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Indicator Electrodes, Potentiometry, Electrochemistry, Electrode Kinetics, Electrogravimetry, Polarography, Square Wave Voltammetry, Wavelength Selection, Types of Spectroscopy, Detectors, Theory of Molecular Absorption, Absorption by Organic Molecules, Applying UV-vis Spectroscopy are major topics of this course. Main points from these slides are: Membrane Electrodes, Liquid Junction, Solid State, Permeable, Glass Ph Electrode, Ph Calibration, Combination Ph Electrode, Liquid Membrane Electrode
Typology: Slides
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with AgClcoatedAg wire Filling solution0.1 M HCl seal connectionElectrical
Thin glass membrane
electrode- Permeable membraneelectrode- Solid State membrane- Liquid membrane electrode- Glass membrane electrode
Ag/AgClresponds toelectrodecation that[Cl-] andwith fixedsolutionFilling Solid state membrane
(must be ionic conductor)
Pb 2+
Ag
(^2) S + PbS
Cd 2+
Ag (^2) S + CdS
Cu 2+
Ag (^2) S + CuS
Ag (^) , S+
2-
Ag (^2) S
Ag (^) , I+
AgI
Ag (^) , Br+
AgBr
Ag (^) , Cl+
AgCl
F , La-
3+
LaF
3
Ion Determined
MembraneSolid State Membrane Chemistry
(^3) ) is the key component of electrode
(^4) + ] which
responds to changes in [NH
(^3) ] passing
membrane according to
NH
3
(^2) O
NH
(^4) +
(blue)membraneGlass electrode^ pH
(yellow)permeablegasmembrane -Hydrophobic
(gray)solutionFilling
(^3) diffuses through membrane
(^3) in test solution equilibrates
with NH
(^3) in filling solution
NH (^3)
NH (^4) +
[NH
(^4) + ][OH
]-
K b = ----------------------
[NH
(^3) ]
K b
[OH
] = --------- [NH-
(^3) ]
[NH
(^4) + ]
pH = 14 – pOH = pNH
3
Diagram of CO
2
Reference electrodeshowing internalgas sensing probe is hydrophobicbecause membranein the filling solutionbehind membranemust be locatedReference electrode
(blue)membraneGlass electrode^ pH
(yellow)permeablegasmembrane -Hydrophobic
(gray)solutionFilling
on the surface of the NHa thin layer of the enzyme ureasecan be prepared by immobilizingAn electrode sensitive to urea
3 electrode
O
H (^2) N-C-NH
(^2)
2 NH
(^3)
2
3
& CO
2 in this enzyme layer
-NH
(^3) diffuses through
membrane to give response
Enzyme layer
In all electrochemical methods, the rate of which depend on:at electrode surface (electrode kinetics),2) kinetics of the electron transfer processreach electrode surface (mass transport)1) rate & means by which soluble speciesoxidation & reduction depend on:
c) temperatureb) nature of electrode surfacea) nature of the reaction
(we don’t have much control over #2)
Migration – movement of a charged
In most cases migration is undesirable and(important for conductance & electrophoresis)particle in a potential field – generally bad
migrating, not the analytereduced) Inert electrolyte does theelectrochemically inert – not oxidized orexcess of an inert electrolyte (i.e.,can be eliminated by adding a 100 fold
In all electrochemical methods, the rate of which depend on:at electrode surface (electrode kinetics),2) kinetics of the electron transfer processreach electrode surface (mass transport)1) rate & means by which soluble speciesoxidation & reduction depend on:
c) temperatureb) nature of electrode surfacea) nature of the reaction
(we don’t have much control over #2)
st Law^
cm= flux of material i.e., moles passing a 1
(^2) plane at point x & time t (mol/cm
/sec)^2
(^) = diffusion coefficient (cm
/sec)^2
(^) = concentration
= time (sec) from when power is turned on
(^) = distance from electrode surface (cm)
