This document describes an experiment using cyclic voltammetry to determine the concentration of iron in an unknown sample solution. Five standard solutions with known iron concentrations were used to generate a calibration curve by plotting peak current versus concentration. Cyclic voltammograms were recorded for each standard solution and the unknown. The peak currents from the unknown were used to determine its concentration from the calibration curves, calculating it to be 5.37 mM from the anodic curve and 4.48 mM from the cathodic curve. The experiment aimed to quantify the analyte and determine reaction reversibility but had some limitations around minimizing liquid junction potentials and ensuring an inert atmosphere.

1. Voltammetric Determination of Iron
NAME: S. M. ABU
NAYEEM
ID: 1702021
Chem-352
Experiment No: 03
Instrumental Methods of Analysis

2. Introduction
 Voltammetry: Measure current at a different applied potential.
 Different types of voltammetry:
Linear Scan Voltammetry Cyclic Voltammetry Square Wave Voltammetry
Applied
Voltage, V
Time
Applied
Voltage, V
Time
Applied
Voltage, V
This type of voltammetric method
is used in the experiment
Time
Slope = scan rate

3. Introduction
 Voltammogram: A diagram represents the variation of current with the applied
cyclic voltage.
 Electrochemical cell: Potential or energy generator which induces electron to
flow.
Source of energy : Chemical reaction.

4. Theoretical Background
Three types of current
1. Capacitive current/ Non- Faradic/ Double layer current
2. Faradic current
3. Diffusion current
Three modes of mass transport of the analyte
1. Convection ( due to action of mechanical forces)
2. Migration ( due to applied electric field)
3. Diffusion (due to concentration gradient)

5. Theoretical Background
Chemical reaction occurs
(Faradic current)
No chemical reaction
(Non Faradic current)
Source of current : Movement of ions.
Source of current: Diffusion+

6. Experimental Procedure
 Five 100 mL solution including four known concentration
and an unknown concentration were prepared.
 Each of the solutions were put into the cell and voltage were
applied with 100 mV/s scan rate.
 The cyclic voltammogram for all the solutions were
recorded.
 The calibration graph was drawn showing the measures Ipc
as a function of the concentration of the solutions based on
the calibration series.
 Using the calibration curve, the concentration of the
unknown sample solution was determined.

7. Data Processing
Observed
voltammogram
Sample
Concentr
ation
Ipa (mA) Epa (V) Ipc (mA) Epc (V)
1 0.78 5.90 0.23 -3.70 0.15
2 2.34 12.30 0.24 -10.30 0.17
3 3.90 21.20 0.25 -22.60 0.165
4 7.80 33.50 0.24 -35.80 0.16
5 Unknown 24.80 0.25 -21.70 0.16
Table 1: Data obtained from cyclic voltammetry
curves for different concentration samples.

8. Data Processing
Sample
Concentra
tion
Ipa (mA) Epa (V) Ipc (mA) Epc (V)
1 0.78 5.90 0.23 -3.70 0.15
2 2.34 12.30 0.24 -10.30 0.17
3 3.90 21.20 0.25 -22.60 0.165
4 7.80 33.50 0.24 -35.80 0.16
5 Unknown 24.80 0.25 -21.70 0.16
5.37
4.48
y = 3.94x + 3.6274
y = -4.6326x - 0.9363
-50
-40
-30
-20
-10
0
10
20
30
40
0 2 4 6 8 10
Peak-current Concentration(mM)
Peak-current vs concentarion
Unknown Sample
Unknown Sample
Linear (Calibartion curve for
anodic peak current, Ipa)
Linear (Calibartion curve for
cathodic peak current Ipc)
From anodic pic current calibration curve concentration, x = 5.37 mM
From cathodic pic current calibration curve concentration, x = 4.48 mM

9. Results
Observation
Anode Section
Cathode
Section
Concentration
(mM)
Concentration
(mM)
Unknown
Solution
5.37 4.48
Amount of Iron
(mole)
5.37×10-4 4.48×10-4
Calculation:
• From anodic pic current:
Concentration, S = 5.37 mM ; Volume, V = 100 mL
⸫Moles of Iron, n = S (in mole)×V(in L)
=(5.37×10-3×100×10-3) mole
= 5.37×10-4 mole
• From cathodic pic current:
Concentration = 4.48 mM ; Volume = 100 mL
⸫Moles of Iron = (4.48×10-3×100×10-3) mole
= 4.48×10-4 mole
Table 2: Concentration of unknown sample

10. Discussion
Major limitations that caused errors
1. Liquid junction potential was not minimized properly. (Reason: Different ionic mobilities of
ions)
2. Theoretical treatment excludes migration and convection of the analyte and this are not
minimized properly.
3. Anodic pic current and cathodic pic current was measured manually.
4. Inert atmosphere was not ensured properly done. ( N2 is inert but O2 undergoes reversible
reaction)

11. Conclusion
 Quantitative analysis of analyte.
 Reversibility of a redox reaction. [ If ∆Epeak=59mV (for n=1 and 25℃) or Ipc/Ipa=1 and if
Ipc/Ipa<1 but a return pic is present this reaction is pseudo reversible ]
 Formal potential ( E0 = (Epa+Epc)/2 ) determination.
 Catalyst performance analysis.
 Diffusivity or diffusion coefficient measurement. ( ip=k*(𝐷 ∗ 𝑣)1/2
, where k is constant
for a certain system)

12. References
I would like to thank the authors of the articles
“A Practical Beginner’s Guide to Cyclic Voltammetry” by Noemie Elgrishi , Kelley J. Rountree, Brian D. McCarthy,
Eric S. Rountree, Thomas T. Eisenhart, and Jillian L. Dempsey (DOI:10.1021/acs.jchemed.7b00361)
“Cyclic voltammetry experiment,” by James J. Van Benschoten, Jane Y. Lewis (DOI:10.1021/ed060p772)
“Cyclic Voltammetry,” by Marken F., Neudeck A., Bond A.M. (2005). In: Scholz F. (eds) Electroanalytical Methods.
Springer, Berlin, Heidelberg. (DOI:10.1007/978-3-662-04757-6_4)