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ANALYTICAL CHEMISTRY C3 > Bulk Electrolysis: Electrogravimetry and Coulometry > Flashcards

Bulk Electrolysis: Electrogravimetry and Coulometry Flashcards

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1
Q

are related methods that are based on electrolysis carried out long enough to ensure complete oxidation or reduction of the analyte to a product of known composition.

A

electrogravimetry and coulometry

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2
Q

is to determine the amount of analyte present by converting it to a product that is weighed as a deposit on one of the electrodes

A

electrogravimetry

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3
Q

determine the amount of analyte by measuring the quantity of electrical charge needed for complete conversion to a product

A

coulometry

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4
Q

two additional phenomena that must be considered when current is present, which because of these phenomena, potentials larger than the thermodynamic potential are needed to operate an electrolytic cell

A

IR drop and polarization

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5
Q

also known as the IR drop, which describes the effect of this resistance on the magnitude of the current in the cell

A

Ohmic potential

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6
Q

The product of the resistance R of a cell in ohms 1V2 and the current I in amperes (A) is
called the

A

ohmic potential or IR drop

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7
Q

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

A

direct current

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8
Q

is the rate of charge flow in a circuit or solution

A

current

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9
Q

direction always reverses unidirectionally, ac

A

alternating current

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10
Q

Usually try to minimize the IR drop in the cell by having a very small cell resistance (high ionic strength) or by using a special

A

three-electrode cell

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11
Q

is the departure/ 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 and the actual cell potential at a given level of current

A

overvoltage

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13
Q

Cells that exhibit nonlinear behavior at higher currents exhibit polarization, and the degree of polarization is given by an __________. it also refers to the potential difference between the theoretical cell potential and the actual cell potential at a given level of current

A

overvoltage or overpotential

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14
Q

is an electrode phenomenon that may affect either or both of the electrodes in a cell.

A

polarization

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15
Q

polarization phenomena can be divided into two categories

A

concentration polarization and kinetic polarization

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16
Q

occurs because of the finite rate of mass transfer from the solution to the electrode surface, which electron transfer between a reactive species in a solution and an electrode can take place only from the interfacial region located at the adjacent to the surface of the electrode

A

concentration polarization

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17
Q

occurs when reactant species do not arrive at the surface of the electrode or product species do not leave the surface of the electrode fast
enough to maintain the desired current.

A

concentration polarization

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18
Q

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

A

diffusion
migration
convection

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19
Q

When there is a concentration difference between two regions of a solution, ions or molecules move from the more concentrated region to the more dilute.

A

diffusion

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20
Q

TRUE or FALSE
The rate of diffusion is directly proportional to the concentration difference.

A

TRUE

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21
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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22
Q

The electrostatic process by which ions move under the influence of an electric field is called ___________. primarily, this process causes the mass transfer in the bulk of the solution in a cell.

A

migration

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23
Q

migration of analyte species can be minimized by having a high concentration of an inert electrode called a

A

supporting electrolyte

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24
Q

It refers to the transport of ions or molecules through a solution as a result of stirring, vibration, or temperature gradients, which reactants can also be transferred to or from an electrode by mechanical means.

A

convection

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25
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

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26
Q

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

A

natural convection

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27
Q

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

A

convection

28
Q

the magnitude of the current is limited by the rate of one or both of the electrode reactions, that is, the rate of electron transfer between the reactants and the electrodes

A

kinetic polarization

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

29
Q

is most pronounced for electrode processes that yield gaseous products because the kinetics of the gas evolution process are complicated and often slow and can be negligible for deposition or dissolution of metals

A

kinetic polarization

30
Q

is the current per unit surface area of the electrode

A

current density

31
Q

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

A

kinetic polarization

32
Q

2 general types of electrogravimetric methods

A

potential of the working electrode
potentiostatic method

33
Q

maintains the working
electrode potential at a constant value
relative to a reference electrode

A

potentiostat

34
Q

The electrolysis current passes
between the working electrode and
a ____________. The ________ has no effect on the reaction at the working electrode

A

counter electrode

35
Q

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.

