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Flashcards in Test 3 Deck (88):
1

galvanic cell

produces electrical energy

2

electrolytic cell

consumes electrical energy

3

when positive solution is applied to electode, layers of solution adjacent to electrode acquire ? charge

negative

4

In cell notation, the anode is on the ? side

left

5

=-nFE

dG

6

nonlinear data in plot of potential versus current is indicative of ?

electrode polarization

7

ideal polarized electrode

current remains constant and independent of potential over wide range

8

ideal nonpolarized electrode

potential remains constant and independent of current over wide range

9

potentiometry

measuring potential of cell without drawing appreciable current

10

typical potentiometer cell in cell notation

ref !! analyte soln ! indicator electrode

11

reference electrode in potentiometry

half cell of accurately known potential that is independent of concentration of analyte or other ions in solution

12

indicator electrode in potentiometry

immersed in solution and develops a potential based on activity of the analyte

13

Potential measure of cell

difference between reference and indicator, add junction potential

14

Two common reference electrodes

Calomel and silver-silver chloride

15

calomel contents

Hg in contact with solution saturated with mercury chloride and known concentration of KCl

16

potential of calomel

.244 V

17

advantage of calomel electrode

easy preparation

18

disadvantage of calomel

large temperature coefficient, slow to reach equilibrium when temperature is changed. can only be used at low temperature.

19

when potential of electrode is lowered

reduction of analyte occurs. electron adds to LUMO

20

when potential of electrode is increased

oxidation of analyte occurs. electron leaves HOMO

21

no current passes through ? electrode

reference electrode

22

Ag-AgCl voltage

.222 V

23

advantage of Ag-AgCl electrode

can be used at temps above 60C

24

disadvantage of Ag-Ag-Cl electrode

silver ions react with more sample components than Hg

25

at low pH, potential Eb is positive/negative. external barrier poternatial is higher /lower

positive, higher

26

alkaline errors

as pH increases, error increases. lower reading than actual

27

asymmetric error fixed using?

calibration

28

glass membrane composition

SiO2 > Na2O > CaO. Each Si bound to four O. Singly charged cations are mobile in lattice and are responsible for conduction and balancing negatively charged SiO4-.

29

mechanism of CO2 snsing by gas probe

CO2 effues through gas permeable membrane and glass membrane. Combines with water to change pH. measured by internal glass calomel electrode.

30

L for metallic electrodes

standard electrode potential

31

L for membrane electrodes

sum of many constants

32

Voltammetry

measure current in EChem cell w/ polarization conditions

33

reference electrode in voltammetry

used in maintaining potential at WE

34

farradaic

movement of electrons across electrode due to redox species in solution

35

nonfarradaic

movement of charged species due to charge buildup on electrode surface

36

mass transfer

movement of species due to chemical or electrical gradient

37

migration

influencing movement due to charge

38

diffusion

influencing movement due to chemical gradient

39

convection

influencing movement due to agitation

40

flux

sum of migration, diffusion and convection

41

migration eliminated by ?

diluting with inert supporting electrolytes. inert electrolyte does the migrating instead of analyte

42

convection resolved with ?>

rotating disk or motionless electrode

43

fick's first law

chemical species diffuses down concentration gradient

44

peak current increases/decreases with scan rate. Why?

increases. stronger concentration gradient, more rapid diffusion

45

? bind to Au

alkyl thiols

46

1st gen glucose biosensor

glucose diffuses through outer membrane into immobilized glucose oxidase that catalyzes formation of H2O2 from oxygen. H2O2 diffuses through inner membrane and dissociates releasing two electrons. electrons current genrated is proportional to glucose concentration.

47

2nd gen glucose biosensor

glucose oxidase transfers electrons to a mediator instead of O2.

48

benefit of 2nd gen glucose biosensor

can oxidize mediator at low potential, lowering interference

49

common mediators

ferrocene derivatives, organic conducting salts

50

Cell response to glucose meter implantation in subcutaneous tissue

leukocytes generate fibrous capsule around meter. causes inflammation

51

electrochemical DNA hybridization detection method

modify Au electrode with thiolated ssDNA. expose to complement. Expose viologen probe that binds to DNA and produces EC signal.

52

viologen

multiply cationic dimer. forms radical when reduced. overlap of singly occupied pi* orbitals

53

xenobiotic induced carcinogens

metabolism process tries to eliminate using cyt p450. generates reactive metabolites what can damage dna

54

genotoxicity

looks for straight dna damage

55

ames assay

use bacteria to see whether a chemical reaction can cause cancer. gives yes/no answer

56

problems with detection of dna damaging chemicals

interspecies metabolism differences. fixed by using human enzymes

57

site specific dna damage

carcinogens adduct at specific locations

58

dna damage studies

electrode modified with dna oligomer containing known hotspot sequence. expose carcinogen for timed period. monitor voltammetry as function of BPDE exposure.

59

CV fit and isotherm. frumpkin curve fit.

integrate waves in plot of potential vs current. find how much dna on electrode.

60

voltammetry pulse method plot

staircase in plot of time vs potential

61

benefits of pulse methods

better signal to noise ratio

62

when is current measured in pulse methods

when difference between the desired faradaic curve and the interfering charge is large

63

as pXc increases, Ecell ?

decreases

64

pulse voltammetry curve decays with

negative square root of time

65

more sensitive pulse method

square wave

66

? determines speed of scan in square wave

frequency

67

? determines potential step in square wave

amplitude

68

how is square wave plotted

plot difference of forward and reverse curent

69

chomatography equilibrium constant

Kc=[Cs]/[Cm]

70

retention factor doesn't depend on ?

geometry or flow rate

71

retention factor formula

Ka=[ta-tm]/[tm]

72

? retention factors go through column quickly

low

73

selectivity factor

ratio of elution rate between two species

74

Want high/low plate number

high

75

want high/low plate height

low

76

relationship between plate number and height

L=N*H where L is column length

77

van deemter plots

flow rate vs plate height

78

LC vs GC. lower flow rates

LC

79

LC vs GC. lower heights

LC

80

LC vs GC. lower plate number

LC

81

LC vs GC. superior in terms of separation efficiency.

GC

82

van deemter eqn

H=A + B/U +CsU + CmU

83

eddy diffusion

enhanced with higher flow rates, increases plate height

84

linear diffusion decreased by ?

higher flow rate, lowers plate height

85

parameters of packed columns

particle diameter

86

parameters of open column

diameter of tube

87

good resolution value

1.5

88

by convention, the reference electrode is on the ? in cell notation

left