Ch 23 Voltammetry

Question 1

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 1

voltammetry

Question 2

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

Answer 2

amperometry

Question 3

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

Answer 3

Voltammetric methods

Question 4

is voltammetry in that the working electrode is the unique dropping mercury electrode.

Answer 4

Polarography

Question 5

What are the most common excitation signals used in voltammetry

Answer 5

linear scan
differential pulse
square wave
triangular

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.

Answer 6

supporting electrolyte

Question 7

is the electrode at which the analyte is oxidized
or reduced.

Answer 7

working electrode

Question 8

is often a coil of platinum wire or a pool of mercury.

Answer 8

counter electrode(CE)

Question 9

The cell is made up of three electrodes immersed
in a solution containing the analyte namely

Answer 9

Supporting electrode
Working electrode
Counter electrode

Question 10

many metal ions are reversibly reduced to
amalgams at the surface of a _______ electrode, which can be used in Large negative potentials

Answer 10

mercury electrode

Question 11

Metals which are soluble in
mercury form liquid alloys
known as

Answer 11

amalgams

Question 12

working electrodes
with surface areas smaller than a few
square millimeters were called

Answer 12

microelectrodes

Question 13

micrometer-sized
electrodes were sometimes called

Answer 13

ultramicroelectrodes

Question 14

is an ∫-shaped ( sigmoidal shape)
wave that appears in current-voltage
plots in voltammetry

Answer 14

voltammetric wave

Question 15

is the current plateau that is observed
at the top of the voltammetric wave.

Answer 15

limiting current

Question 16

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

Answer 16

half-wave potential

Question 17

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

Answer 17

Hydrodynamic voltammetry

Question 18

during an electrolysis, reactant is carried to the surface of an electrode by three mechanisms:

Answer 18

migration
convection
diffusion

Question 19

during an electrolysis, reactant is carried to the surface of an electrode under the influence of an electric field,

Answer 19

Migration

Question 20

during an electrolysis, reactant is carried to the surface of an electrode resulting from stirring or vibration,

Answer 20

Convection

Question 21

during an electrolysis, reactant is carried to the surface of an electrode due to concentration differences between the film of liquid at the electrode surface and the bulk of the solution.

Answer 21

diffusion

Question 22

What is the formula of the potential between the working electrode and the reference electrode (Eappl)

Answer 22

Eappl = E0 - 0.0592/ n log cP/cA - Eref

Question 23

Formula of current

Answer 23

i = nFAD (‘c/ ‘x)

Question 24

liquid flow patterns as an effect of stirring that occurs at low flow velocities and has smooth and regular motion,

Answer 24

Laminar flow

Question 25

liquid flow patterns as an effect of stirring that happens at high velocities and has irregular, fluctuating motion

Answer 25

Turbulent flow

Question 26

What is the Flow patterns and regions of interest near the working electrode in hydrodynamic voltammetry.

Answer 26

Nernst diffusion layer of stagnant solution > Laminar flow region > Turbulent flow region

Question 27

a stagnant layer where the concentrations of reactant and product vary as a function of distance from the electrode surface and that there are concentration gradients

Answer 27

Nernst diffusion layer

Question 28

Region where the convection maintains the concentration of A at its original value and the concentration of P at a very small level.

Answer 28

turbulent and laminar flow regions

Question 29

Thickness of Nerst Diffusion layer

Answer 29

ranges from 10^-2 to 10^-3 cm, depending on the efficiency of the stirring and the viscosity of the liquid.

Question 30

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

Answer 30

half-wave potential

Question 31

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

Answer 31

totally irreversible system

Question 32

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

Answer 32

partially reversible system

Question 33

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 33

Sparging

Question 34

The most important uses of hydrodynamic voltammetry include

Answer 34

(1) detection and determination of chemical species as they exit from chromatographic columns or flow-injection apparatus; (2) routine determination of oxygen and certain species of biochemical interest, such as glucose, lactose, and sucrose; (3) detection of end points in coulometric and volumetric titrations; and (4) fundamental studies of electrochemical processes.