A

depolarizer

36
Q

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

A

coulomb

37
Q

the quantity of electrical charge required to convert a sample of an analyte quantitatively to a different oxidation state is measured

A

coulometric methods

38
Q

are usually rapid and do not require that the product of the electrochemical reaction be a weighable solid.

A

coulometric methods

39
Q

is the basis of the other electrical quantities, current, voltage, and power

A

electrical charge

40
Q

charge of electron or proton

A

1.6022x10^-19 C

41
Q

Two methods have been developed that are based on measuring the quantity of charge

A

controlled-potential (potentiostatic) coulometry
controlled-current coulometry

42
Q

often called coulometric titrimetry

A

controlled-current coulometry

43
Q

are similar to other titrimetric methods in that analyses are based on measuring the combining capacity of the analyte with a standard reagent

A

coulometric titrations

44
Q

is the change brought about by
1 mol of electrons

A

one equivalent of chemical change

45
Q

In ________, the potential of the working electrode is maintained at a constant level such that only the analyte is responsible for conducting charge across the electrode/solution interface.

A

controlled-potential coulometry

46
Q

is automated and equipped with a computer or an electronic current integrator that gives the charge in coulombs necessary to complete the reaction

A

potentiostat

47
Q

have been used to determine more than
55 elements in inorganic compounds and consists of an electrolysis cell, potentiostat, and a device for determining the charge consumed by the analyte

A

controlled-potential couloometric methods

48
Q

has been used in the nuclear energy field for the relatively interference-free determination of uranium and plutonium.

A

Controlled-potential coulometry

49
Q

re performed with a constant-current source, sometimes called a galvanostat, which senses decreases in current in a cell and responds by
increasing the potential applied to the cell until the current is restored to its original
level

A

coulometric titrations

50
Q

Constant-current generators are
sometimes called

A

galvanostats

51
Q

requires no preliminary calibration against chemical standards because the functional relationship between the quantity measured and the analyte concentration can be derived from theory and atomic mass data

A

electrogravimetry

52
Q

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

A

voltage

53
Q

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

A

mass transfer

54
Q

factors that influence polarization

A
  1. electrode size, shape, and composition
  2. composition of the electrolyte solution
  3. temperature and stirring rate
  4. current level
  5. physical state of the species participating in the cell
55
Q

TRUE or FALSE
The rate at which ions migrate to or away from an electrode surface generally increases as the electrode potential increases. This charge movement constitutes a current, which also increases with potential.

A

TRUE

56
Q

TRUE or FALSE
Migration causes anions to be attracted to the positive electrode and cations to the negative electrode

A

TRUE

57
Q

experimental varibales that influence the degree of concentration polarization are

A
  1. reactant concentration
  2. tota electrolyte concentration
  3. mechanical agitation
  4. electrode size
58
Q

is the electrode at which the analytical reaction
occurs.

A

working electrode

59
Q

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

A

potentiostatic method

60
Q

what cells use tall-form beakers are often
used, and solutions are usually mechanically stirred to minimize concentration polarization.
The anode is often rotated to act as a mechanical stirrer

A

electrolysis cells

61
Q

is particularly useful for removing easily reduced elements as a preliminary step in an analysis. For
example, copper, nickel, cobalt, silver, and cadmium are separated at this electrode from such ions as aluminum, titanium, the alkali metals, sulfates, and phosphates

A

mercury cathode

62
Q

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

keywords: tartrate ion to complex the tin (IV)

A

controlled potential electrolysis

63
Q

Faraday’s constant

A

96 485 C/mol e-

64
Q

applications of coulometric titrations

A

neutralization titration
precipitation and complex-formation reactions
redox titration

65
Q

neutralization titration is less susceptible to carbonate error, which is avoided through boiling the CP2 or by bubbling what insert gas

A

nitrogen

ANALYTICAL CHEMISTRY C3 (21 decks)

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