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

Chemistry 325 Instrumental Analysis February 3, 1995
1. (40 points) Circle the correct answer for each of the following:
a. Photomultiplier tubes are not useful as infrared detectors because
(1) Infrared photons do not carry enough energy to eject photoelectrons from the photocathode.
(2) Infrared sources are too intense and cause degradation of the photocathode.
(3) Infrared sources output a light beam that is too large in diameter to be compatible with the
photomultiplier tube.
(4) None of the above.
b. In an experiment based on Beer's Law,
(1) Increasing the sample pathlength will increase the transmittance.
(2) Increasing absorptivity will increase the transmittance.
(3) Decreasing concentration will decrease the transmittance.
(4) Increasing the sample pathlength will increase the absorbance.
c. A photon whose wavelength is 510 nm is
(1) a visible photon
(2) an ultraviolet photon
(3) an infrared photon
(4) a microwave photon
d. Which of the following is false?
(1) Visible photons carry more energy than infrared photons.
(2) Microwave photons carry more energy than infrared photons.
(3) Ultraviolet photons carry more energy than visible photons.
(4) X-ray photons carry more energy than microwave photons.
e. The calculation (0.203 + 0.139) / 2.766 should be reported as
(1) 0.1236
(2) 0.123
(3) 0.124
(4) 0.12
f. Given the grating equation, it can be seen that
(1) the distance between the grooves of a diffraction grating has no effect on its performance.
(2) the angle of incidence of photons striking a diffraction grating must be held constant if the
grating is to function properly.
(3) the angle at which a photon reflects from the grating is unique for each wavelength.
(4) None of the above.