electroanalisis (elektrometri) potensiometri, amperometri and voltametri
TRANSCRIPT
![Page 1: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/1.jpg)
ELECTROANALISIS(Elektrometri)
Potensiometri, Amperometri and Voltametri
![Page 2: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/2.jpg)
Electroanalysis
• Mengukur berbagai parameter listrik (potensial, arus listrik, muatan listrik, konduktivitas) dalam kaitannya dengan parameter kimia (reaksi ataupun konsentrasi dari bahan kimia)
• Konduktimetri, Potensiometri (pH, ISE), Koulometri, Voltametri, Amperometri
![Page 3: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/3.jpg)
Potensiometri
Pengukuran potensial listrik dari suatu Sel Elektrokimia untuk mendapatkan informasi mengenai bahan kimia yang ada pada sel tsb (conc., aktivitas, muatan listrik)
Mengukur perbedaan potensial listrik antara 2 electroda:
Elektroda Pembanding (E constant)Elektroda Kerja/Indikator(sinyal analit)
![Page 4: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/4.jpg)
Elektroda Pembanding
Ag/AgCl:Ag(s) | AgCl (s) | Cl-(aq) || .....
- +
Ag/AgClSalt bridge
KCl
Pt
Fe2+, Fe3+
- +
Ag
Soln. aq. satdin KCl + AgCl
Pt
Fe2+, Fe3+AgCl + KCl
AgCl
Porous glass
AgCl(s) + e - <=> Ag(s) + Cl -
E0=0.222V
Fe3+ + e - <=> Fe2+
E0=0.771VE(KCl sat.)=0.197V
![Page 5: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/5.jpg)
Elektroda Pembanding
SCE:Pt(s) | Hg(l) | Hg2Cl2 (l) | KCl(aq., sat.) ||.....
Hg(l)
Soln. sat. in KCl
Pt
KCl
Hg, Hg2Cl2 et KCl
Porous glass
E0=0.268V
E(KCl sat.)=0.241VGlass wool
Hg2Cl2 + 2e - <=> 2Hg(l) + 2Cl -
![Page 6: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/6.jpg)
Elektroda Pembanding
• Reaksi/Potensial setengah selnya diketahui• Tidak bereaksi/dipengaruhi oleh analit yang diukur
– Reversible dan mengikuti persamaan Nernst– Potensial Konstan– Dapat kembali ke potensial awal– stabil
• Elektroda Calomel– Hg in contact with Hg(I) chloride (Hg/Hg2Cl2)– Ag/AgCl
![Page 7: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/7.jpg)
Electroda Kerja• Inert:
Pt, Au, Carbon. Tidak ikut bereaksi.
Contoh: SCE || Fe3+, Fe2+(aq) | Pt(s)
• Elektroda Logam yang mendeteksi ion logamnya sendiri (1st Electrode)(Hg, Cu, Zn, Cd, Ag)
Contoh: SCE || Ag+(aq) | Ag(s)
Ag+ + e- Ag(s) E0+= 0.799V
Hg2Cl2 + 2e 2Hg(l) + 2Cl- E-= 0.241V
E = 0.799 + 0.05916 log [Ag+] - 0.241 V
![Page 8: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/8.jpg)
Electroda Kerja
• Ecell=Eindicator-Ereference
• Metallic– 1st kind, 2nd kind, 3rd kind, redox
1st kind– respond directly to changing activity of electrode
ion– Direct equilibrium with solution
![Page 9: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/9.jpg)
2nd kind• Precipitate or stable complex of ion
– Ag for halides– Ag wire in AgCl saturated surface
• Complexes with organic ligands– EDTA
3rd kind– Electrode responds to different cation– Competition with ligand complex
![Page 10: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/10.jpg)
Metallic Redox Indictors
Inert metals – Pt, Au, Pd
• Electron source or sink• Redox of metal ion evaluated
– May not be reversible
![Page 11: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/11.jpg)
Membrane Indicator electrodes– Non-crystalline membranes:
• Glass - silicate glasses for H+, Na+• Liquid - liquid ion exchanger for Ca2+• Immobilized liquid - liquid/PVC matrix for Ca2+ and
NO3-– Crystalline membranes:
• Single crystal - LaF3 for FPolycrystalline• or mixed crystal - AgS for S2- and Ag+
Propertieso Low solubility - solids, semi-solids and polymerso Some electrical conductivity - often by dopingo Selectivity - part of membrane binds/reacts with analyte
![Page 12: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/12.jpg)
Glass Membrane Electrode
![Page 13: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/13.jpg)
Ion selective electrodes (ISEs)
A difference in the activity of an ion on either side of a selective membrane results in a thermodynamic
potensial difference being created across that membrane
C a 2 + C a 2 + 0 . 0 1 M C a 2 +
0 . 0 2 M C l -
0 . 1 M C a 2 +
0 . 2 M C l -
( 0 . 1 + ) M C a 2 + ( 0 . 1 - ) M C a 2 +
0 . 0 2 M C l - 0 . 2 M C l -
+
+
+
+
-
-
-
-
Calcium selective molecular recognition ligand
![Page 14: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/14.jpg)
ISEs
25C) (@
log0592.0
ln
ln
2
1
2
1
2
1
A
A
nA
A
nF
RTE
nFEA
ARTG
![Page 15: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/15.jpg)
Combination glass pH Electrode
Ag
Soln. aq. satdin KCl + AgCl
AgCl(s) + KCl(s)
AgCl porousglass
+ -
0.1M HCl inAgCl sat.
