Chem 220 - Exam IVb – Spring 2011
Name
Date
SHOW ALL WORK!!!!!!
GOOD LUCK 
Points Earned
I.
II.
III.
IV.
BONUS
Total Points
I. Multiple Choice (15 pts TOTAL)
1. Absorption of IR radiation involves
a. rotational energy levels in the molecules ground state
b. vibrational energy levels in the molecules ground state
c. microwave energy levels in the molecules ground state
2. Fluorescence involves the excitation and emission of light based on the theory that
a. the emission wavelength and excitation wavelength are the same
b. the emission wavelength is longer than the excitation wavelength
c. the emission wavelength is shorter than the excitation wavelength
3. The principles behind a prism’s ability to separate light are based on
a. reflection
b. refraction
c. diffraction
4. If you want your molecule’s fluorescence to not be quenched then you should
a. increase temperature
b. decrease temperature
c. add O2
5. The main molecular characteristic required of a molecular that absorbs IR light is
a. pi bonds
b. lone pairs
c. net dipole
II. True or False (If False, Explain why in detail (15 pts total)
6. Absorption of visible radiation is a higher energy transition than absorption of ultraviolet
radiation.
7. The visible light wavelength range of the electromagnetic spectrum is 400 nm – 700 nm
with the 400 nm corresponding to blue light and 700 nm corresponding to red light.
8. FRAP stands for Fluorescence Recovery after Photobleaching.
9. The excitation beams and emission beams in a fluorescence spectrometer are at right angles
to each other.
10. Nitrogen gas is a global warming molecule.
IV. Short Answer (42 pts) Each question is worth 6 pts DO 7 of the following 9
11. You are on Spring Break and you are bragging to some new friends how you are pre-med
and that you study chemistry, physics, and biology. They are really impressed and one of
them asks you, “Hey, smarty, how does sunblock work?” You look at the back of the bottle
and notice that one of the main components is oxybenzone. What do you tell your new
friend?
BONUS (+3 pts) Name the 3 main functional groups in oxybenzone.
12. Explain why sulfur dioxide absorbs IR light by drawing the Lewis Structure (don’t forget to
explain!!)
13. a.(3 pts) Explain why fluorescein (structure below) is a molecule that fluoresces.
b. (3 pts) If the following is an image of a cell labeled with fluorescein, what color light does
fluorescein absorb? The cell in the image is the color red.
14. Explain using molecular orbital theory why not all p orbitals form pi bonds
15. a. (2 pts) How many absorption maxima would you expect to see in the UV/Vis spectrum of
benzene (structure below)? Explain.
b. (2 pts) What orbital transitions would the absorption(s) that you mentioned above
correspond to?
c. (2 pts) Would you expect another absorption if you replaced one of the hydrogens
with an amine group (NH2)? If so, what would this orbital transition be?
16. a. (3 pts) Explain 2 advantages of using the single beam photodiode array UV/Vis
spectrometer?
b. (3 pts) Explain 2 advantages of using the double beam UV/Vis spectrometer?
17. Draw the energy transitions for the following types of electromagnetic radiation
a. Visible
b. UV
E2
E1
v2
E0
v0
d. IR
c. Fluorescence
18. Devise an experiment to study a conformational change in a molecule (from conformation A to
conformation B). What technique would you use and how does it work?
Conformation B
Conformation A
19. Devise an experiment to study the diffusion of molecules from a cell’s membrane to a cell’s
nucleus. What technique would you use and how does it work?
III. Solve (28 pts TOTAL)
20.(16 pts TOTAL)
a. (10 pts) How much more energy would be required to excite a benzene molecule which
absorbs energy at a wavelength of 254 nm than a CO molecule which absorbs energy of a
wavenumber of 1600 cm-1? (h= 6.63 x 10-34 and c = 3.0 x 108 m/s)
b. (2 pts) Which molecule requires more energy: CO or benzene ?
c. (4 pts) Does your answer in b make sense? Explain.
21. (12 pts TOTAL)
a.(12 pts) Calculate the concentration in wt% of nicotine (MW 162 g/mol) in your saliva sample
of 0.0l00L if a diluted saliva solution (with water) of 10.00L total measures an absorbance of
0.09 and the following data for nicotine standards was collected.
Nicotine
Standards
1
2
3
4
Concentration
(ppm)
1
6
15
34
%
Transmittance
99
87
70
45
b. (BONUS +4 pts) What types of electrons in nicotine absorb UV light? Would you also
expect this molecule to absorb IR light? Why?
EXTRA BONUS!!
(BONUS +3 pts No partial credit) Explain why water would be a good solvent to use for
Raman spectroscopy.