Bulk Electrolysis: Electrogravimetry and Coulometry

Question 1

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.

Answer 1

electrogravimetry and coulometry

Question 2

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

Answer 2

electrogravimetry

Question 3

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

Answer 3

coulometry

Question 4

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

Answer 4

IR drop and polarization

Question 5

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

Answer 5

Ohmic potential

Question 6

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

Answer 6

ohmic potential or IR drop

Question 7

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

Answer 7

direct current

Question 8

is the rate of charge flow in a circuit or solution

Answer 8

current

Question 9

direction always reverses unidirectionally, ac

Answer 9

alternating current

Question 10

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

Answer 10

three-electrode cell

Question 11

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

Answer 12

overvoltage

Question 13

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

Answer 13

overvoltage or overpotential

Question 14

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

Answer 14

polarization

Question 15

polarization phenomena can be divided into two categories

Answer 15

concentration polarization and kinetic polarization

Question 16

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

Answer 16

concentration polarization

Question 17

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.

Answer 17

concentration polarization

Question 18

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

Answer 18

diffusion
migration
convection

Question 19

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.

Answer 19

diffusion

Question 20

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

Answer 20

TRUE

Question 21

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 21

diffusion

Question 22

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.

Answer 22

migration

Question 23

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

Answer 23

supporting electrolyte

Question 24

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.

Answer 24

convection

Question 25

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 25

forced convection

Question 26

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

Answer 26

natural convection

Question 27

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

Answer 27

convection

Question 28

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

Answer 28

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

Question 29

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

Answer 29

kinetic polarization

Question 30

is the current per unit surface area of the electrode

Answer 30

current density

Question 31

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

Answer 31

kinetic polarization

Question 32

2 general types of electrogravimetric methods

Answer 32

potential of the working electrode potentiostatic method

Question 33

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

Answer 33

potentiostat

Question 34

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

Answer 34

counter electrode

Question 35

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 35

depolarizer

Question 36

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

Answer 36

coulomb

Question 37

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

Answer 37

coulometric methods

Question 38

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

Answer 38

coulometric methods

Question 39

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

Answer 39

electrical charge

Question 40

charge of electron or proton

Answer 40

1.6022x10^-19 C

Question 41

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

Answer 41

controlled-potential (potentiostatic) coulometry controlled-current coulometry

Question 42

often called coulometric titrimetry

Answer 42

controlled-current coulometry

Question 43

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

Answer 43

coulometric titrations

Question 44

is the change brought about by 1 mol of electrons

Answer 44

one equivalent of chemical change

Question 45

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.

Answer 45

controlled-potential coulometry

Question 46

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

Answer 46

potentiostat

Question 47

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

Answer 47

controlled-potential couloometric methods

Question 48

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

Answer 48

Controlled-potential coulometry

Question 49

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

Answer 49

coulometric titrations

Question 50

Constant-current generators are sometimes called

Answer 50

galvanostats

Question 51

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

Answer 51

electrogravimetry

Question 52

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

Answer 52

voltage

Question 53

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

Answer 53

mass transfer

Question 54

factors that influence polarization

Answer 54

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

Question 55

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.

Answer 55

TRUE

Question 56

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

Answer 56

TRUE

Question 57

experimental varibales that influence the degree of concentration polarization are

Answer 57

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

Question 58

is the electrode at which the analytical reaction occurs.

Answer 58

working electrode

Question 59

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

Answer 59

potentiostatic method

Question 60

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

Answer 60

electrolysis cells

Question 61

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

Answer 61

mercury cathode

Question 62

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)

Answer 62

controlled potential electrolysis

Question 63

Faraday's constant

Answer 63

96 485 C/mol e-

Question 64

applications of coulometric titrations

Answer 64

neutralization titration precipitation and complex-formation reactions redox titration

Question 65

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

Answer 65

nitrogen