Chapter 21: Voltammetry

Question 1

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

Answer 1

amperometry

Question 2

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.

Answer 2

voltammetry

Question 3

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

Answer 3

TRUE

Question 4

is voltammetry at the dropping mercury electrode

Answer 4

polarogrpahy

Question 5

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

Answer 5

voltammetric methods

Question 6

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.

Answer 6

supporting electrolyte

Question 7

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

Answer 7

working electrode

Question 8

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

Answer 8

reference electrode

Question 9

Electrolysis current passes between
the working electrode and a

Answer 9

counter electrode

Question 10

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

Answer 10

working electrode

Question 11

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

Answer 11

mercury working electrodes

Question 12

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

Answer 12

hanging mercury drop electrode (HMDE)

Question 13

Metals that are soluble in mercury form liquid alloys known as

Answer 13

amalgams

Question 14

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

Answer 14

microelectrodes

Question 15

micrometer-sized electrodes were sometimes called

Answer 15

ultramicroelectrodes

Question 16

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

Answer 16

voltammograms

Question 17

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

Answer 17

voltammetric wave

Question 18

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

Answer 18

limiting current

Question 19

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

Answer 19

half-wave potental, E1/2

Question 20

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

Answer 20

hydrodynamic voltammetry

Question 21

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

Answer 21

half-wave potentials

Question 22

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

Answer 22

Reproducible limiting currents

Question 23

Mass-transport processes include

Answer 23

diffusion
migration
convection

Question 24

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

Answer 24

laminar flow

Question 25

happens at high velocities and has irregular, fluctuating motion,

Answer 25

turbulent flow

Question 26

two types of flow depending on the average flow velocity

Answer 26

laminar flow turbulent flow

Question 27

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

Answer 27

half-wave potential

Question 28

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

Answer 28

totally irreversible system

Question 29

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

Answer 29

partially reversible system

Question 30

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.

Answer 30

sparging

Question 31

forst step of amperometric procedures

Answer 31

removal of oxygen it interferes in determining other species

Question 32

complete voltammetric cells and are better referred to as

Answer 32

sensors

Question 33

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.

Answer 33

oxygen sensors

Question 34

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

Answer 34

clark oxygen sensors

Question 35

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

Answer 35

TRUE

Question 36

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.

Answer 36

hydrodyamic electrode

Question 37

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

Answer 37

rotating ring-disk electrode

Question 38

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

Answer 38

pseudopolarography

Question 39

Polarographic currents are controlled by

Answer 39

diffusion only not convection

Question 40

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

Answer 40

linear scan polarography

Question 41

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

Answer 41

residual current

Question 42

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

Answer 42

diffusion current

Question 43

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

Answer 43

TRUE

Question 44

polarographic limiting currents are usually termed

Answer 44

diffusion currents id

Question 45

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

Answer 45

faradaic current

Question 46

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

Answer 46

nonfaradaic current

Question 47

two sources of current

Answer 47

reduction of trace impurities charging/ capacitive/ current

Question 48

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

Answer 48

cyclic voltammetry

Question 49

The voltage extrema at which reversal takes place are called

Answer 49

switching potentials

Question 50

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

Answer 50

forward scan reverse scan

Question 51

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

Answer 51

pulse voltammetry

Question 52

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

Answer 52

derivative voltammograms

Question 53

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

Answer 53

square wave voltammetry

Question 54

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

Answer 54

TRUE

Question 55

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.

Answer 55

anodic stripping methods

Question 56

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

Answer 56

cathodic stripping method

Question 57

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

Answer 57

TRUE

Question 58

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

Answer 58

voltammetric methods

Question 59

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

Answer 59

TRUE

Question 60

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

Answer 60

potentiometric measurements

Question 61

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

Answer 61

working electrode reference electrode counter electrode supporting electrolyte

Question 62

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

Answer 62

counter electrode

Question 63

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

Answer 63

positive potential limitations

Question 64

arise from the reduction of water to produce hydrogen

Answer 64

negtaive limits

Question 65

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)

Answer 65

sandwich type microelectrode

Question 66

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.

Answer 66

dropping mercury electrode (DME)

Question 67

important uses of hydrodynamic voltammetry

Answer 67

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

Question 68

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

Answer 68

hydrodynamic voltammetry

Question 69

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

Answer 69

enzyme-based sensors

Question 70

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

Answer 70

enzyme based

Question 71

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

Answer 71

voltammetric sensors potentiometric pH electrode