Final Prep Answers

Chem 155 Final review topics and questions:
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Part I. (optional) outline
================================================================
1. Statistics, mean, std deviation, propagation of error, confidence limits.
2. Sensitivity, limit of detection C MIN , limit of linearity, standard additions, internal
standards. Calculation of concentration, error in concentration, C MIN .
3. Experiment design – calibration standard and sample prep.
4. Properties of electromagnetic radiation: , , cm -1 , refractive index, diffraction,
photoelectric effect.
5. The electromagnetic spectrum – wavelengths, energies and spectroscopically
observable physical processes of interest to chemistry and physics
6. Vibrational and electronic spectroscopy
a. atoms versus molecules
b. absorbance versus fluorescence spectroscopy
c. calculation of band positions in nm, cm -1
7. Monochromators – Czerny-Turner calculations: , D -1 , EFF, R, F
8. Lasers – concepts: absorption, spontaneous emission, radiative decay,
nonradiative decay, stimulated emission, gain; operating principles of 3-level, 4-
level lasers, eximer lasers.
9. Phototube, photomultiplier tube, photodiode and CCD detectors.
a. Photoelectric detectors
i. photoelectric effect – work function, operating ranges
ii. gain equations
iii. design, relative speed, relative sensitivity
b. Semiconductor detectors
i. Materials, dopants, semiconduction, holes and electrons, PN
junctions, CCD detectors.
ii. Description of operation
iii. Design, relative speed, relative sensitivity
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Part II. outline
10. Atomic absorption spectrometry
a. Principles of FAAS – where selectivity and sensitivity arise
b. Spectrometer design
c. Atomization processes
d. Sensitvitiy and atomization: protecting agents, releasing agents, radiation
buffers
e. Bandwidth considerations and calibration curve linearity
11. Atomic emission spectrometry
f. ICP – principles
i. Ar plasma
ii. Inductive coupling
iii. torch design
g. Ar-plasmas versus flames as atomizers
h. Bandwidth considerations and noise

Chem 155 Final review topics and questions:
i. Stability considerations, matrix effects and internal standards
j. Monochromators, simultaneous multielement detection, Echelle designs
and CCD array detection
12. UV-Vis absorbance spectrometry
k. Beer’s law
l. Molecular cross sections
m. Non-Beer’s law behavior
13. FTIR
n. A interferometry
o. IR radiation and vibrational modes
p. Sampling methods: ATR, transmission mode
14. Raman
q. Dynamic polarizability
r. Virtual States
s. Stokes / Anti-stokes
t. Calculations
15. Mass spectrometry
u. Ion source
i. EI
ii. ESI
iii. CI
iv. MALDI
v. M/Z origins, isotopomers
w. Analyzer types
i. Resolution
ii. Mass range
iii. Cost
iv. Pulsed / cont.
x. Fragmentation patterns
16. Separations
y. Vocabulary
z. Principles – reverse-phase and normal-phase HPLC, separation versus
resolution
aa. VanDeempter equation
bb. Factors that determine ‘H’
cc. General elution problem / solution

Chem 155 Final review topics and questions:
=================================================================
Part I. practice problems
================================================================
The following 5 measurements of light power were made:
1000, 1010, 1015, 1008.
Calculate the mean, standard deviation, and 95% confidence interval for this
population.
1000 1010 1015 1008
4
1008.25
( 1008.25 1000) 2 ( 1008.25 1010) 2 ( 1008.25 1015) 2 ( 1008.25 1008) 2
4 1
6.2
If concentration is related to light power by the relation: C = k*P, and k = 0.0010 +/-
0.0001 and P = 9.5+/-0.2, what is the mean and standard deviation in the
concentration (Error propagation)
k 0.001 s k 0.0001 P 9.5 s P 0.2
C k P s C C
s k
k
2
s P
P
2
C 0.0095
s C 0.0010
Experimental Design
A sample of soil contains about 1 to 5 grams of arsenic per 1000 Kg
(metric ton).
a) What approximate As conc. in ppm would result from dissolving 1.00g of soil in
HF/ HNO3, filtering, and diluting to 100.0 ml
2.5 g As / 1000 Kg soil * 1 Kg soil / 1000 g soil * 1.00 g soil sample = 2.5x10 -6 g As
2.5*10 -6 g / 100 mL * 1000 mL / L * 10 6 g / g = 25 g / L => 25 ppb => 0.025 ppm
b) Your ICP instrument can measure As in the 0.01 to 10 ppm range. What would
be an appropriate range of concentrations in which to prepare standards for the
above experiment
1 – 200 ppb seems reasonable
Low std must be > 25 ppb

