Consult with your laboratory instructor about the content and format of your report for this experiment. The following are suggestions and considerations regarding the content.
Note: With computerized potentiostats you may be able to use Math function to determine Ep and Ip values. Similarly, the Ip values can often be corrected for the background charging current.
- Write a short summary of what you did in this experiment, noting any deviations or substitutions in the procedure. Show example cyclic voltammograms.
- Plot Ip vs. concentration of ferricyanide. It should be linear (background corrected?). Determine the concentration of the unknown sample of ferricyanide from this calibration plot.
- Determine the Eo’ value from the voltammograms. If the values vary with the scan rate, plot them versus the scan rate and extrapolate to obtain the Eo’ at zero scan rate. Compare this value with the tabulated formal potential of ferri/ferrocyanide in 0.1 M HCl.
- Tabulate the difference between Epc and Epa values – are they close to the theoretical value for a reversible electrode reaction? If not, can you account for the deviation?
- Plot Ipa and Ipc vs. ν1/2, and from the slope, determine the value of the diffusion coefficient (must measure the electrode area). How does your value compare to the literature one of 0.62 x 10-5 cm2/s? Should there be a difference in the diffusion coefficient between ferricyanide and ferrocyanide? If so, why?
- The Ipc/Ipa = 1 for a diffusion controlled reversible electrode reaction. [Note: the baseline needs to be extrapolated by drawing the best straight line so that the Ipc and Ipa can be corrected for the background solution] Do you get unity for this ratio from your CV experiments?
- There is a current decrease at ~ 100 mV past Ipc or Ipa due to the concentration of the species being electrolyzed going to zero at the electrode surface. This condition is similar to that found in chronoamperometry where the rate is diffusion controlled. Under such a condition, the current decreases as a function of 1/[t]1/2. Do a plot of I vs. t1/2, starting at ~ 60 mV past Ep and see if you get a linear plot. Does the same condition apply also to the anodic wave?
- Calculate δ at Ip of a CV at a scan rate of 100 mV/s, assuming t = 0 occurs at the start of the rising portion of the CV wave. This value of δ is only a rough approximation but will give you a "feel" for dimensions of the diffusion layer thickness.