![Page 16: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/16.jpg)
Proper pH Calibration• E = constant – constant.0.0591 pH• Meter measures E vs pH – must calibrate both slope & intercept on
meter with buffers• Meter has two controls – calibrate & slope• 1st use pH 7.00 buffer to adjust calibrate knob• 2nd step is to use any other pH buffer• Adjust slope/temp control to correct pH value• This will pivot the calibration line around the isopotensial which is set to
7.00 in all meters
mV
pH 4 7
Calibrate knob raisesand lowers the linewithout changing slope
mV
pH 4 7
Slope/temp control pivots line around isopotensialwithout changing it
![Page 17: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/17.jpg)
Liquid Membrane Electrodes
![Page 18: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/18.jpg)
Solid State Membrane Electrodes
Ag wire
Filling solutionwith fixed[Cl-] andcation thatelectroderesponds to
Ag/AgCl
Solid state membrane(must be ionic conductor)
Solid State Membrane Chemistry
Membrane Ion Determined
LaF3 F-, La3+
AgCl Ag+, Cl-
AgBr Ag+, Br-
AgI Ag+, I-
Ag2S Ag+, S2-
Ag2S + CuS Cu2+
Ag2S + CdS Cd2+
Ag2S + PbS Pb2+
![Page 19: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/19.jpg)
Solid state electrodes
![Page 20: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/20.jpg)
VOLTAMETRI Pengukuran arus sebagai fungsi perubahan potensial
POLAROGRAFI:• Heyrovsky (1922): melakukan percobaan voltametri
yang pertama dengan elektroda merkuri tetes (DME)
Cu2+ + 2e → Cu(Hg)
![Page 21: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/21.jpg)
![Page 22: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/22.jpg)
Mengapa elektron berpindah
EF
Eredox E
F
Eredox
Reduction Oxidation
E E
![Page 23: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/23.jpg)
Steps in an electron transfer eventO must be successfully transported
from bulk solution (mass transport)O must adsorb transiently onto
electrode surface (non-faradaic)CT must occur between electrode and
O (faradaic)R must desorb from electrode surface
(non-faradaic)R must be transported away from
electrode surface back into bulk solution (mass transport)
![Page 24: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/24.jpg)
Mass Transport or Mass Transfer• Migration – movement of a muatan listrik listrik particle in a
potensial field• Diffusion – movement due to a concentration gradient. If
electrochemical reaction depletes (or produces) some species at the electrode surface, then a concentration gradient develops and the electroactive species will tend to diffuse from the bulk solution to the electrode (or from the electrode out into the bulk solution)
• Convection – mass transfer due to stirring. Achieved by some form of mechanical movement of the solution or the electrode i.e., stir solution, rotate or vibrate electrodeDifficult to get perfect reproducibility with stirring, better to move the electrodeConvection is considerably more efficient than diffusion or migration = higher arus listriks for a given concentration = greater analytical sensitivity
![Page 25: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/25.jpg)
Nernst-Planck Equation
xx
x
RT
F
x
xx CCDzCDJ iii
iiii
Diffusion Migration Convection
Ji(x) = flux of species i at distance x from electrode (mole/cm2 s)Di = diffusion coefficient (cm2/s)Ci(x)/x = concentration gradient at distance x from electrode(x)/x = potensial gradient at distance x from electrode(x) = velocity at which species i moves (cm/s)
![Page 26: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/26.jpg)
Diffusion
Solving Fick’s Laws for particular applications like electrochemistry involves establishing Initial Conditions and Boundary Conditions
Fick’s 1st Law
I = nFAJ
![Page 27: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/27.jpg)
Simplest ExperimentChronoamperometri
time
i
![Page 28: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/28.jpg)
Simulation
![Page 29: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/29.jpg)
Recall-Double layer
![Page 30: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/30.jpg)
Double-Layer charging
• Charging/discharging a capacitor upon application of a potensial step
RCtc e
R
EI /
Itotal = Ic + IF
![Page 31: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/31.jpg)
Working electrode choice
• Depends upon potensial window desired– Overpotensial– Stability of material– Conductivity– contamination
![Page 32: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/32.jpg)
The polarogrampoints a to b
I = E/Rpoints b to c
electron transfer to the electroactive species.
I(reduction) depends on the no. of molecules
reduced/s: this rises as a function of Epoints c to d
when E is sufficiently negative, every molecule that reaches the electrode
surface is reduced.
