plot look
- b1. for a slow scan with a dropping mercury electrode (Polarograph)
- b2. for a rapid, cyclic scan on a Pt electrode
- c. why is each step (peak) proportional to concentration of the species
II- 2. potentiometric methods
- a. electrodes --
- Briefly describe (sketch and label) a pH electrode and a reference electrode
- b. Nernst equation
- c. Briefly show how the Nernst Equation is used to determine a solution concentration
part IV-- instruments generally (answer 4 of 5 questions)
IV-1. A Mixture of two species is analyzed with a spectrophotometer
- Species 1 e = 1.25e3 at 425 nm and 0.73e3 at 620 nm (e3 is, of course, 103)
- Species 2 e= 0.27e3 at 425 nm and 3.27e3 at 620 nm
- A solution is measured at the two wavelengths
- At 425 nm A = 0.785 and at 620 nm A= 0.485
- What is the composition of the solution ?
(If you show what must be done, a numerical answer is not required)
IV-2. Briefly explain the techniques of
internal standard and
standard additions then tell why each is used (that is, what problems can the technique minimize or avoid)
IV-3. Describe the difference between
atomic and
molecular spectroscopic methods list several of each types, spectral
IV-4 . Which method(s) and instruments would be best for..... Briefly elaborate on your reasons for selecting the instrument...
- a. Determining the composition of a Cu- Ag- Zn- Pb- Sn - Mg alloy
- b. Determining the purity of an Aspirin synthesis (product quality)
- c. Determining if the air in a Chemical Storage Building meets safety regulations for volatile organic compounds.
- d. Checking canned peas for traces of Lead
- e. Determining the identity of a white powder confiscated in a police raid.
IV-5. Describe
one of the following (and it may
not be the subject of your paper)
- ATR sampling probe for IR Spectroscopy
- Stokes and Anti-Stokes Lines in Raman Spectroscopy
- Capillary Electrophoresis
end of the exam