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KEMANA2: Analytical Chemistry 2 > Long Exam 1 > Flashcards

Long Exam 1 Flashcards

(85 cards)

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1
Q

Process involving the emission of light from any substance in the excited states

A

fluorescence

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2
Q

What is a flurophore

A

any type of material that fluoresces

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3
Q

what are the two types of fluorophore

A

1.) endogenous — naturally occurring (amino acids such as tryptophan, tyrosine, phenylalanine)

2.) exogenous — synthesized such as organic dyes or fluorescent tags (fluorescein)

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4
Q

what is a fluorescein?

A

it acts like a chromophoric reagent and used to be attached on compounds that do not fluoresce

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5
Q

TRUE OR FALSE: Not all compounds fluoresce

A

False. All compounds fluoresce but not all are evident because some only have insignificant amounts of fluorescing components.

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6
Q

TRUE OR FALSE: Fluorescence is an emission energy

A

TRUE

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7
Q

TRUE OR FALSE: fluorophore can absorb/emit light

A

TRUE

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8
Q

explain the Jablonski energy diagram

A

.

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9
Q

duration of excitation (absorption)

A

10^-16 seconds

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10
Q

duration of internal conversion and vibrational relaxation

A

10^-14 to 10^-11

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11
Q

duration of fluorescence

A

10^-9 to 10^7 sec

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12
Q

what is excited triplet state

A
  • also called as forbidden state
    -slightly lower than the excited state
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13
Q

compounds that are most likely to fluoresce

A

-containing aromatic rings (most intense and most useful for molecular fluorescence emission)

-some aliphatic and alicyclic compounds

  • compounds that are highly conjugated
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14
Q

equation of fluorescence spectroscopy and define the parameters

A

F = 2.303K Io ebc
F = fluorescence intensity
K = constant based on instrument geometry
Io = intensity of the excitation light
a = fluorophore’s molar absorptivity
b = pathlength
c = concentration

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15
Q

differentiate different types of spectroscopy

A

absorption (UV-Vis, AAS)
-linear (source to wavelength selector)
-has light source

emission (AES)
-linear
-no light source

emission (fluorescence)
-90 degree angle (source-sample-wavelength selector)
-has light source

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16
Q

give some light source/lamps for fluorescence spectrometer

A

Mercury arc lamp (366, 405, 436, 546, 578 nm)

Xenon arc lamp ( 250-1000 nm)

Tungsten-halogen lamp (350-1000 nm)

Blue diode laser/LED (4xx nm)

Helium-cadmium laser (325, 442 nm)

Argon ion laser (457, 488, 514 nm)

YAG Laser (532 nm

Helium-neon laser (633 nm)

Yellow diode laser/LED (5XX nm)

Krypton ion laser (568, 647 nm)

Red diode laser (6xx nm)

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17
Q

what are some metals that can be analyzed via AAS?

A

Alkali Metals (Li, Na, K, Rb, Cs)
Alkaline Earth Metals (Be, Mg, Ca, Sr, Ba)
Sc, Y, Ti, Zr, V, Nb, Ta, Cr, Mb, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg
Triels (B, Al, Ga, In, Tl)
Tetrels (Si, Ge, Sn, Pb)
Pnictogens (As, Sb, Bi)
Chalcogen (As, Sb, Bi)

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18
Q

Can nonmetals be analyzed using AAS?

A

Yes. As long as atoms can be converted into gas phase

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19
Q

differentiate the atomic absorption techniques

A

1.) Flame Atomic Absorption (FAAS)
-air (oxidizer)
-acetylene (fuel)
-samples in the form of LIQUID ONLY
-2360 up to 2600K
-you need enough amount of sample

2.) Electrothermal AAS
-no more flame
-you can place your sample in a an electrically graphite tube
-consistent temp profile
-up to 3000K
-better accuracy
-requires less sample
-LOD to 100 ppb
- samples can be in the form of solution, slurries, solid samples

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20
Q

best analyzed by AES only

elements

A

Na, K, Rb, Sr, Co, Th, Eu, P, S

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21
Q

Requires N2O/C2H2 flame. Better analyzed by inductively coupled plasma (ICP) only

elements

A

Ba, Sc, Ti, V, Zr, Nb, Mo, Si, Ge, Hf, Ta, W, Os, Ir, Nd, Dy, Ho, Er

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22
Q

can be analyzed via both ICP and AES

elements

A

Ba, Pr, Y, La, U, Sm, Gd, Tb, B, Al

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23
Q

Enumerate the components of the AAS

A

Light source
Flame
Nebulizer
Monochromator
Detector
Computer

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24
Q

part of the AAS that provides analytical light for the element of interest and provides constant and intense beam

