Download which technique or techniques would be most appropriate for use in

Sample questions Test 3
1. Circle the correct response.
a. A three electrode potentiostat is used
to apply two voltages simultaneously to the same working electrode
to measure both the current and the resistance simultaneously
to eliminate the voltage measurement error that can occur at high currents
to eliminate errors in measuring currents in solutions of low resistance
b. Measurement with an ion selective electrode is an example of
potentiometry
voltametry
conductometry
c.
coulometry
In ICP-AES the species detected is
an unexcited neutral atom,
a neutral atom or ion in an exited electronic state,
an ion in the ground state,
an atom or ion in the ground electronic state
d. Which of the following techniques has the lowest detection limits?
flame AA
flame emission
electrothermal AA
ICP AES
e. Which of the following techniques is NOT routinely used for simultaneous mutli-element analysis?
arc emission
ICP-MS
ICP-AES
AA spectroscopy
f.
In which of the following methods is the concentration of the analyte is determined from the Nernst
Equation.
potentiometry
coulometry
voltametry
conductometry
g. Which technique is most useful for determining the chemical nature of a molecule on a surface
Auger electron
XPS
X-ray
lectron
spectroscopy
fluorescence
microprobe
h. Chemical interference is not a serious problem in a plasma as compared to a flame because
a plasma has more ions than a flame
a plasma has fewer ions than a flame
a plasma is much hotter than a flame
a plasma is much cooler than a flame
i.
Mercury is commonly used as an electrode because
mercury has a high overpotential for the reduction of hydrogen ions in the solvent
mercury has a high density
mercury is the least reactive metal
mercury is easily reduced
j.
This technique is generally only used for the analysis of alkali metals
ICP-MS
differential pulse
flame emission
polarography
k. Beam (or source) modulation is used in flame AA and flame AE to
reduce the effects chemical interferences
eliminate interferences caused by emissions from the flame
eliminate ionization interferences
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flame absortion
Sample questions Test 3
increase the intensity of the source
l.
Which of the following techniques would be least useful for determining a trace amount of tin in a
sample of a metal?
x-ray
differential pulse
ICP-AES
AA
fluorescence
polarography
m. For which of the following surface techniques is it sometimes possible to detect adsorbates at part
per billion levels
XPS
SIMS
Auger
electron microprobe
n. What is detected in ICP-MS
ions in the plasma
radiation from ions in the plasma
atoms in the plasma
radiation from atoms in the plasma
o. In which of the following methods is the voltage scan preceded by a concentration phase
polarography
anodic
differential pulse
cyclic
stripping
polarography
voltametry
p. Which of the following types of probe beams can be used for high resolution surface imaging with
little surface damage
He ion
Ar ion
electron
X-ray
q. In which techniques are electrons used as a probe and X-rays are detected
x-ray fluorescence
XPS
electron microprobe
Auger
r. Which of the following is NOT a type of voltametry
(differential pulse polarography, anodic stripping, pH measurement, square wave polarography)
s. Which tecnique tends to be more sensitive to high molecular weight atoms.
XRF spectroscopy
Auger electron
ESCA
spectroscopy
t. In which of the following techniques is the sample completely destroyed ?
differential pulse
coulometry
potentiometry
polarography
SIMS
polarography
u. In which of the following electrochemical methods is the determination of concentration based on
diffusion controlled migration of analyte
conductometry
polarography
pH measurement
coulometry
v. The charging current in polarograhy is due to
undesired ions in solution,
the electrical double layer around the electrode,
concentration polarization,
overpotential
2
Sample questions Test 3
w. In which one of the following the sample is probed with X-rays and the electron emitted are
analyzed.
XPS
Auger
the electron
XRF
spectroscopy
microprobe
x. Which technique is used for simultaneous analysis and identification of multiple ions
potentiometry
coulometry
voltametry
conductometry
y. A(n) (auger, photo-, thermal, free) electron is created in a two electron process in an atom. An
upper level electron in an atom that is missing a core electron drops to a lower level to fill the hole
and simultaneously a valance electron is ejected.
z.
Which of the following techniques is not used for simultaneous multielement analysis?
flame AA
ICP-MS
ICP-AES
arc emisson
aa.
Which is FALSE about Atomic Absorption Spectroscopy?
The sensitivity for various atoms differs significantly
Hollow cathode lamps are used as sources
Flame AA has lower detection limits than electrochemical furnace AA
The energies of the transitions are in the UV-visible region
bb. Give the following two half reactions and reduction potentials, what is the spontaneous reaction and
what is the cell voltage
2+
Zn + 2e- → Zn(s) Eo = -0.763
Ni2+ + 2e- → Ni(s)
Eo = -0.250
2+
Zn + Ni(s) → Ni2+ + Zn(s) Eo = 0.513 V
Zn2+ + Ni(s) → Ni2+ + Zn(s) Eo = -0.513 V
Ni2+ + Zn(s) → Zn2+ + Ni(s) Eo = 0.513 V
Ni2+ + Zn(s) → Zn2+ + Ni(s) Eo = -0.513 V
cc. Which of the following is most useful for determining the chemical structure of an unknown
molecule ?
Auger electron spectroscopy
X-ray diffraction
electron microprobe
Atomic force microscope
dd. Which of the following is most useful for determining the atomic composition of a surface with
micrometer resolution?
X-ray flourescence
X-ray diffraction
electron microprobe
Scanning tunelling microscope
2 Briefly answer the following questions.
a.
Why is the surface concentration of an electroactive species often different from the bulk
concentration?
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Sample questions Test 3
b.
Why is ultra high vacuum needed for most surface analysis techniques.
c.
What is overpotential and what is its source?
d.
How are electrons analyzed and detected?
e.
How are X-rays analyzed and detected?
3. For each technique indicate what is measured (current, voltage, current vs. voltage, current vs. time,
etc.). Also give an example of an application of each technique.
measured
application
coulometry
differential pulse
polarography
potentiometry
4. Describe briefly how you could analyze the following samples. Indicate the instrumental technique or
techniques that you will use and what information you expect from each technique. Indicate if any
sample preparation or separation is likely to be needed. Assume that all instrumental techniques are
available to you.
a. Test for Pb in a soil sample. These are expected to be present at the ppb level.
b. Quickly determine the composition of a metal ore with a precision of 10 %.
c. Determine the Ca and Mg content of some grains.
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Sample questions Test 3
d. Determine the thickness of a thin diamond film that has been deposited on a metal surface..
e.
Test a cleaning solution for several metals and non metals simultaneously.
5 (6 ) Give a typical application for each of the following
X-ray fluorescence
XPS
SIMS
scanning tunneling microscopy
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