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

Sample questions Test 3-KEY
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
voltametry
conductometry
potentiometry
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.
coulometry
voltametry
conductometry
potentiometry
g. Which technique is most useful for determining the chemical nature of a molecule on a surface
Auger electron
X-ray
electron
XPS
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 absorption
Sample questions Test 3-KEY
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?
differential pulse
ICP-AES
AA
x-ray
polarography
fluorescence
m. For which of the following surface techniques is it sometimes possible to detect adsorbates at part
per billion levels
XPS
Auger
electron microprobe
SIMS
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
differential pulse
cyclic
anodic
polarography
voltametry
stripping
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
X-ray
electron
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 technique 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
potentiometry
coulometry
polarography
SIMS
polarography
u. In which of the following electrochemical methods is the determination of concentration based on
diffusion controlled migration of analyte?
conductometry
pH measurement
coulometry
polarography
v. The charging current in polarograhy is due to
undesired ions in solution
the electrical double layer around the electrode
concentration polarization
overpotential
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Sample questions Test 3-KEY
w. In which one of the following the sample is probed with X-rays and the electron emitted are
analyzed.
Auger
the electron
XRF
XPS
spectroscopy
microprobe
x. Which technique is used for simultaneous analysis and identification of multiple ions
potentiometry
coulometry
conductometry
voltametry
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?
ICP-MS
ICP-AES
arc emisson
flame AA
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-KEY
The electrochemical processes occur at the surface of the electrodes and the
concentration near the electrode can be greater than less than the bulk
concentration since it take time for diffusion to equalize the concentration.
b.
Why is ultra high vacuum needed for most surface analysis techniques.
Ultrahigh vacuum is needed to help keep the surface clean and to prevent ions
and electrons from reacting with other molecules.
c.
What is overpotential and what is its source?
Overpotential refers to the extra voltage needed, beyond that predicted by
thermodynamics, to cause an oxidation or reduction to occur. It arises from the
activation energy of process. Overpotential is minimized at low current.
d.
How are electrons analyzed and detected?
The energy of an electron can be measured with an electrostatic analyzer. The
electron signal is detected and amplified by an electron multiplier which functions like a
photomultiplier.
e.
How are X-rays analyzed and detected?
X-Rays are detected by the ionization that they cause. In vacuum tube designs
the X-rays ionize a low pressure gas and these ions are detected. The X-ray energy can
be analyzed with an X-ray monochrometer that uses a salt crystal in place of a grating.
In solid state X-ray detectors, the X-rays create ions within the substrate and in this case
the current pulses produced can be analyzed by height to directly determine the energy
without a monochromator.
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.
coulometry
differential pulse
polarography
potentiometry
measured
current vs time (charge)
current vs voltage
voltage
application
titrations
multielement analysis for
metals. Many organics
can also be analyzed.
pH measurement, ion
selective electrodes
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.
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Sample questions Test 3-KEY
techniques - anodic stripping, electrothermal AA, or ICP-MS. In each case, the
sample would first have to be dissolved into an aqueous solution. For anodic
stripping an electrolyte would have to be added.
b. Quickly determine the composition of a metal ore with a precision of 10 %.
X-ray fluorescence (XRF) - no sample prep.
c. Determine the Ca and Mg content of some grains.
AA, AE, or ICP, The sample would have to dissolved in an aqueous solution
d. Determine the thickness of a thin diamond film that has been deposited on a metal surface..
SIMS or Auger with depth profiling. No preparation
e.
Test a cleaning solution for several metals and non metals simultaneously.
ICP-AES or ICP-MS. No preparation
5 (6 ) Give a typical application for each of the following
X-ray fluorescence - determination of elemental composition a pigments on a painting,
determination of the major components of an ore. Nondestructive elemental analysis
in air.
XPS - determination of elemental composition of a metal or semiconductor surface.
Must be done in UHV.
SIMS - atomic or molecular analysis of a surface. Depth profiling is also possible
scanning tunneling microscopy - determination of surface topography with atomic resolution
scanning electron microscope - determination of surface topography with resolution better
than optical microscopes
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