Ch 22 Bulk Electrolysis: Electrogravimetry and Coulometry

Question 1

The two bulk electroanalytical methods

Answer 1

electrogravimetry, and
coulometry

Question 2

In the bulk electroanalytical methods __________ is present

Answer 2

Current

Question 3

Two additional phenomena, ____________, must be considered when current is present.

Answer 3

IR drop and polarization

Question 4

is the rate of charge flow in
a circuit or solution. One ampere of
current is a charge flow rate of one
coulomb per second

Answer 4

Current

Question 5

, the electrical potential
difference, is the potential energy that
results from the separation of charges.

Answer 5

Voltage

Question 6

Ohm’s law:

Answer 6

E = IR, or I = E/R.

Question 7

Ohmic Potential is the product of the resistance R of a cell in ohms (V) and the current I in amperes (A). Also called

Answer 7

IR Drop

Question 8

is current that is
always in one direction, that is, unidirectional.

Answer 8

Direct current (dc)

Question 9

The direction of____________ reverses periodically.

Answer 9

alternating
current (ac)

Question 10

to minimize the IR drop in the cell by having a very small cell resistance (high ionic strength) _____is used

Answer 10

three-electrode cell

Question 11

is the deviation of the
electrode potential from its theoretical
Nernst equation value on the passage
of current.

Answer 11

Polarization

Question 12

is the potential difference between the theoretical
cell potential from Equation 22-2 and
the actual cell potential at a given level
of current.

Answer 12

Overvoltage

Question 13

is the movement of
material, such as ions, from one
location to another

Answer 13

Mass transfer

Question 14

Polarization phenomena can be divided into two categories:

Answer 14

concentration polarization and kinetic polarization.

Question 15

occurs because of the finite rate of mass transfer from
the solution to the electrode surface

Answer 15

Concentration polarization

Question 16

is the movement of a species
under the influence of a concentration
gradient. It is the process that causes
ions or molecules to move from a more
concentrated part of a solution to a
more dilute

Answer 16

Diffusion

Question 17

Reactants are transported to the surface of an electrode by three mechanisms:

Answer 17

diffusion, migration, and convection

Question 18

is the movement of ions
through a solution as a result of
electrostatic attraction between the
electrodes and the ions.

Answer 18

Migration

Question 19

the rate of diffusion and the current become correspondingly larger until the
surface concentration falls to zero, and the maximum or __________ is reached

Answer 19

limiting current

Question 20

Migration of analyte species can be
minimized by having a high concentration of an inert electrolyte, called a _____ present in the cell.

Answer 20

supporting
electrolyte,

Question 21

is the transport of
ions or molecules through a solution
as a result of stirring, vibration, or
temperature gradients.

Answer 21

Convection

Question 22

such as stirring or agitation, tends to decrease the thickness of the diffusion layer at the surface of an electrode and thus decrease concentration
polarization

Answer 22

Forced convection,

Question 23

resulting from temperature or density differences also
contributes to the transport of molecules and ions to and from an electrode.

Answer 23

. Natural convection

Question 24

The current in a kinetically
polarized cell is governed by the
rate of electron transfer rather
than the rate of mass transfer.

Answer 24

kinetic polarization

Question 25

is the current per unit surface area of the electrode (A/cm2).

Answer 25

Current density

Question 26

is most commonly encountered when the reactant or product in an electrochemical cell is gas

Answer 26

Kinetic polarization

Question 27

the only practical way of achieving separation of species whose electrode potentials differ by a few tenths of a volt is to measure the cathode potential continuously against a reference electrode whose potential is known. The applied cell potential can then be adjusted to maintain the cathode potential at the desired level. An analysis performed in this way is called a

Answer 27

controlled-potential electrolysis.

Question 28

the method where potential of the working electrode is maintained at a constant level versus a reference electrode, such as a SCE.

Answer 28

potentiostatic method,

Question 29

is the electrode at which the analytical reaction occurs.

Answer 29

working electrode

Question 29

The voltage applied to the cell is controlled by the variable

Answer 29

resistor, R.

Question 30

A ____ is a species that is easily reduced (or oxidized). It helps maintain the potential of the working electrode at a relatively small constant value and prevents reactions that would occur under more reducing or oxidizing conditions.

Answer 30

depolarizer

Question 31

A ________- maintains the working electrode potential at a constant value relative to a reference electrode.

Answer 31

potentiostat

Question 32

is particularly useful for removing easily reduced elements such as copper, nickel, cobalt, silver, and cadmium are separated at this electrode

Answer 32

mercury cathode

Question 33

is a potent tool for separating and determining metallic species having standard potentials that differ by only a few tenths of a volt.

Answer 33

Controlled-potential electrolysis

Question 34

is the amount of charge required to produce 0.00111800 g of silver metal from silver ions.

Answer 34

coulomb (C)

Question 35

The charge on an electron (and proton) is defined as .

Answer 35

1.6022 x 10^19 coulombs (C)

Question 36

A rate of charge flow equal to one coulomb per second

Answer 36

one ampere (A) of current

Question 37

Two methods often called the coulometric titrimetry

Answer 37

controlled-potential (potentiostatic) coulometry & controlled-current coulometry

Question 38

is also called coulometric titrimetry.

Answer 38

Constant-current coulometry

Question 39

One equivalent of chemical change is the change brought about by

Answer 39

1 mol of electrons

Question 40

The two working electrode of Electrolysis cells for potentiostatic coulometry.

Answer 40

(a) platinum-gauze, (b) mercury-pool

Question 41

Coulometric titrations are performed with a constant-current source, sometimes called a

Answer 41

galvanostat

Question 42

Constant-current generators are sometimes called .

Answer 42

galvanostats

Question 43

Detecting the End Point in Coulometric titrations,

Answer 43

Potentiometric or amperometric end points are used in Karl Fischer titrators

Question 44

The constant-current source for a coulometric titration is an electronic device capable of maintaining a current of

Answer 44

200 mA

Question 45

Applications of Coulometric Titrations

Answer 45

Neutralization Titrations Precipitation and Complex-Formation Reactions Oxidation/Reduction Titrations

Question 46

Applications of coulometric titrations

Answer 46

Neutralization titration Precipitation and complex -formation reactions Oxidation/reduction titration