Lec 6 - Electrochemistry Flashcards
A term used when chemical energy is converted to electrical current in a galvanic cell or electrolytic cell.
Electrochemistry
The measurement of electrical signals associated with chemical systems that are incorporated in an electrochemical cell
Electrochemistry (2)
An electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell.
Galvanic cell
Loss of electrons
Oxidation
Gain of electrons
Reduction
Site of reduction
Cathode
Site of oxidation
Anode
An electrochemical cell where electric current causes the transfer of electrons in a redox reaction.
Electrolytic cell
___ cell uses the transfer of electrons in redox reactions to supply an electrical circuit.
Whereas, ___ cell requires current to cause the transfer of electrons in a redox reaction.
GALVANIC cell ___ the transfer of electrons in redox reactions to supply an electrical circuit.
Whereas, ELECTROLYTIC cell requires current to ___ the transfer of electrons in a redox reaction.
A process wherein electricity is used to make a chemical change.
Electrolysis
A basic category of Electrochemical Technique:
• measures voltage as volts
• measurement of a cell potential under equilibrium conditions.
• uses galvanic cell principle
Potentiometry
A basic category of Electrochemical Technique:
• measures current
• comprises the combination of voltage with amperometry.
Voltammetry
Voltammetry:
Voltage is ___?
Applied to the electrolytic cell consisting of 2 or 3 electrodes dipped into the solution.
Voltammetry:
Amperometry is ___?
The measurement of electric current flowing through the cell
Potentiometry (principle)
Measurement of electrical potential between 2 electrodes in a solution, and comparing those 2 to each other.
Potentiometric methods are best suited for measurement of ions such as __, __, and __.
Sodium, potassium and chloride
Types of potentiometric electrodes
Redox electrodes,
Ion-selective electrodes,
pCO2 electrodes
It measures the current in an electrochemical cell as a function of the applied potential.
Voltammetry
Types of voltammetry
Polarography,
Amperometry,
Stripping voltammetry,
Hydrodynamic voltammetry
Amperometry (Principle)
Measurement of current through an electrochemical cell when a potential is applied to the electrodes at a single applied potential.
Coulometry (principle)
Measurement of the quantity of electricity which is directly proportional to the chemical reaction at the electrode.
The measurement of the quantity of electricity at a fixed potential between 2 electrodes in an electrochemical cell.
Coulometry
Coulometry formula
Q = I x T
A current flow of 1 ampere per second
Coulomb
• 96,500 coulombs
Faraday
A coulometric titrator
Chloridometer
Chloridometer is used for measuring chloride ion concentration in biological fluids such as ___.
Urine,
Sweat,
CSF
An electric conductor that is in contact with an ionic conductor.
Electrode
An electrode wherein it acts as electron donor or electrical acceptor.
Passive (Inert) Electrode
An electrode wherein it acts as ion donor or electron acceptor.
Active (Participating) Electrode
Electron reaction
An electrochemical process in which charge transfer takes place at the interface between the electrode & electrolyte.
2 electrodes used in electrochemistry:
Indicator electrode, reference electrode
An electrode that:
• is sensitive and responds to changes in temperature.
• interacts with the analyte of interest.
• shows the activity of an ion in a solution
Indicator electrode
• most common indicator electrode
• measures a potential across a membrane specific for a certain analyte.
Ion-selective electrode
An electrode that:
• is used as a fix reference for the direct measurement of the potential between the electrode and solution.
• has a constant potential and voltage source
Reference electrode
3 reference electrodes
Standard Hydrogen electrode,
Saturated calomel electrode,
Silver / Silver chloride
____ electrode allows potentiometric measurement of a single type of ion without interference of other ions.
Ion-selective electrode
The ions that can be measured by Ion-selective electrode:
Sodium,
Potassium
Calcium,
Lithium,
Magnesium,
Chloride
Galvanic cell formula
Ecell = EISE – Eref
3 major types of ISE
- Inert metal electrode / Ion selective glass
✓ SHE - Metal / Solid state electrode
✓ Ag–AgCl - Membrane electrode / Liquid Ion exchange membrane
✓ Ca2+ selective electrode
• An electrode used as a sensor for hydrogen or sodium in biological solutions.
• has 3 dimensional matrix of varying oxides of elements
Glass Membrane
• A thin glass membrane
• has 3 layers that separate 2 solutions of different hydrogen ion activity
Hydrogen electrode
A glass electrode selectively permeable only to Na (sodium)
Sodium glass electrode
Basic types of MEMBRANES used in ISE
- Solid ion exchange
✓ glass membrane
✓ solid state crystal membrane - Liquid ion exchange
- Neutral carrier membrane
A solid ion exchange membrane that is:
• mechanically strong in thin sections
• chemically inert
• non-porous
• highly insoluble
Solid state crystal membrane
A membrane that consists of water-immiscible solvents which contain ionizable species preferentially soluble in the solvent phase.
Liquid ion exchange
ISE assay of Sodium (Na+)
Sample: _____
Anticoagulant: _____
Hemolysis effect: _____
Sample:
• serum, plasma, urine (24 hr), whole blood, sweat
Anticoagulant:
• Ammonium heparin, Lithium heparin, Lithium oxalate
Hemolysis effect:
• no significant change
— due to decreased levels of intracellular sodium
ISE assay of Potassium (K+)
Sample: _____
Anticoagulant: _____
Hemolysis effect: _____
Sample:
• serum, plasma, urine
Anticoagulant:
• N/A
Hemolysis effect:
• must be avoided
This results in release of K+ from the rupture of cell counts, causing spurious hyperkalemia
significantly elevated platelet counts results in release of K+ from the rupture of these cell counts, causing ____.
Describes the electromotive force generated by H+ at the glass tip
Nernst Equation
