Chemistry 325 Instrumental Analysis February 3, 1995 1 Exam 1 ...

Chemistry 325 Instrumental Analysis February 3, 1995
g. A D 2 arc lamp
(1) is the most widely used source of visible photons.
(2) is the most widely used source of ultraviolet photons.
(3) is the most widely used infrared source.
(4) has a continuous output spanning the ultraviolet and visible ranges.
h. Double beam spectrometers
(1) employ an optical chopper or beam director to alternate the source beam between the
reference and sample compartments.
(2) usually employ a motor drive to move the dispersive element in the monochromator.
(3) automatically correct for changes in source output with wavelength.
(4) All of the above.
i. Which of the following is true?
(1) If an analysis is accurate, it must also be precise.
(2) A precise analytical measurement will always have a small relative standard deviation.
(3) If an analysis is reproducible, it will be accurate.
(4) None of the above.
j. The presence of I 2 in a tungsten halogen source
(1) causes the source output to shift to longer wavelengths.
(2) causes the source output to shift to shorter wavelengths.
(3) increases the lifetime of the filament by preventing oxygen from reacting with the tungsten
filament.
(4) increases the lifetime of the bulb by causing vaporized tungsten to redeposit on the filament.
2. (40 points) Answer five of the following in one or two sentences:
a. When a molecule absorbs light, it increases in energy. It then returns to a lower energy state by
releasing energy. Name two forms of energy that the molecule can release.
b. Name one advantage offered by the method of standard additions over a conventional analysis
based on the construction of a calibration curve.