CHEM 2010 E3 (fJB)
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75 Terms
What is reduction potential?
The voltage produce by or required to add electrons to an atom or ion
What is oxidation potential?
The voltage produced or required to remove electrons from an atom or ion.
What is standard reduction potential?
The reduction potential compared to SHE and when analyses are at 25°C and 1 M or 1 barr.
What type of cell is spontaneous?
Galvanic
What kind of cell is NOT spontaneous?
Electrolytic
Express coulombs in units of amps and seconds.
A*s
What constant is equal to one mole?
Faraday’s constant
The reaction rate is proportional to what measurement?
Current
Work done is proportional to what?
Potential
An ion selective electrode requires that you create what in order to give useful information?
A calibration plot
What kind of measurements/experiments are done with ion selective electrodes?
Potentiometric
What does the reference electrode do?
Maintain potential to measure standard reduction potential
Can reference electrodes be double junctioned?
Yes
What does an indicator electrode do?
Responds to analyte concentration as indicated by potential difference from reference electrode.
Why does junction potential occur?
Potential difference between contact of 2 different electrolyte solutions
How many kinds of indicator electrodes were covered?
3
How do the 3 indicator electrodes work?
Metal, non-selective
Responds to changes in ion concentration by formation of a complex.
Responds to changes in ion concentration other than in the electrode.
How do ISEs work?
They respond preferentially to one species in solution, but not(e) interferences
What do ISEs determine?
Activities, not concentrations.
How is potential difference measured in ISE?
Across the membrane
What other electrodes are ISEs?
Polymer membrane electrodes, solid state electrodes, glass membrane electrodes
Is a calibration curve necessary for ISE, and if so, what does it determine?
Yes. It determines concentration.
What are the 3 kinds of indicator electrodes mentioned?
Metal, non-selective
Ag/AgCl as a Cl- sensor
ISEs
What are the membranes in polymer membrane electrodes?
Ion exchange materials in inert complexes.
Polymer membrane electrodes potential info
Potential developed at electrode surface and related to concentration of analyte
Glass membrane electrodes info
Formed by doping SiO2 glass matrix with various species, includes H+ and Na+
Solid state electrode info
Insoluble inorganic salts in the membrane, and potential is developed at membrane surface due to ion exchange process
Which side of the liquid junction potential 0.1 M AgCl | 0.1 M AgNO3 will be positive?
The left
The presence of a high concentration of what ion in solution interferes with the accurate measurement of pH?
Na+
An ion selective electrode has selectivity coefficients kNa+,K=2.1E-7 , kNa+,Rb+=1.7E-5 , and kNa+,Cs+=0.33. Which species interferes the most with the analysis of the concentration of Na+?
Cs+ because it has the highest selectivity coefficient.
What kind of electrode was the pH electrode used in lab?
Combination
How does electrogravimetric analysis work?
Analyte is plated onto the electrode and then weighed.
What is coulometric analysis?
How much current occurs (total number of electrons transferred) to determine analyte presence
What does coulometric analysis measure in units?
Current * time
What kind of electrochemical operation happens?
Electrolysis
Amperometry measures what, and what is it proportional to?
Current. The amount of analyte present.
What is held constant in amperometry?
Potential
What’s the purpose of a reference electrode?
It provides a reference the measure current across working and auxiliary electrodes.
What is controlled in reference electrodes?
Potential
What’s the purpose of a working electrode?
Its surface is the site for redox of species
Is potential controlled in working electrodes?
Yes
What’s the purpose of an auxiliary electrode?
It’s an inert electrode used to carry current in redox reactions
Where to redox reactions occur in 3-electrode systems?
On the working and auxiliary electrodes.
Why is a 3-electrode system better than a 2-electrode system?
You’ll get more stable/predictable potential values.
In a glucose meter, how many cells are there, and how many electrodes do they have individually?
2 and 2
What electrodes are in a glucose meter?
1 reference and 2 indicator electrodes
What kind of biosensor do glucose monitors have?
Amperometric
What interferes with glucose measurement by glucose meters?
Acetaminophen, uric acid, and citric acid
What does the top indicator in a glucose monitor measure?
Glucose signal and interferrents
What does the bottom indicator electrode in a glucose monitor measure?
Signal of interferrents
Why were the values recorded in the glucose lab so bad?
No salt with pure glucose solution to conduct electricity
How do glucose meters work?
Glucose oxidase oxidizes glucose, takes electrons to ferrocene cation, and reduces it to ferrocene, then electron transferred to indicator electrode
How many electrodes are used in amperometric detection with chromatography?
3
What is held constant in amperometric detection?
Potential
Where is current measured in an amperometric electrode?
Working electrode
What is current proportional to in an amperometric electrode system?
Analyte concentration
How many electrodes are in a voltammetry cell?
3
Is potential held constant in voltammetry?
No. It’s varied with time
What is controlled in voltammetry?
Diffusion (no stirring)
What is plotted in voltammetry?
Current vs potential
Is a calibration plot required for voltammetry?
Yes
What is proportional to the amount of analyte in voltammetry?
Peak current
What is polarography?
Voltammetry with mercury dropping working electrode
What is polarography useful for and why?
Reductions be a use H+ doesn’t reduce as well at Hg site
What isn’t polarography useful for and why?
Oxidation because Hg is oxidized easily at low potentials
What is a polarogram?
Voltammogram in polarography
What is the point of interest in polarography?
Half wave potential (E sub 1/2), which is redox potential
What is half-wave potential?
The midpoint of the slope
What can affect/change a polarogram?
Faradaic and charging currents
What is square wave voltammetry?
Uses waveform and staircase to calculate current between two points of potential
What is stripping analysis?
Using mercury drop electrode, analyte from dilute solution goes into drop of mercury by electroreduction. The potential increases to positive until analyte is stripped from electrode by oxidation.
What is measured in stripping analysis?
Current
What is current proportional to in stripping analysis?
Analyte concentration
What is stripping analysis good for?
Metal ions
What is good about stripping analysis?
It’s highly sensitive