Ch 22 Bulk Electrolysis: Electrogravimetry and Coulometry Flashcards

1
Q

The two bulk electroanalytical methods

A

electrogravimetry, and
coulometry

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2
Q

In the bulk electroanalytical methods __________ is present

A

Current

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3
Q

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

A

IR drop and polarization

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4
Q

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

A

Current

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5
Q

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

A

Voltage

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6
Q

Ohm’s law:

A

E = IR, or I = E/R.

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7
Q

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

A

IR Drop

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8
Q

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

A

Direct current (dc)

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9
Q

The direction of____________ reverses periodically.

A

alternating
current (ac)

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10
Q

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

A

three-electrode cell

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11
Q

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

A

Polarization

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12
Q

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

A

Overvoltage

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13
Q

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

A

Mass transfer

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14
Q

Polarization phenomena can be divided into two categories:

A

concentration polarization and kinetic polarization.

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15
Q

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

A

Concentration polarization

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16
Q

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

A

Diffusion

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17
Q

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

A

diffusion, migration, and convection

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18
Q

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

A

Migration

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19
Q

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

A

limiting current

20
Q

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

A

supporting
electrolyte,

21
Q

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

A

Convection

22
Q

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

A

Forced convection,

23
Q

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

A

. Natural convection

24
Q

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

A

kinetic polarization

25
is the current per unit surface area of the electrode (A/cm2).
Current density
26
is most commonly encountered when the reactant or product in an electrochemical cell is gas
Kinetic polarization
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
controlled-potential electrolysis.
28
the method where potential of the working electrode is maintained at a constant level versus a reference electrode, such as a SCE.
potentiostatic method,
29
is the electrode at which the analytical reaction occurs.
working electrode
29
The voltage applied to the cell is controlled by the variable
resistor, R.
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.
depolarizer
31
A ________- maintains the working electrode potential at a constant value relative to a reference electrode.
potentiostat
32
is particularly useful for removing easily reduced elements such as copper, nickel, cobalt, silver, and cadmium are separated at this electrode
mercury cathode
33
is a potent tool for separating and determining metallic species having standard potentials that differ by only a few tenths of a volt.
Controlled-potential electrolysis
34
is the amount of charge required to produce 0.00111800 g of silver metal from silver ions.
coulomb (C)
35
The charge on an electron (and proton) is defined as .
1.6022 x 10^19 coulombs (C)
36
A rate of charge flow equal to one coulomb per second
one ampere (A) of current
37
Two methods often called the coulometric titrimetry
controlled-potential (potentiostatic) coulometry & controlled-current coulometry
38
is also called coulometric titrimetry.
Constant-current coulometry
39
One equivalent of chemical change is the change brought about by
1 mol of electrons
40
The two working electrode of Electrolysis cells for potentiostatic coulometry.
(a) platinum-gauze, (b) mercury-pool
41
Coulometric titrations are performed with a constant-current source, sometimes called a
galvanostat
42
Constant-current generators are sometimes called .
galvanostats
43
Detecting the End Point in Coulometric titrations,
Potentiometric or amperometric end points are used in Karl Fischer titrators
44
The constant-current source for a coulometric titration is an electronic device capable of maintaining a current of
200 mA
45
Applications of Coulometric Titrations
Neutralization Titrations Precipitation and Complex-Formation Reactions Oxidation/Reduction Titrations
46
Applications of coulometric titrations
Neutralization titration Precipitation and complex -formation reactions Oxidation/reduction titration