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30 Cards in this Set

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What is concentration polarization?
A condition in which the current in an electrochemical cell is limited by the rate at Which reactants are brought to or removed from the surface of one or both electrodes.
What is Kinetic Polarization?
A condition in which current in an electrochemical cell is limited by the rate at Which electrons are transferred between the Electrode surfaces and reactants in solution. For either type of polarization, the current is no longer proportional to the cell potential.
What is a amperostat?
An instrument that provides a constant current.
What is a potentiostat?
An instrument that provides an electrical output having a constant potential.
What is a coulomb?
A quantity of charge transported by one ampere of current in one second.
What is a Faraday?
One Faraday is equal to 96,495 coulombs or one mole of electrons.
What is a working electrode?
The electrode at which the desired electrochemical reaction is carried out.
What is a counter electrode?
A electrode that is used with working electrodes to complete the electrical circuit in a cell. It is connected to the Working electrode by an external metallic conductor.
What is a electrolysis circuit?
Consists of a working electrode and a counter electrode.
What is a control circuit?
Regulates the applied potential such that the potential between the working electrode and a reference electrode in the control circuit is constant and at a desired level.
What is current density?
The current at an electrode divided by the surface area of that electrode. Ordinarily it has units of amperes per square centimeter.
What is ohmic potential or
IR drop?
the product of the current in amperes and the electrical resistance in ohms.
What is a coulometric titration?
An electroanalytical method in which a constant current of known magnitude generates a reagent that reacts with the analyte. The time required to generate enough reagent to complete the reaction is measured.
What is a controlled-potential the potential applied to a cell is continuously electrolysis?
Adjusted to maintain a constant potential between the working electrode and a reference electrode.
What is current efficiency?
A measure of agreement between the number of faradays of current and the number of moles or reactant oxidized or reduced at a working electrode.
What is overvoltage?
The increased potential required to offset the decrease in current brought about by polarization.
What are the three methods
responsible for the mass transport of dissolved species to and from a electrode surface?
diffusion, migration, and convection.
What is diffusion?
Arises from concentration differences between the electrode surface and bulk of the solution.
What is migration?
Results from electrostatic attraction or repulsion between the species and an electrode.
What is convection?
Results from stirring, vibration, and temperature differences.
How does the existence of a current affect the potential of an electrochemical cell?
current in an electrochemical cell always causes the cell potential to become less positive or more negative.
How do concentration polarization And kinetic polarization resemble One another and differ from one Another?
Both kinetic and concentration polarization cause the potential of a cell to be more negative than the thermodynamic potential. Concentration polarization arises from the Slow rate at which reactants or products are transported to or away from the electrode surfaces. Kinetic polarization arises from the slow rate of the electrochemical reactions at the electrode surfaces.
What experimental variables affect Concentration polarization in a electrochemical cell?
Variables that decrease concentration polarization include elevated temperatures,vigorous stirring, high reactant Concentrations, absence of other electrolytes and a large electrode surface areas.
How do electrogravimetric and Coulometric methods differ from potentriametric methods?
Potentiometric measurements are made under conditions of zero (or almost zero)current; electrogravimetric and coulometric methods depend upon the presence of a current.
What is the purpose of depolarizer?
It is a substance that is reduced more readily than a potentially interfering species. The codeposition of hydrogen, for example, is prevented through the introduction of nitrate ion as a depolarizer.
What is a potentiostat?
The applied potential to maintain constant potential between the working electrode and a reference electrode.
What is the difference between
voltammetry and polarography?
Voltammetry is a analytical technique that is based upon measuring the current that Develops in a microelectrode as the applied
Potential is varied. Polarography is a particular type of voltammetry in which the microelectrode is a dropping mercury electrode.
What is the difference between limiting current and residual current?
A residual current in polarography is a nonfaradaic charging current that arises from the flow of electrons required to charge individual drops of mercury as they form and fall. A limiting current is a constant faradiac current that is limited in magnitude by the rate at which a reactant is brought to the surface of a microelectrode.
Why is a high supporting electrolyte concentration used in most electro analytical procedures?
the supporting electrolyte removes the concentration of migration to the diffusion current thereby maintaining the proportionality of Id and concentration.
Why is a solution of Cu(NH3)
blue?
a solution of Cu(NH3) is blue because this ion absorbs yellow radiation and transmits blue radiation unchanged.