Chem 155 Final review topics and questions:
c) Describe how you might prepare a 0.500 ppm calibration standard from a 1000.0
ppm standard solution.
a. Pipet 1.00 mL and dilute to 100.0 mL 1000 ppm 10 ppm
b. Pipet 1.00 mL and dilute to 20.0 mL 10 ppm * 1/20 0.500 ppm
List 3 desired properties of a light detector.
a. High sensitivity
b. Low noise
c. High quantum efficiency
d. High speed
2. Sketch a photomultiplier tube and label the important parts
a. See notes
3. How many dynodes are needed for a PMT to produce at least 1,000,000
electrons per photoelectron Assume that the secondary electron yield is 4.
n
10 6 4 n ln ln 10 6 2.303log 10 6
n
( 2.3036)
ln( 4)
n 9.968 10 dynodes 4 10 1.049 10 6
4. Is it possible to detect near infrared radiation (wavelength = 1500 nm) with a
photomultiplier tube using a Na photocathode The work function of Na is 2.75
eV.
h 6.62610 34 J s c 3.0010 8 m s
h c 1eV
E
150010 9 m 1.60210 19 J
150010 9 m eV 1.60210 19 J
E 0.827eV Since E the photoelectric effect
is not promising for detection!

Chem 155 Final review topics and questions:
5. By what basic mechanism does the photodiode produce an electric current when
light strikes it
The photodiode is reverse-biased. This means that without light, no current flows. The
PN junction of the photodiode is exposed to light. When light strikes the PN junction it
may create electron-hole pairs. The bias will then sweep apart the electron-hole pairs
and convert the light into an electrical current.
6. What happens at a p-n junction when a reverse-bias is applied Draw a diagram
to support your answer. Why are photodiodes operated in reverse bias
+
+
+
+
+
-
-
-
-
The photon (red arrow) strikes the photodiode in the depletion region and an
electron-hole pair is generated. The electron and hole (red circles) are swept
apart by an electric field. In reverse bias, the diode produces zero current in the
dark. Low or zero dark current is a good quality in a photo-detector.
7. What is the maximum gain of a photodiode transducer Is this better than a
phototube
Photodiode max gain = 1 = equal to the phototube max gain.

Chem 155 Final review topics and questions:
8. Draw a diagram of the photosensitive element in a charge-coupled-device array
detector and illustrate what happens when light strikes this detector.
- 1 0 V
- 1 0 V
- 1 0 V
A l c o n t a c t
S i O 2
n - S i
-
-
- -
-
-
-
- + - +
-
-
- -
- -
-
1. e- are repelled
from Al contact
2. h strikes
depletion region
3. h+ accumulate at
Al contact – charge
stored here is a
measure of light!
9. Draw a simple diagram placing the following elements in the proper order for (A)
an absorbance spectrometer and (B) a fluorescence spectrometer.
Detector
Source
Signal Processor
Wavelength Selector
Sample Holder
A
source Sample holder Wavelength sel detector Signal processor
B
source
10. How are light power for sample and blank and sample concentration related to
analyte concentration in (A) fluorescence and (B) absorbance spectrometry
A fluor: P = C*k
Wavelength sel detector Signal processor
Sample holder
The only difference is that the signal is collected
at right angles to source beam!
B abs: P = P0 x10-A
11. Give an example of a material that is transparent in (A) the UV-Visible and Near
IR, and (B) the IR regions of the EM spectrum.

