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Homework Help: Cyclic Voltammetry

  1. Nov 9, 2011 #1
    1. The problem statement, all variables and given/known data

    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.

    2. Relevant equations

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

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

    3. 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...
     
  2. jcsd
  3. Nov 9, 2011 #2

    Borek

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    Staff: Mentor

    What units ipc should be in? mA or A?
     
  4. Nov 9, 2011 #3
    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?
     
  5. Nov 10, 2011 #4

    Borek

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    Staff: Mentor

    That's not how it works.
     
  6. Nov 10, 2011 #5

    Borek

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    Staff: Mentor

    That's not how it works.
     
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