Question 35

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 35

Hydrodynamic voltammetry

Question 36

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 36

Oxygen Sensors. 

Question 37

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

Answer 37

Clark oxygen sensor

Question 38

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

Answer 38

Enzyme-based sensors

Question 39

A plot of current versus the angular velocity of the disk in radians per second (ω^1/2) is known as a _________, and deviations from the linear relationship often indicate kinetic limitations on the electron transfer process.

Answer 39

Levich plot

Question 40

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

Answer 40

pseudopolarography

Question 41

was the first type of voltammetry to be discovered and used. It is essentially no convection or migration, and a dropping mercury electrode (DME) is used as the working electrode.

Answer 41

Linear-scan polarography

Question 42

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

Answer 42

residual current

Question 43

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 43

Diffusion current

Question 44

The diffusion current is ___________ to analyte concentration in the bulk of solution

Answer 44

directly proportional

Question 45

Two sources of residual current

Answer 45

1. the reduction of trace impurities 2. charging, or capacitive

Question 45

is the current that results from an oxidation/reduction process.

Answer 45

faradaic current

Question 45

is a charging current that results because the mercury drop is expanding and must be charged to the electrode potential. Does not accompanied by oxidation/reduction process.

Answer 45

nonfaradaic current

Question 45

electrons are repelled from the surface toward the bulk of mercury, and a negative current is the result. The mercury surface is uncharged, and the charging current is zero. This potential is called the

Answer 45

potential of zero charge

Question 45

The direction of the initial scan may be either negative, as shown, or positive, depending on the composition of the sample. A scan in the direction of more positive potentials /opposite direction is called a

Answer 45

reverse scan

Question 46

The voltage extrema at which reversal takes place are called

Answer 46

switching potential

Question 46

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

Answer 46

cyclic voltammetry (CV),

Question 46

The direction of the initial scan may be either negative, as shown, or positive, depending on the composition of the sample. A scan in the direction of more negative potentials is termed a

Answer 46

forward scan,

Question 47

two most important pulse techniques

Answer 47

differential-pulse voltammetry square-wave voltammetry

Question 48

detection limits with differential-pulse voltammetry are two to three orders of magnitude lower than those for classical voltammetry and lie in the range of

Answer 48

10^-7 to 10^-8 M.

Question 49

is a type of pulse voltammetry that offers the advantage of great speed and high sensitivity. An entire voltammogram is obtained in less than 10 ms, which has been used with hanging mercury drop electrodes and with other electrodes

Answer 49

Square-wave voltammetry

Question 50

The following organic functional groups produce voltammetric waves:

Answer 50

1. Carbonyl groups 2. Certain carboxylic acids 3. Most peroxides and epoxides 4. Nitro, nitroso, amine oxide, and azo groups 5. Most organic halogen groups 6. Carbon/carbon double bonds 7. Hydroquinones and mercaptans.

Question 51

the analyte is deposited by reduction and then analyzed by oxidation from the small volume mercury film or drop. 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 51

In anodic stripping methods

Question 52

the analyte is electrolyzed into a small volume of mercury by oxidation and then stripped by reduction. The working electrode behaves as an anode during the deposition step and as a cathode during stripping

Answer 52

In cathodic stripping methods,

Question 53

The dimensions of this electrodes are typically smaller than about 20 mm and may be as small as a 30 nm in diameter and 2 mm in length. The electrochemical behavior of these tiny electrodes is significantly different from classical electrodes and appears to offer advantages in certain analytical applications. Such electrodes are often called

Answer 53

microscopic electrodes, or microelectrodes

Question 54

The current in a cell containing a dropping mercury electrode undergoes periodic fluctuations corresponding in frequency to the drop rate

Answer 54

Polarographic currents

Question 55

The following organic functional groups produce voltametric waves

Answer 55

Carbonyl groups Carboxylic acids Peroxide and epoxide Nitro nitroso amine oxide and azo groups Organic halogen groups Carbon carbon double bonds Hydroquinones and mercaptans