Chem 155 Final review topics and questions:
A silica – SiO 2 (other acceptable: sapphire, calcium fluoride)
B zinc selenide – ZnSe (also germanium, silicon and potassium bromide)
12. Give an example of a light source that is operative in (A) the UV-Visible and Near
IR, and (B) the IR regions of the EM spectrum. For each, give an example of a
line source and a continuum source.
A
UV, VIS or NIR line source hollow cathode lamp or laser
UV, VIS or NIR continuum source tungsten halogen or Xe-arc lamp
B
- IR continuum source Nernst glower
13. Draw a simple schematic of a laser and label the important parts.
14. What processes are involved in loss and gain in a laser light cavity. Name them
and give a short equation showing photons and states to indicate your answer.
15. Draw an energy level diagram for a 4-level laser and indicate the levels involved
in the lasing transition.
16. What must be the case if laser radiation transiting the laser cavity is to be
amplified by stimulated emission rather than attenuated

Chem 155 Final review topics and questions:
17. Why is a 4-level laser more easily pumped than a 3-level one
18. Draw an energy level diagram for an eximer laser. Indicate what molecules and
what electronic states are involved in each level.
19. Draw a diagram of a classical light wave and label the axes (you may ignore
magnetic fields). On this wave identify the wavelength and amplitude.

Chem 155 Final review topics and questions:
20. Fill in the table to indicate what happens when HeNe laser radiation (wavelength
= 632.8 nm) passes from air (n = 1) into glass (n = 1.6).
Wavelength / nm Frequency /
Air 632.8 4.74E14 1.96
Glass 395.5 4.74E14 1.96
s -1
Energy / eV
c
c
3.0010 8 m s
632.810 9 m
4.741 10 14 Hz
632.8
1.6
395.5
E
h
h c
6.62610 34 J s 3.0010 8 m s
632.810 9 m
6.2410 18 eV J
1.96eV
21. How much light is reflected at normal incidence
2 1.6 1 1.0 2 1
2 1
2
100% 5.3%

Energy / eV
Chem 155 Final review topics and questions:
22. Light of variable wavelength is incident on a piece of metal in vacuum, the metal
is held at zero volts. Electrons emitted from the metal are collected and analyzed
as a function of energy. Draw a diagram of the photoelectron energy versus the
irradiating light frequency. Identify the x-intercept and the slope of the curve and
indicate the significance of both.
See notes on photoelectric effect: x-intercept is the work function of the metal –
the energy required to take an electron out of the conduction band and into
vacuum. The slope of the line is Plank’s constant.
23. A small hypothetical molecule has the following energy level diagram. Indicate,
using arrows, the transitions corresponding to infrared light absorption, visible
light absorption, and visible light fluorescence. Be prepared to sketch the
absorbance or fluorescence spectra as well.
3
2
1
Vis
abs.
Vis
fluor.
Vis
abs.
Vis
fluor.
0
IR
abs.
400 500 600
Wavelength / nm increasing

Path of analyte through plasma or flame
Chem 155 Final review topics and questions:
================================================================
Part II Practice problems:
================================================================
1. Fill in the empty boxes consistent with the diagram. SEE NOTES
In boxes 1 to 6 inddicate in what form the
analyte is likely to exist:
6
In boxes 7 and 8 below put the
equation that relates concentration
and light power corresponding to
emission (7) and absorption (8):
5
Emission
7
HCL
h
4
Absorption
8
3
2
1
Nebulize
Liquds
Solids
Gases

