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ANALYTICAL CHEMISTRY C3 > Chapter 21: Voltammetry > Flashcards

Chapter 21: Voltammetry Flashcards

1
Q

When the current is proportional to analyte concentration is monitored at a fixed potential,

A

amperometry

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2
Q

refers to a group of electroanalytical methods in which we acquire information about the analyte by measuring current in an electrochemical cell as a function of applied potential.

A

voltammetry

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3
Q

TRUE or FALSE
coulometry, measures are taken to minimize or compensate for the effects of concentration polarization. Furthermore, in voltammetry, there is minimal consumption of analyte, but in coulometry essentially all the analyte is converted to another state

A

TRUE

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4
Q

is voltammetry at the dropping mercury electrode

A

polarogrpahy

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5
Q

are based on measuring current as a function
of the potential applied to a small electrode.

A

voltammetric methods

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6
Q

is a salt added in excess to the analyte
solution. Most commonly, it is
an alkali metal salt that does not
react at the working electrode at
the potentials being used. The salt
reduces the effects of migration and
lowers the resistance of the solution.

A

supporting electrolyte

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7
Q

is the electrode at which the analyte is
oxidized or reduced and whose potential versus a reference electrode is varied linearly with time

A

working electrode

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8
Q

The potential between the working electrode and
the __________is controlled, which _____ has a potential that remains constant throughout the experiment

A

reference electrode

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9
Q

Electrolysis current passes between
the working electrode and a

A

counter electrode

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10
Q

take a variety of shapes and forms.
Often, they are small flat disks of a conductor that are press fitted into a rod of an inert material, such as Teflon or Kel-F that has imbedded in it a wire contact

A

working electrode

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11
Q

have been widely used in voltammetry for several reasons. One is the relatively large negative potential range and many metal ions are reversibly reduced to amalgams at the surface of a mercury electrode, simplifying the chemistry

A

mercury working electrodes

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12
Q

The simplest is a MERCURY FILM ELECTRODE formed by electrodeposition of the metal onto a disk electrode

A

hanging mercury drop electrode (HMDE)

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13
Q

Metals that are soluble in mercury form liquid alloys known as

A

amalgams

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14
Q

Historically, working electrodes with surface areas smaller than a few square millimeters were called _________. Such electrodes consist of small diameter metal wires or fibers (5 to 100 mm) sealed within tempered glass bodies. The flattened end of the microelectrode is polished to a mirror finish, which can be maintained using alumina and/or diamond polish

A

microelectrodes

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15
Q

micrometer-sized electrodes were sometimes called

A

ultramicroelectrodes

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16
Q

are plotted with positive current in the top hemisphere and negative currents in the bottom

A

voltammograms

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17
Q

is an ∫-shaped wave that appears in current-voltage plots in voltammetry.

A

voltammetric wave

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18
Q

The_____________ in voltammetry is the current plateau that is observed at the top of the voltammetric wave. It occurs because the surface
concentration of the analyte falls to zero. At this point, the mass transfer rate is its maximum value

A

limiting current

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19
Q

occurs when the current is equal to one half
of the limiting value.

A

half-wave potental, E1/2

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20
Q

is a type of voltammetry in which the
analyte solution is kept in continuous
motion

A

hydrodynamic voltammetry

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21
Q

are sometimes useful for identification
of the components of a solution.

A

half-wave potentials

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22
Q

can be achieved rapidly when either the analyte
solution or the working electrode is in continuous and reproducible motion

A

Reproducible limiting currents

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23
Q

Mass-transport processes include

A

diffusion
migration
convection

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24
Q

occurs at low flow velocities and has smooth and regular motion,

A

laminar flow

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25
Q

happens at high
velocities and has irregular, fluctuating motion,

A

turbulent flow

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26
Q

two types of flow depending on the average flow velocity

A

laminar flow
turbulent flow

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27
Q

is an identifier for the redox couple and is closely related to the standard reduction potential.

A

half-wave potential

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28
Q

In a ___________, either the forward or the
reverse reaction is so slow as to be completely negligible.

A

totally irreversible system

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29
Q

In a _______, the reaction in
one direction is much slower than
the other, although not totally
insignificant.

A

partially reversible system

30
Q

is a process in which dissolved gases are swept out of a solvent by bubbling an inert gas, such as nitrogen, argon, or helium, through the solution.

A

sparging

31
Q

forst step of amperometric procedures

A

removal of oxygen

it interferes in determining other species

32
Q

complete voltammetric cells and are better referred to as

A

sensors

33
Q

What sensor refers to the determination of dissolved oxygen in a variety of aqueous environments, such as seawater, blood, sewage, effluents from chemical plants, and soils, is of tremendous importance to industry, biomedical and environmental research, and clinical medicine.

A

oxygen sensors

34
Q

is widely used in clinical laboratories for the
determination of dissolved O2 in blood and other body fluids

A

clark oxygen sensors

35
Q

TRUE or FALSE
Voltammetric sensors are used for H2O2 and O2, while a potentiometric pH electrode is used for H1.

A

TRUE

36
Q

can be used to estimate the equivalence point of titrations if at least one of the participants or products of the reaction involved is oxidized
or reduced at a working electrode.

