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Reduce diffusion effects in electrolysis

  1. Sep 18, 2010 #1
    How could i reduce the effect of diffusion of ions in an electrolysis cell. e.g AgNO3 Ag+

    Stirring constanly would help? but thats not easily kept fair or constant. Could i replace this idea with rotating electrodes?

    Many Thanks, Adam
     
  2. jcsd
  3. Sep 19, 2010 #2
    Could someone also explain diffusion in more detail. i think ive grasped it biology wise, e.g in the body.
     
  4. Sep 19, 2010 #3

    Borek

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    What are you trying to do?

    It is hard to "explain diffusion", not knowing what you are looking for. Diffusion is a transport process based on random motion of molecules, described by Fick's laws.

    --
    methods
     
  5. Sep 19, 2010 #4
    Im evaluating my experiment. One of the ways i could improve it would to get rid f the effect of diffusion. When i electrolysed my 3 solutions, high concentration of ion areas ( generally in the solution) diffused into low concentratio areas ( around the cathode ), this would be different, random, and make the test unfair.

    How could i reduce the randowm effect of diffusion. One way would to stir the solution constantly, this would be difficult, so could i use rotating electrodes, to create a vortex is it? and make this fairer.

    Are there any other ways?

    Thanks
     
  6. Sep 19, 2010 #5

    Borek

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    While diffusion is an effect of random motions, it is not random on the normal experimental scale, quite the opposite. If you take a static (not stirred) solution, and you keep everything identical between the experiments, results are highly repeatable. That's base of all chronovoltamperometric methods. If the experiment is too long (that is, electrolysis step takes more than just a few seconds) you will face problems, but not because of the diffusion. Diffusion is predictable, convection is not, and it will be convection that will make your results off.

    What are you using electrolysis for?
     
  7. Sep 19, 2010 #6
    just chemistry coursework. we electrolysed for 2 mins. part of the problem is nothing was kept constant, diffusion wasnt constant because the three 'constants' we had, wernt kept consant. I=nAve , we changed 'e'; charge of electron.

    Theres more about my experiment here : https://www.physicsforums.com/showthread.php?t=419345&page=3

    So could i get rid of the effect of diffusion by using rotating electrodes?

    Thanks again
     
  8. Sep 20, 2010 #7

    chemisttree

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    Probably not completely. If rotation were fast enough to create a vortex, you would have a depletion zone more pronounced at the bottom of the electrode than at the top, assuming the vortex conveyed material from the top downward. If no vortex were formed, you would have a depletion or enrichment zone that extended radially from or to the electrodes. I believe in commercial plating operations, air is bubbled from the bottom of the cell for stirring.

    Also, if you overvoltage the electrodes, you can produce gases. These gas bubbles form on the electrode and have the effect of reducing the electrode surface area until they detach. So bubbles that form and are more persistent (large bubbles) have a larger effect than bubbles that detach when tiny. Surfactants might encourage one over the other. I would use nonionics to minimize any charge-charge effects.
     
  9. Sep 20, 2010 #8

    Borek

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    Simple magnetic stirrer should do. If it gives repeatable results when doing trace analysis of metals on mercury electrodes, it will be good enough for your experiment.
     
  10. Sep 20, 2010 #9
    Thankyu, yes that seems fine for the job :)
     
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