Chem 155 Final review topics and questions:
2. Compare Ar-plasma and air-C 2 H 2 flames in the following categories:
Quality
circle correct
Electron Ar-plasma has higher lower equal air-C 2 H 2 flame.
density
e - density than
Temperature Ar-plasma is higher lower equal air-C 2 H 2 flame.
temperature than
Chemical Ar-plasma has higher lower equal air-C 2 H 2 flame.
reactivity
reactivity than
Formation of Ar-plasma is higher lower equal air-C 2 H 2 flame.
oxides
likelihood than
Atomization
efficiency
Ar-plasma is superior inferior
equal to
air-C 2 H 2 flame.
3. Compare inductively coupled plasma atomic emission spectrometry (ICP-AES) to
flame atomic absorption spectroscopy (FAAS) in the following categories:
Quality
circle correct
choice
Cost to buy / ICP-AES is higher, lower, FAAS
operate
equal cost than
Simultaneous ICP-AES is more, less, FAAS
Multielement
detection
equally
competent than
Dynamic Range ICP-AES has larger, smaller, FAAS
equal dynamic
range than
Detection Limit ICP-AES has higher, lower,
equal detection
limits than
FAAS
4. Because of the mulit-element capability and atomization / temperature sensitivity
of emission intensity, the following analytical method has proved highly
successful in ICP-AES:
a. Standard addidions c. D2 background correction
b. Internal standards d. nonlinear calibration analysis
5. Formation of oxides or molecular species in flame/plasma can be suppressed by:
c. EDTA or other complexing agents
d. Addition of KCl to the matrix
e. Addition of oxyanions such as sulfate or phosphate.
f. Standard additions methods.
6. Ionization of analyte atoms in flame/plasma can be suppressed by:
g. EDTA or other complexing agents
h. Addition of KCl to the matrix
i. Addition of oxyanions such as sulfate or phosphate.
j. Internal standards methods.

Chem 155 Final review topics and questions:
7. Fill in the following table:
Absorbance P Po %T C / M
0.00 1 1.00 100 0.0000
0.30 0.5 1.00 50 0.0003
1.00 0.1 1.00 10 0.001
2.00 0.01 1.00 1 0.002
3.00 0.001 1.00 0.1 0.003
A log %T
100
10 A %T
100
%T 100 10 A
100 10 0.3 50 100 10 1 10 100 10 2 1 100 10 3 0.1
%T 100 P P0
P
%T
100 P0
8. Based on this, comment on the relative reliability (i.e. accuracy or precision) of
absorbance measurements at A=1 and A=3.
A=1 is good, A=3 means light power P is 1/1000 of blank - too small of a light
power signal to work with

Chem 155 Final review topics and questions:
9. Define the following:
a. Mobile phase
b. Stationary phase
c. General elution problem
Changing to conditions that are strong enough to elute strongly retained
components will fail to resolve weakly retained ones and conditions that are weak
enough to resolve weakly retained components will fail to elute strongly retained
components. Solution is GRADIENT ELUTION: to change elution conditions
during chromatographic run: begin with weakly eluting conditions and ramp to
strongly eluting ones. In many cases this will give adequate time to separate
weakly retained species, but will elute strongly retained ones before too much
broadening or time has passed

Chem 155 Final review topics and questions:
10. Identify 5 processes that lead to band broadening in HPLC and describe them.
Van Deemter terms can be used, plus injection zone size and column
overloading.
a. Eddy diffusion / multipath term
b. Longitudinal diffusion
c. Resistance to mass transfer
d. Injection zone width
e. Column overloading
11. Identify the strong and weak mobile phase modifiers:
Identify as strong, weak or not used.
Name
Stationary Water Methanol Hexane
Phase
Reverse-phase Oil -
weak strong Not used
octadecane
Normal-phase Bare silica Not used strong weak
12. A 1.000 cm cuvette filled with water (blank) was paced in a spectrophotometer
set to 640 nm. The detector signal was 1509 A.. With a sample of 1.06x10 -5 M
sample of magnesium phthalocyanine (MgPC) the detector signal read 1312 A.
What is the molar extinction coefficient of MgPC
A b C log
P
P0
P
log
P0
b C
log 1312
1509
5.732 10 3
1 1.0610 5
13. Why are internal standards used in the GCMS experiment
d. To compensate for injection variability.

