CHEM 322 – study questions for test 1
Fill in the blank.
a) If the absorbance of a 0.020 M sample is 0.150 in a 2.0 cm cell, what is the absorbance of a
0.010 M sample of the same type in a 1.0 cm cell? _______________
b) By what factor is the signal-to-noise ratio improved if 1000 spectra are averaged _____.
c) At a particular wavelength, a solution that is 0.010 M in A has an absorbance of 0.26 and a
solution that is 0.10 M in B has an absorbance of 0.16. What is the absorbance of a solution
that is 0.010 M in A and 0.10 M in B? ______________
e) If a spectrophotometer reads 92% T with the blank and 53% T with the sample, what is the
absorbance of the sample? ________
f) Two emission lines occur at 772.0 and 772.8 nm. Determine how many lines a grating must
have to resolve these emission lines in second order. ________
f. For a particular determination, the slope of the calibration curve was 0.153 L/mg. The
standard deviation of the noise level for a blank sample was measured to be 0.022. What is the
detection limit in concentration units for this technique?
g. Sketch a typical single beam UV spectrometer. Label the various parts and show the light
path. Use the back of this page if you need more room
h. Sketch the 19F NMR spectrum for 31P19F31H2. Assume that JPF = 6 Hz. and JHF =2 Hz.
i. What are the principal advantages and disadvantages of Fourier Transform Spectroscopy?
j. What would allow you to distinguish the 1H NMR spectrum of CH3CH2OH from
CH3CH2OCH3?
k. What are the advantages of a double beam instrument as compared to a single beam
instrument?
l. Briefly discuss Beer's Law. What is it and why does it sometimes fail?
m. How many spectra must be averaged to increase the signal to noise ratio by a factor of 5.
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