A

hydrodyamic electrode

37
Q

is a modified rotating disk electrode that is useful
for studying electrode reactions; it has little use in analysis

A

rotating ring-disk electrode

38
Q

RDE detection with a mercury film electrode is sometimes referred to as

A

pseudopolarography

39
Q

Polarographic currents are controlled by

A

diffusion only not convection

40
Q

was the first type of voltammetry to be discovered and used. It differs from hydrodynamic voltammetry in two significant way
1. no convection or migration
2. dropping mercury electrode

A

linear scan polarography

41
Q

The _______ in polarography is the small current
observed in the absence of an electroactive species

A

residual current

42
Q

is the limiting current observed in polarography
when the current is limited only by the rate of diffusion to the dropping mercury electrode surface.

A

diffusion current

43
Q

TRUE or FALSE
The diffusion current in polarography is proportional to the concentration of analyte.

A

TRUE

44
Q

polarographic limiting currents are usually termed

A

diffusion currents id

45
Q

The ____________ in an electrochemical cell is the current that results from an oxidation/
reduction process

A

faradaic current

46
Q

is a charging current that results because the mercury drop is expanding and must be charged to the electrode potential

A

nonfaradaic current

47
Q

two sources of current

A

reduction of trace impurities
charging/ capacitive/ current

48
Q

the current response of a small stationary electrode in an unstirred solution is excited by a triangular voltage waveform

A

cyclic voltammetry

49
Q

The voltage extrema at which reversal takes place are called

A

switching potentials

50
Q

a scan in the direction of more negative potentials is termed a __________, while one in the opposite direction is called a _________

A

forward scan
reverse scan

51
Q

is an electroanalytical technique used to study the electrochemical behavior of species in solution

A

pulse voltammetry

52
Q

yield peaks that are convenient for qualitative identification of analytes based on the peak
potential, Epeak

A

derivative voltammograms

53
Q

is a type of pulse voltammetry that offers the advantage of great speed and high sensitivity.

A

square wave voltammetry

54
Q

TRUE or FALSE
Pulse methods have largely replaced classical voltammetry because of their greater sensitivity, convenience, and selectivity

A

TRUE

55
Q

the working electrode behaves as a cathode during the deposition step and as an anode during the stripping step, with the analyte being
oxidized back to its original form.

A

anodic stripping methods

56
Q

the working electrode behaves as an anode during the deposition step and as a cathode during stripping.

A

cathodic stripping method

57
Q

TRUE or FALSE
A major advantage of stripping analysis is the
capability for electrochemically preconcentrating the analyte prior to the measurement step.

A

TRUE

58
Q

are based on measuring current as a function
of the potential applied to a small electrode.

A

voltammetric methods

59
Q

TRUE or FALSE
In voltammetry, the current that develops in an electrochemical cell is measured under
conditions of complete concentration polarization

A

TRUE

60
Q

are made at currents that approach zero and where polarization is absent

A

potentiometric measurements

61
Q

voltammetry comprises three electrodes such as ________ and a nonreactive electrolyte called ______

A

working electrode
reference electrode
counter electrode
supporting electrolyte

62
Q

is often a coil of platinum wire or a pool of mercury, which electrolysis current passes between the working electrode and this electrode

A

counter electrode

63
Q

are caused by large currents hat develo due to oxidation of the water to give molecular oxygen

A

positive potential limitations

64
Q

arise from the reduction of water to produce hydrogen

A

negtaive limits

65
Q

commercially available ______________for voltammetry (or amperometry) in flowing streams. The block is made of polyether (ether ketone) (PEEK) and is available in several formats with different size electrodes (3 mm and 6 mm; see the blue area in the center of the figure) and various arrays (dual 3 mm and quad 2 mm)

A

sandwich type microelectrode

66
Q

is used in nearly all early polarographic experiments. It consists of roughly 10 cm of a
fine capillary tubing (inside diameter 5 0.05 mm) through which mercury is forced
by a mercury head of perhaps 50 cm.

A

dropping mercury electrode (DME)

67
Q

important uses of hydrodynamic voltammetry

A
  1. detection and determination of chemical species as they exit in chromatographic columns
  2. routine determination of oxygen and certain species of biochemical interest
  3. detection of end points in coulometric and volumetric titrations
  4. fundamental studies of electrochemical processes
68
Q

is widely used for detection and determination of oxidizable or reducible compounds or ions that have been separated by liquid chromatography
or that are produced by flow-injection methods

A

hydrodynamic voltammetry

69
Q

what sensor refers to a membrane in this case is more complex and consists of three layers. The outer layer is a polycarbonate film that is permeable to glucose but impermeable to proteins and other constituents of blood. The middle layer is an immobilized enzyme; glucose oxidase in this example. The inner layer is a cellulose acetate membrane, which is permeable
to small molecules, such as hydrogen peroxide

A

enzyme-based sensors

70
Q

sensors can be
based on detecting hydrogen
peroxide, oxygen, or H1,
depending on the analyte and
enzyme

A

enzyme based

71
Q

____ are used for H2O2 and O2, while
a _______________ is used for H+.

A

voltammetric sensors
potentiometric pH electrode

ANALYTICAL CHEMISTRY C3 (21 decks)

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