Chem 155 Final review topics and questions:
14. What is the function of the reagent blank in the metals experiment
To evaluate analyte levels in the Blank.
15. What is the function of the spike recovery analysis in the metals experiment
To validate the sample preparation step.
16. Why are the absorption and emission maxima offset for the fluorophore
rhodamine 6G
Absorbance is electronic plus vibrational energy change but
Emission is electronic minus vibrational energy change.
Abs.
Em.
Em. arrows
are shorter.
17. Why are ABC samples run without solvent to measure their FTIR specta
Samples are measured “neat” because the solvent would absorb the IR radiation.
18. Why is a cuvette not used to measure the FTIR spectra
Typical IR chromophore has ε 100-1000 M -1 cm -1 , and neat, C may be 1-10 M.
A = εC = 100 minimum.
T=10 -A = 0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001
No light would get through…

Chem 155 Final review topics and questions:
19. Circle the correct answer. In comparison to double-beam scanning
spectrophotometers, diode array spectrophotometers are:
Quality
Spectrometer Type
Diode Array Double Beam
more accurate absorbance
x
more accurate wavelength
x
much faster
x
higher resolution
x
more complex
x
more expensive
x
20. What is the IR selection rule
Dipole moment must change during vibration.
21. What is the Raman selection rule
Polarizability must change during vibration.
22. Sketch the normal modes of vibration of the water molecule and indicate the
Raman and IR activity:
Mode Sketch IR Active Raman Active
Symmetric stretch
O
Yes Yes
H
O
Antisymmetric
Yes
No
Stretch
H H
O
Bend Yes Yes
H
H
H
23. The frequency of the Raman Stokes line for 488.0 nm laser light scattering from
a 1500 cm -1 CO stretching vibrational mode.
v Laser
10 7 nm
cm
488.0nm
v Laser 20492cm 1 v Vibration 1500cm 1
v Raman v Laser v Vibration v Raman 18992cm 1 Stokes Line
v Raman v Laser v Vibration v Raman 21992cm 1 Anti-Stokes Line

Chem 155 Final review topics and questions:
24. Elaborate the following acronyms:
e. ATR – Attenuated Total Reflection
f. FTIR – Fourier Transform Infrared
25. Which will be observed at a higher frequency the OH stretch in ethanol or the
OD stretch in deuterated ethanol
k
OH Because H is lighter than D and v where k = bond force constant and µ
= reduced mass of oscillator.
26. In an FTIR, high resolution corresponds to:
g. Long interferometer drive
h. High beam intensity
i. High absorbance
j. High mirror velocity
k. Double-beam optics
27. Fill in the following to indicate the transitions involved in Stokes and anti-Stokes
Raman scattering:
S1
So

Chem 155 Final review topics and questions:
28. Fill in the following table:
Mass analyzer Resolution
(high or low)
Input:
Continuous / pulsed
Cost
(high or low)
Quadrupole Low Continuous Low
Double-focusing
High Pulsed High
electric / magnetic
sector.
Time of flight. High Pulsed High
29. Fill in the following table:
Ionization Source Fragmentation
(high or low)
Electron Impact
High
(EI)
Mode:
Continuous / pulsed
Cont.
Chemical ionization
(CI)
Matrix Assisted
Laser Desoprtion
Ionization (MALDI)
Electrospray
Ionization (ESI)
Low
Low
Low
Cont.
Pulsed
Cont.

Signal
Chem 155 Final review topics and questions:
30. Label the arrows:
Factors that determine performance in chromatography:
a
b
c
d
0 5 10 15 20 25 30
Ret ention T ime / s
Improve resolution a Retention Time c Band width d
Improve efficiency a Determined by K P –
partition coefficient
Improve selectivity b Achieved by change of
mobile phase
Achieved by change of
stationary phase
c
b
b
Set by MP velocity and
SP quality
Set by longitudinal
diffusion
Set by resistance to
mass transfer
Set by variable flow path
d
d
d
d