Final Prep Answers
Final Prep Answers
Final Prep Answers
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Chem 155 <strong>Final</strong> review topics and questions:<br />
19. Circle the correct answer. In comparison to double-beam scanning<br />
spectrophotometers, diode array spectrophotometers are:<br />
Quality<br />
Spectrometer Type<br />
Diode Array Double Beam<br />
more accurate absorbance<br />
x<br />
more accurate wavelength<br />
x<br />
much faster<br />
x<br />
higher resolution<br />
x<br />
more complex<br />
x<br />
more expensive<br />
x<br />
20. What is the IR selection rule<br />
Dipole moment must change during vibration.<br />
21. What is the Raman selection rule<br />
Polarizability must change during vibration.<br />
22. Sketch the normal modes of vibration of the water molecule and indicate the<br />
Raman and IR activity:<br />
Mode Sketch IR Active Raman Active<br />
Symmetric stretch<br />
O<br />
Yes Yes<br />
H<br />
O<br />
Antisymmetric<br />
Yes<br />
No<br />
Stretch<br />
H H<br />
O<br />
Bend Yes Yes<br />
H<br />
H<br />
H<br />
23. The frequency of the Raman Stokes line for 488.0 nm laser light scattering from<br />
a 1500 cm -1 CO stretching vibrational mode.<br />
v Laser<br />
10 7 nm<br />
cm<br />
488.0nm<br />
v Laser 20492cm 1 v Vibration 1500cm 1<br />
v Raman v Laser v Vibration v Raman 18992cm 1 Stokes Line<br />
v Raman v Laser v Vibration v Raman 21992cm 1 Anti-Stokes Line
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