Ferricyanide: A Cyclic Voltammetry Analysis

Ferricyanide; A Cyclic Voltammetry analysis

Analytical Lab 1: 2410 L

Name: Austin Stevens

Lab Partners:

3:05-5:55 Group 2

Date: 10/12/15

Introduction: This Experiment was done to determine the concentration of an unknown, the half-wave potential, and to the determine the calibration curve of the reduction of ferricyanide to ferrocyanide through the use of cyclic voltammetry1: Fe(CN)63- + e- ↔ Fe(CN)64- Cyclic voltammetry uses the knowledge of voltammetry; which is the measure of a typical current response caused by an electrical current which is captured on an electrode and then measured, to determine potentials2. Cyclic voltammetry is one major proponent of voltammetry. Cyclic voltammetry

To measure this three electrodes are used, a glassy carbon working electrode, an Ag/AgCl reference electrode, and an auxiliary electrode which is made of platinum (Pt wire)2. An electrical current is passed from the working to the auxiliary electrode, then as noted above, the current is switched. This creates four distinct parameters; an anodic peak current (ipa), cathodic peak current (ipc), anodic peak potential (Epa), and the cathodic peak potential (Epc)1. These values can be used to determine the half-cell potential, an unknown concentration and

For figure 4a that relationship is not linear, R2 = 0.64 and 0.39 respectively. Although if 10 mM is removed from the equation, R2 values of 0.997 and 0.997 can be found. This helps prove that there is a relationship between the concentration and current.

Table 2b. Data for determining the concentration of the unknown ferricyanide solution Peak Current (A) Calibration Line

Cathodic 3.00E-5 y = 6.00E-6x 1.00E-6

Anodic 2.15E-5 y = 5.00E-6x  1.00E-6

Calculation 3: Cathodic scan of unknown concentration

X=(3.00E^(-5)+1.00E^(-5))/(4.00E^(-6) )= 10mM

For Table 2a, the value for the cathode unknown is 10 mM while the anode is 1.53 mM. There is an 85% difference between the two which is most likely to be caused by the 10mM outlier. Now if the 10 mM data values are removed the results are 5.2 mM for the cathode and 4.5 mM for the anode. This is a 15% difference between the two calculated unknowns. Although the percent difference is not idea, it is considerably better than the values show in Table 2a.

Figure 5. Unknown solution cyclic voltammogram; 20 mV/s scan rate.

Scan Rate: Figure 6. Scan rates of 10, 50, 75, 100, 150, and 200 mV/s for 4 mM