A

Light Source

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25
Light source of the AAS can be composed of
-hollow cathode la,p electrodeless discharge lamp -lasers
26
part of the AAS that aspirates liquid aerosol at control rate, forms fine aerosol, and mix aerosol, fuel, and oxidant what are its specific parts?
nebulizer specific parts: -capillary tubing -glass bead adjuster -venturi -oxidant -glass bead -spray chamber -drain
27
part of the AAS that destroy analyte ions and breakdown complexes it creates atoms (the elemental form) of the element of interest
Flame
28
Fuels and their corresponding oxidants for the AAS flame
Fuel: Acetylene Oxidant: Air Temp: 2400 to 2700 K Fuel: Acetylene Oxidant: Nitrous oxide Temp:2900-3100 K Fuel: Acetylene Oxidant: Oxygen Temp: 3300-3400 Fuel: Hydrogen Oxidant: Air Temp: 2300-2400 Fuel: Hydrogen Oxidant:Oxygen Temp: 2800-3000 Fuel: Cyanogen Oxidant: Oxygen Temp: 4800 K
29
used in electrothermal AAS that is more sensitive than a flame this is used to introduce the sample in the AAS
Graphite Furnace
30
Typical fuel for electrothermal
Argon gas
31
purpose of matrix modifier
-changes the behavior of the analyte element or matrix in solution wrt temperature -increases the volatility of the matrix
32
everything in a sample other than the analyte. it decomposes and vaporizes during the charring
Matrix
33
it isolates the wavelength of the maximum absorbance
monochromator
34
what is/are the purpose of monochrometer in the AAS?
-isolate analytical lines’ photons passing through the flame -remove scattered light of other wavelengths from the flame so that only a narrow spectral line impinges on the photomultiplier tubes -allows only light not absorbed by sample to reach the pm tubes
35
it determines the intensity of photons of the analytical line exiting the monochromator
detector
36
types of detectors for AAS
-photomultiplier tubes -solid state detector
37
what are differrent types of interferences
-spectral interferences -chemical interferences -ionization interference -matrix effect -broadening of spectral lines
38
it is the type of interference where there is an overlap of the analyte signal with signals due to other elements or molecules in the sample or with signals due to the flame or furnace how can we resolve this type of interference?
spectral interference 1.) do background correctiom 2.) choose different wavelength for the analysis
39
a type of interference wherein any component of the sample decreases the atomization of the analyte how to resolve this interference?
chemical interference use of releasing agent to release the analyte (breaks the possible bonds with the other components)
40
a type of interference wherein the ionization of analyte atoms decreases the concentration of neutral atoms how to resolve this?
Ionization Interference use of ionization suppressor (decreases the extent of ionization of analyte)
41
a type of interference where it can either suppress or enhance the absorbance signal of the analyte. it occurs when components of sample matrix other than the analyte react to form molecular species and sample background
matrix effect
42
broadening of spectral lines can be caused by
-doppler effect -lorentz effect -quenching effect -self absorption or self reversal effect
43
this happens due to atoms having different components of velocity along the line of observation
Doppler effect
44
in the doppler effect, atoms moving towards the source absorb ________ whereas atoms moving away the source absorb ______
lower frequency (longer wavelength), higher frequency
45
result of the concentration of foreign atoms present in the environment of the emitting or absorbing atoms
Lorentz effect
46
presence of foreign gas molecules that affects the flame/same spectral lines or resonance with the analyte
quenching effect
47
atom emits instead of absorbing
self absorption/self reversal
48
conversion of analyte to gas phase atoms
atomization
49
provide sufficient energy to promote valence electrons of an atom from ground state to excited state
excitation
50
emission
excited electron relaxed back to ground state giving back their energy as atomic emission
51
compare/contrast AES and AAS
AAS -has light source -uses flame for atomization AES -no light source -uses inductively-coupled plasma (icp) instead of flame
52
compare/contrast flame and icp
FLAME Temp: 1700-3150 K Spectroscopy: AAS/AES Boltzmann Distribution: 8.75 x 10e-4 ICP Temp: 4000-6000K Spectroscopy: ICP-AES, ICP-MS Boltzmann Distribution: 512 x 10e-4
53
according to Boltzmann distribution equation, the higher distribution means that?
the are more population in the excited state there will be more atoms that will emit energy
54
how is icp initiated?
spark from a Tesla coil
55
fuel for ICP
Argon gas
56
what does the induction coil do?
creates an alternating radio frequency and create a fluctuating magnetic field that induces the argon ions and the analyte to move in a circular path
57
the production of light can be measured in what orientation? which is more accurate?
1.) radial 2.)axis radial view is much preferred because it has higher LOD and precision
