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KEMANA2: Analytical Chemistry 2 > Long Exam 1 > Flashcards

Long Exam 1 Flashcards

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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
Q

Light source of the AAS can be composed of

A

-hollow cathode la,p
electrodeless discharge lamp
-lasers

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26
Q

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?

A

nebulizer

specific parts:
-capillary tubing
-glass bead adjuster
-venturi
-oxidant
-glass bead
-spray chamber
-drain

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27
Q

part of the AAS that destroy analyte ions and breakdown complexes

it creates atoms (the elemental form) of the element of interest

A

Flame

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28
Q

Fuels and their corresponding oxidants for the AAS flame

A

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

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29
Q

used in electrothermal AAS that is more sensitive than a flame

this is used to introduce the sample in the AAS

A

Graphite Furnace

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30
Q

Typical fuel for electrothermal

A

Argon gas

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31
Q

purpose of matrix modifier

A

-changes the behavior of the analyte element or matrix in solution wrt temperature

-increases the volatility of the matrix

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32
Q

everything in a sample other than the analyte. it decomposes and vaporizes during the charring

A

Matrix

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33
Q

it isolates the wavelength of the maximum absorbance

A

monochromator

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34
Q

what is/are the purpose of monochrometer in the AAS?

A

-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

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35
Q

it determines the intensity of photons of the analytical line exiting the monochromator

A

detector

36
Q

types of detectors for AAS

A

-photomultiplier tubes
-solid state detector

37
Q

what are differrent types of interferences

A

-spectral interferences
-chemical interferences
-ionization interference
-matrix effect
-broadening of spectral lines

38
Q

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?

A

spectral interference

1.) do background correctiom
2.) choose different wavelength for the analysis

39
Q

a type of interference wherein any component of the sample decreases the atomization of the analyte

how to resolve this interference?

A

chemical interference

use of releasing agent to release the analyte (breaks the possible bonds with the other components)

40
Q

a type of interference wherein the ionization of analyte atoms decreases the concentration of neutral atoms

how to resolve this?

A

Ionization Interference

use of ionization suppressor (decreases the extent of ionization of analyte)

41
Q

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

A

matrix effect

42
Q

broadening of spectral lines can be caused by

A

-doppler effect
-lorentz effect
-quenching effect
-self absorption or self reversal effect

43
Q

this happens due to atoms having different components of velocity along the line of observation

A

Doppler effect

44
Q

in the doppler effect, atoms moving towards the source absorb ________ whereas atoms moving away the source absorb ______

A

lower frequency (longer wavelength), higher frequency

45
Q

result of the concentration of foreign atoms present in the environment of the emitting or absorbing atoms

A

Lorentz effect

46
Q

presence of foreign gas molecules that affects the flame/same spectral lines or resonance with the analyte

A

quenching effect

47
Q

atom emits instead of absorbing

A

self absorption/self reversal

48
Q

conversion of analyte to gas phase atoms

A

atomization

49
Q

provide sufficient energy to promote valence electrons of an atom from ground state to excited state

A

excitation

50
Q

emission

A

excited electron relaxed back to ground state giving back their energy as atomic emission

51
Q

compare/contrast AES and AAS

A

AAS
-has light source
-uses flame for atomization

AES
-no light source
-uses inductively-coupled plasma (icp) instead of flame

52
Q

compare/contrast flame and icp

A

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
Q

according to Boltzmann distribution equation, the higher distribution means that?

A

the are more population in the excited state

there will be more atoms that will emit energy

54
Q

how is icp initiated?

A

spark from a Tesla coil

55
Q

fuel for ICP

A

Argon gas

56
Q

what does the induction coil do?

A

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
Q

the production of light can be measured in what orientation?

which is more accurate?

A

1.) radial
2.)axis

radial view is much preferred because it has higher LOD and precision

58
Q

How do we analyze AES? Explain the method used.

A

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
Q

this type of analysis is used to analyze colored samples. it is also used to monitor titrations

A

UV-Vis spectrophotometer

60
Q

species that strongly absorb to UV raidiation

A

double bonds

61
Q

what is a chromophore?

A

anything that is pigmented

62
Q

give some examples of chromophore

A

-alkene
-conjugated alkene
-alkyne
-carbonyl
-carboxyl
-amido
-azo
-nitro
-nitroso
-nitrate
-aromatic

63
Q

give an example of solvent

A

n-heptane
n-hexane
ethanol
water
isooctane
dioxane

64
Q

how to conduct UV-Vis experiment?

A

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
Q

for inorganic compounds, how does absorption take place?

A

when electrons make transitions between filled and unfilled d orbitals with energies that depend on the ligands bonded to the metal ions.

66
Q

what if we want to analyze colorless samples via UV Vis?

A

we react the colorless sample to a chromophoric reagent

67
Q

it is a complex that consists of an electron donor group bonded to an electron acceptor

A

charge-transfer complex

68
Q

what happens when the charge-transfer complex after being subjected to the UV Vis spectrophotometer?

A

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
Q

Give some solvents and their LOWER wavelength limit in nm

A

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
Q

criteria for UV Vis spectrophotometry

A

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
Q

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?

A

the formation of the metal-ligand complexes produces color. the color is caused by the excitation of electrons in the d orbital

72
Q

differentiate:
spectrophotometer, spectrometer, and photometer.

A

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
Q

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

A

single beam instrument

74
Q

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

A

Double beam instrument

75
Q

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.

A

double-beam in time

76
Q

what is EM radiation?

A

emission and transmission of energy in the form of electromagnetic waves
-radiation that reacts with the analyte

77
Q

TRUE or FALSE: higher energy means higher frequency

A

TRUE. energy is directly proportional to frequency but inversely proportional to wavelength

78
Q

EM radiation that can be seen by our naked eye

A

visible light

79
Q

380-420 nm

Color absorbed?
Color observed?

A

CA: Violet
CO: Green-yellow

80
Q

420-440 nm
color absorbed?
color observed?

A

CA: Violet-blue
CO: Yellow

81
Q

440-470 nm
color absorbed?
color observed?

A

CA: Blue
CO: Orange

82
Q

recite the electromagnetic spectrum

A

.

83
Q

5 basic parts of spectrophotometer

A

light source
monochromator
cuvette
detector
digital display or meter

84
Q

Criteria for light source

A

1.) sufficient power ready for detection and measurement
2.) sufficient electromagnetic radiation
3.) constant beam with high intensity output

85
Q

characteristics of a good detector

A

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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