![Page 33: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/33.jpg)
Dropping Mercury Electrode
• Renewable surface• potensial window expanded for reduction
(high overpotensial for proton reduction at mercury)
![Page 34: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/34.jpg)
PolarographyA = 4(3mt/4d)2/3 = 0.85(mt)2/3
Mass flow rate of dropDensity of drop
We can substitute this into Cottrell Equation
i(t) = nFACD1/2/ 1/2t1/2
Giving the Ilkovich Equation:
id = 708nD1/2m2/3t1/6C
I has units of Amps when D is in cm2s-1,m is in g/s and t is in seconds. C is in mol/cm3
This expression gives the arus listrik at the end of the drop life. The average arus listrik is
obtained by integrating the arus listrik over this time period
iav = 607nD1/2m2/3t1/6C
We also replace D by 7/3D to account for the compression of the diffusion layer by the expanding drop
![Page 35: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/35.jpg)
Polarograms
E1/2 = E0 + RT/nF log (DR/Do)1/2 (reversible couple)
Usually D’s are similar so half wave potensial is similar to formal potensial. Also potensial is independent of concentration and can therefore be used as a diagnostic of identity of analytes.
![Page 36: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/36.jpg)
![Page 37: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/37.jpg)
![Page 38: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/38.jpg)
Other types of Polarography
• Examples refer to polarography but are applicable to other votammetric methods as well
• all attempt to improve signal to noise
• usually by removing capacitive arus listriks
![Page 39: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/39.jpg)
Normal Pulse Polarography
![Page 40: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/40.jpg)
NPP advantage
![Page 41: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/41.jpg)
Differential pulse voltametri
![Page 42: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/42.jpg)
DPP vs DCP
Ep ~ E1/2 (Ep= E1/2±DE/2)
1
-1
(
cnFAD1/2
mp tI
where DE=pulse amplitude
s = exp[(nF/RT)(DE/2)]
Resolution depends on DEW1/2 = 3.52RT/nF when DE0
Improved response because charging arus listrik is subtracted and adsorptive effects are discriminated against.l.o.d. 10-8M
![Page 43: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/43.jpg)
Resolution
![Page 44: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/44.jpg)
Stripping voltametri• Preconcentration technique.
1. Preconcentration or accumulation step. Here the analyte species is collected onto/into the working electrode
2. Measurement step : here a potensial waveform is applied to the electrode to remove (strip) the accumulated analyte.
![Page 45: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/45.jpg)
Deposition potensial
![Page 46: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/46.jpg)
ASV
![Page 47: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/47.jpg)
ASV or CSV
![Page 48: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/48.jpg)
![Page 49: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/49.jpg)
![Page 50: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/50.jpg)
Multi-Element
![Page 51: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/51.jpg)
Standard Addition
![Page 52: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/52.jpg)
Cyclic voltametri• Cyclic voltametri is carried out at a stationary
electrode. • This normally involves the use of an inert disc
electrode made from platinum, gold or glassy carbon. Nickel has also been used.
• The potensial is continuously changed as a linear function of time. The rate of change of potensial with time is referred to as the scan rate (v). Compared to a RDE the scan rates in cyclic voltametri are usually much higher, typically 50 mV s-1
![Page 53: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/53.jpg)
Cyclic voltametri• Cyclic voltametri, in which the direction of the potensial
is reversed at the end of the first scan. Thus, the waveform is usually of the form of an isosceles triangle.
• The advantage using a stationary electrode is that the product of the electron transfer reaction that occurred in the forward scan can be probed again in the reverse scan.
• CV is a powerful tool for the determination of formal redox potensials, detection of chemical reactions that precede or follow the electrochemical reaction and evaluation of electron transfer kinetics.
![Page 54: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/54.jpg)
Cyclic voltametri
![Page 55: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/55.jpg)
Cyclic voltametri
For a reversible process
Epc – Epa = 0.059V/n
![Page 56: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/56.jpg)
The Randles-Sevcik equation Reversible systems
![Page 57: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/57.jpg)
The Randles-Sevcik equation Reversible systems
214463.0 RTnFvDnFACip
• n = the number of electrons in the redox reaction• v = the scan rate in V s-1
• F = the Faraday’s constant 96,485 coulombs mole-1
• A = the electrode area cm2
• R = the gas constant 8.314 J mole-1 K-1
• T = the temperature K• D = the analyte diffusion coefficient cm2 s-1
ACDvnip212123510687.2
![Page 58: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/58.jpg)
The Randles-Sevcik equation Reversible systems
As expected a plot of peak height vs the square root of the scan rate produces a linear plot, in which the diffusion coefficient can be obtained from the slope of the plot.
![Page 59: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/59.jpg)
Cyclic voltametri
![Page 60: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/60.jpg)
Cyclic voltametri
![Page 61: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/61.jpg)
Cyclic voltametri
![Page 62: ELECTROANALISIS (Elektrometri) Potensiometri, Amperometri and Voltametri](https://reader038.vdocuments.site/reader038/viewer/2022102403/56649c6e5503460f9491fb9c/html5/thumbnails/62.jpg)
Cyclic voltametri – Stationary Electrode
• Peak positions are related to formal potensial of redox process
• E0 = (Epa + Epc ) /2
• Separation of peaks for a reversible couple is 0.059/n volts
• A one electron fast electron transfer reaction thus gives 59mV separation
• Peak potensials are then independent of scan rate
• Half-peak potensial Ep/2 = E1/2 0.028/n
• Sign is + for a reduction