58
How do we analyze AES? Explain the method used.
Standard Addition method -we prepare a standard -dilute them to obtain at least 5 standards with different known concentrations -we measure their absorbances -we get the x-intercept. that is the concentration of the sample without any of the standards.
59
this type of analysis is used to analyze colored samples. it is also used to monitor titrations
UV-Vis spectrophotometer
60
species that strongly absorb to UV raidiation
double bonds
61
what is a chromophore?
anything that is pigmented
62
give some examples of chromophore
-alkene -conjugated alkene -alkyne -carbonyl -carboxyl -amido -azo -nitro -nitroso -nitrate -aromatic
63
give an example of solvent
n-heptane n-hexane ethanol water isooctane dioxane
64
how to conduct UV-Vis experiment?
1.) wavelength scan - we determine the maximum wavelength 2.)set the instrument at the maximum wavelength and determine the absorbance of the prepared samples with different concentrations but run the blank first
65
for inorganic compounds, how does absorption take place?
when electrons make transitions between filled and unfilled d orbitals with energies that depend on the ligands bonded to the metal ions.
66
what if we want to analyze colorless samples via UV Vis?
we react the colorless sample to a chromophoric reagent
67
it is a complex that consists of an electron donor group bonded to an electron acceptor
charge-transfer complex
68
what happens when the charge-transfer complex after being subjected to the UV Vis spectrophotometer?
the electron from the donor is transferred to an orbital that is associated with the acceptor the excited state is thus the product o a kind of redox process
69
Give some solvents and their LOWER wavelength limit in nm
water - 180 nm ethanol - 220 nm hexane - 200 nm cyclohexane 200 nm carbon tetrachloride - 260 nm diethyl ether - 210 nm cetone - 330 nm dioxane - 320 nm cellosolve - 320 nm
70
criteria for UV Vis spectrophotometry
1.) sample solutions must be diluted 2.) the solvent must be transparent in the region of the spectrum where the sample absorbs 3.)the analyte must be sufficiently soluble in the solvent
71
some metals do not absorb/absorb at lower wavelengths which makes the analysis impossible/difficult. however, if they are reacted to species such as diethyldithiocarbamate and diphenylthiocarbazobne, analysis via UV Vis spectrophotometer is possible. how is this so?
the formation of the metal-ligand complexes produces color. the color is caused by the excitation of electrons in the d orbital
72
differentiate: spectrophotometer, spectrometer, and photometer.
1.) spectrophotometer - kind of spectrometer -gets the ratio of the radiant powers of two beams -has monochromator for wavelength selection 2.)spectrometer - converts electrical intensities into electrical signals -uses monochromator or polyhromator 3.) photometer - uses a filter for wavelength selection -much simpler
73
a type of UV Vis spectrophotometer where radiation from the filter passes through either the reference or sample cell before striking the photodetector -this type of UV Vis spectrophotometer is where you add your sample and your black — taking it out and taking it back every after analysis
single beam instrument
74
a type of UV Vis instrument where radiation from the filter split into two beams that simultaneously pass through reference and sample cells before striking 2 matched photodetectors -you don’t have to remove and return your sample and your solvent. -gets the ratio of the absorbance of the sample and the solvent -has two photodetectors
Double beam instrument
75
a type of instrument where the beam is alternately sent through reference and sample cells, striking a single photodetector. a period of only a few milliseconds separates the beams as they pass through the two cells.
double-beam in time
76
what is EM radiation?
emission and transmission of energy in the form of electromagnetic waves -radiation that reacts with the analyte
77
TRUE or FALSE: higher energy means higher frequency
TRUE. energy is directly proportional to frequency but inversely proportional to wavelength
78
EM radiation that can be seen by our naked eye
visible light
79
380-420 nm Color absorbed? Color observed?
CA: Violet CO: Green-yellow
80
420-440 nm color absorbed? color observed?
CA: Violet-blue CO: Yellow
81
440-470 nm color absorbed? color observed?
CA: Blue CO: Orange
82
recite the electromagnetic spectrum
.
83
5 basic parts of spectrophotometer
light source monochromator cuvette detector digital display or meter
84
Criteria for light source
1.) sufficient power ready for detection and measurement 2.) sufficient electromagnetic radiation 3.) constant beam with high intensity output
85
characteristics of a good detector
1.) high sensitivity 2.) high signal to noise ratio 3.) constant response over a considerable range of wavelengths 4.) fast response time 5.) minimal output signal in the absence of illumination

KEMANA2: Analytical Chemistry 2 (2 decks)

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