Calculate Diffusion Coefficient K4Fe(CN)6 Cyclic Voltammetry

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In summary, the conversation involves calculating the diffusion coefficient of ferricyanide using cyclic voltammograms. The peak currents at different scan rates were given, and the slope of the line was found to be 76.747. However, after isolating for D, the calculated value was significantly different from the theoretical value. The mistake was suspected to be in the concentration units used, but it was clarified that it would not affect the slope calculation. Further discussion revealed that there may be other factors affecting the accuracy of the calculated value.
  • #1
zeromaxxx
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Homework Statement



Calculate the diffusion coefficient (cm2/s) of ferricyanide if cyclic voltammograms conducted on a solution of 1 mM KClO4 + 5 mM K4Fe(CN)6 at scan rates of 1, 2, 5, 10, 20, and 50 mV/s, resulted in peak currents of 76, 100, 175, 243, 348 and 552 mA. The electrode used for the experiment had been modified with a polymeric coating an effective area of 0.56 cm2.

Homework Equations



ipc=(269000)n3/2AD1/2C v1/2

A=0.56 cm2
n=1
C= 0.000005 mol/cm3

The Attempt at a Solution



I ploted the ipc vs. v1/2 and found the slope of the line which was approx. 76.747

ipc/v1/2 = 76.747

Isolating for D =[76.747/((269000)n3/2AC)]2

=[76.747/((269000)13/20.56x0.000005)]2

= 10 382.51

which is clearly wrong since the theoretical value of D is 7.6 x 10-6

Can anyone point out my mistake? I have a feeling it's with the concentration though I'm not quite sure...
 
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  • #2
What units ipc should be in? mA or A?
 
  • #3
Borek said:
What units ipc should be in? mA or A?

it should be A but does that make a difference when the slope is calculated? since v1/2 is in mV/s and the slope would pretty much amount to the same value of 76.747?
 
  • #4
zeromaxxx said:
it should be A but does that make a difference when the slope is calculated? since v1/2 is in mV/s and the slope would pretty much amount to the same value of 76.747?

That's not how it works.
 
  • #5
zeromaxxx said:
it should be A but does that make a difference when the slope is calculated? since v1/2 is in mV/s and the slope would pretty much amount to the same value of 76.747?

That's not how it works.
 

1. What is diffusion coefficient in the context of cyclic voltammetry?

The diffusion coefficient in cyclic voltammetry refers to the rate at which a species diffuses through a solution under an applied electrical potential. It is a measure of how quickly the species moves through the solution and is influenced by factors such as temperature, viscosity, and concentration.

2. Why is it important to calculate the diffusion coefficient in cyclic voltammetry?

The diffusion coefficient is an important parameter in cyclic voltammetry as it affects the shape and magnitude of the voltammogram, which is used to analyze the electrochemical behavior of a species. It also provides information about the kinetics and thermodynamics of the redox reaction being studied.

3. How is the diffusion coefficient calculated in cyclic voltammetry?

The diffusion coefficient in cyclic voltammetry is typically calculated using the Randles-Sevcik equation, which relates the current, applied potential, and scan rate to the diffusion coefficient and other parameters such as the electrode area and concentration of the species in solution.

4. What is the significance of the K4Fe(CN)6 complex in calculating diffusion coefficient?

The K4Fe(CN)6 complex is commonly used as a standard in cyclic voltammetry experiments to calculate the diffusion coefficient. Its well-known electrochemical behavior and known diffusion coefficient make it a reliable reference for comparison with other species being studied.

5. How does temperature affect the diffusion coefficient in cyclic voltammetry?

The diffusion coefficient is directly proportional to temperature, meaning that as temperature increases, the diffusion coefficient also increases. This is because higher temperatures increase the kinetic energy of the species, allowing them to diffuse more quickly through the solution.

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