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MEDL-210 MB > Module 9: Electrochemistry > Flashcards

Module 9: Electrochemistry Flashcards

1
Q

Cation

A

pos charged ion

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2
Q

Anion

A

neg charged ion

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3
Q

Basic 4 parts of electrochemical cells

A

electrolyte solution
2 electrodes
meter or power supply

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4
Q

LEO says GER

A

Lose of e- = oxidation at ANODE (metal ions enter solution, leaving electrons on the electrode)
Electrons travel through external connection to cathode (passing a meter)
Gain of e- = Reduction at CATHODE (metal ions come out of solution to be deposited on the electrode as solid metal)

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5
Q

how to rebalance a solution after redox reaction

A

anions must travel through salt bridge (porous plug) that connects the two solutions

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6
Q

If the salt bridge becomes clogged,

A

anions could not move through to balance the charge differences
Flow of electrons between 2 electrodes would stop

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7
Q

Nernst Equation

A

calculates potential voltage when 2 half-cells are joined
Potential is directly proportional to log of ionic activity in the solution

“0.0591/n” in equation is the SLOPE FACTOR and can be used as an indicator of the sensitivity of the electrode

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8
Q

2 different potential generating principles

A 
Metallic (electrode generated potential; reference electrodes)
Membrane potential (indicator electrode)
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9
Q

Metallic (electrode generated potential)

A

Reference electrodes are this type
When a metal is placed into solution of its own ions, a potential is produced that is related to the concentration of ions in solution

Low concentration = metal ions pass into solution, leaving neg charge on metal electrode
High concentration = fewer metal ions pass into solution; neg charge on metal electrode will be smaller (very little dissociation occurs therefore good as reference electrode)

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10
Q

Membrane Potential

A

2 solutions of different ionic activity (concentration) are separated by thin membrane
Oppositely charged ions will be attracted across the membrane
Potential is generated by the difference in charges in each solution

++++++++
xxxxxxxxx membrane
- - - - - - -

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11
Q

Which principles are employed in indicator electrodes

A

BOTH metallic and membrane potential

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12
Q

Potentiometric measurement systems consists of (4)

A

reference electrode
indicator electrode
meter
standards (buffers) used for calibration

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13
Q

Reference electrode

A

Provides constant and stable potential to compare the varying potential of indicator electrode to
HIGH concentration of electrolyte solution

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14
Q

Common reference electrodes

A

**Saturated calomel electrode: mercury covered in a thin coating of calomel immersed in solution of KCl

Silver/Silver chloride electrode: silver covered in a thin coating of silver chloride immersed in solution of KCl

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15
Q

Indicator electrode

A

responds to activity of ions in an unknown sample
LOW concentration of electrolyte solution (allows detectable change in potential)
Membrane electrode
Commonly designed to measure H+ in a solution

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16
Q

Operation of pH indicator electrode

A

Dip membrane into sample
H+ from sample collects on outside of membrane
Attracts negative ions to inside of membrane
Developed membrane potential
No negative ions in solution; salt moves into solution to balance charge
Metal ions left over

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17
Q

Meter

A

voltmeter
measure difference between reference and indicator electrode
displays as ionic concentration
3 parts: Amplifier, operating adjustments, display

18
Q

Standards (buffers) for calibration

A

solution of known concentration

used to make cal curve

19
Q

As temp increases, dissociation

A

increases

20
Q

Ion selective electrodes (ISE)

A

membrane electrode capable of responding with great sensitivity to one kind of ion while having lower sensitivity to others
sensitivity is determined by type of membrane used
Glass membrane
Solid-state membrane
Liquid ion exchange membrane
Immobilized Enzyme
Gas-sensing
Disposable ISE (vitros potentiometric slides)

21
Q

Glass membrane ISE

A

sensitivity depends on the formation of glass

Used for: H+, Na+, Li+, NH4+

22
Q

Solid-state membrane ISE

A

no internal electrolyte solution

Used for : sweat chloride

23
Q

Liquid Ion Exchange Membrane ISE

A

porous disc
consists of an inert solvent in which an ion selective carrier is embedded
One side of disc = internal reference solution with known concentration of ion
Other side of disc = unknown test solution
Used for : K+

24
Q

Liquid ion exchange membrane ISE: membrane selective for K+

A

are made by dissolving the antibiotic valinomycin in a solvent

25
Q

Immobilized Enzyme Electrodes

A

Combines specific enzyme bound to some form of inert support with an indicator system that responds to a by-product of the enzyme substrate reaction
Used for: urea, glucose, creat, ethanol, lactate

26
Q

Gas-sensing electrodes

A

addition of gar-permeable membrane
Specificity is derived from the selective permeability of the membrane
Analyte gas passes through membrane into internal solution when it is sensed by indicator electrode

27
Q

Common gas sensing electrode

A

CO2 electrode

Selectivity is provided by a gas permeable silicone rubber membrane

28
Q

Disposable ISEs

A

AKA Vitros Potentiometric Slides
Used mainly in “dry chemistry”
Use 2 indicator electrodes (concentration cells)
One receives reference solution and other receives unknown
The difference is measured

29
Q

Voltammetry (polarography)

A

refers to methods that measure current through a cell where voltage is controlled
Current produced is related to the concentration of the reactive ions to be measured

30
Q

Amperometry

A

Measurement of the current flowing that is produced by a redox reaction

31
Q

Common Amperometry cell

A

O2 electrode with platinum wire immersed in a buffer
Buffer is separated from sample by gas permeable membrane (often polypropylene)
Electrons consumed during reaction are drawn from cathode which causes more current flow to cathode to replace
Increased flow is proportional to the O2 in the sample

Can also be used to measure glucose (enzyme added as reagent)
O2 electrode can detect the consumption of O2

32
Q

Conductivity

A

the greater the # of ions present in a solution, the better the ability to conduct current

33
Q

Conductimetry

A

measurement of current flow between 2 electrodes immersed in a solution
Used in hematology cell counters
Dilution of whole blood drawn through aperture
1 electrode on either side of the aperture
Current flow between electrodes drops when cell passes through (based on size of cell)

34
Q

Coulometry

A

Electrochemical titration
end point is detected by a change in current
Ex: titration of chloride using chloridometer; platinum electrode and silver electrode use to make up the generator electrodes
Applied voltage oxidized Ag electrode and Ag+ is titrated into the solution
Ag reacts with Cl- to form insoluble precipitate of AgCl
When all the Cl- from sample is consumer, the Ag+ appears in excess causing an increase in current (detected by a paid of indicator electrodes)

35
Q

Direct ISE

A

undiluted sample

36
Q

Indirect ISE

A

measure a diluted sample

Aliquot of sample is taken and diluted with reference solution, then mixture is measured by the system

37
Q

Interference with Lipemia and high protein sample

A

Indirect only

Small diluted aliquot taken for measurement may have fat glob in it, making results falsely low

38
Q

Interference from similar ions

A

membranes are selective not specific
may display some level of interference by other ions of similar structure
Ex. Cl- electrodes can display interference from high levels of bromine

39
Q

Protein buildup

A

ISE may become coated with protein buildup from running large numbers of samples

40
Q

Electrode fatigue

A

electrode may become fatigued with extended use or large numbers of tests in a row
Can be reconditioned by allowing it to sit in a reference solution

MEDL-210 MB (13 decks)

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