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Topic: Electrodes for electrolysis  (Read 24879 times)

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Offline Scratch-

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Electrodes for electrolysis
« on: April 04, 2004, 10:48:27 AM »
I have tried using graphite electrodes in electrolysis but they erode like every other metal does, even though I read in the posts of another website that they dont erode. I am wondering if gold electrodes will not erode, I have some gold but it is gold dust so I would need to melt it to make electrodes and I dont want to do all that unless I know that gold doesnt erode.

Thanks


Edit: edited title for better indexing. Mitch
« Last Edit: April 24, 2004, 07:17:36 PM by Mitch »
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Offline Donaldson Tan

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Re:Electrodes
« Reply #1 on: April 04, 2004, 11:08:39 AM »
Does the products of your electrolysis include oxygen? btw gold is among the most inert metal
« Last Edit: April 04, 2004, 11:09:57 AM by geodome »
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Re:Electrodes
« Reply #2 on: April 04, 2004, 11:12:12 AM »
Yes, I am using water as a medium to break down salts, the problem with most electrodes is that they erode away and form metal hydroxides in the solution. Graphite doesnt form a hydroxide becouse its a nonmetal but it erodes anywase, limiting the amount of time before I have to replace an electrode.
« Last Edit: April 04, 2004, 11:13:46 AM by Scratch- »
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Offline Donaldson Tan

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Re:Electrodes
« Reply #3 on: April 04, 2004, 11:18:47 AM »
Do u know that electrolysis of water occurs when u attempt to use water as medium? Anions in higher concentration are discharged preferentially.

In a dilute solution, OH- will be discharged to produce oxygen, unless u use a concentrated salt solution such as brine. The reaction is as follows:
4OH-(aq) => O2(g) + 2H2O(l) + 4e

Erosion of graphite electrodes follows this reaction:
C(s) + O2(g) => CO2(g)

 ;)
« Last Edit: April 04, 2004, 11:20:10 AM by geodome »
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Re:Electrodes
« Reply #4 on: April 04, 2004, 11:31:53 AM »
Yes, that is why, for example, my electrolysis of NaCl produces sodium hydroxide and chlorine instead of sodium and chlorine. I don’t have the equipment to melt the salts and do electrolysis directly. I understand that the hydrogen and oxygen released into the solution play a part in eroding the electrodes. But I am just an amateur chemist awaiting my first year of high school chemistry (taken at a college, duel enrollment Wohoo  ;D), still I follow most of your equation there. So gold wolnt erode like graphite will, how will using a more concentrated solution prohibit the production of OH-?
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Offline Donaldson Tan

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Re:Electrodes
« Reply #5 on: April 04, 2004, 11:40:17 AM »
The more concentrated anion will discharge preferentially. That's all. The solution becomes increasingly alkali because of residual hydroxide ion formed from discharging the hydrogen cations. Perhaps adding aq zinc(II) chloride to the mixture. Any excess hydroxide will be precipitated as Zinc(II) Hydroxide during the electrolysis process. (just a suggestion)
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Re:Electrodes
« Reply #6 on: April 04, 2004, 11:46:31 AM »
 :o, Uhhh.... En Ingles, por favor? lol  :P
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Re:Electrodes
« Reply #7 on: April 04, 2004, 11:49:54 AM »
I dont understand the non-english u had posted..

Zinc(II) cation won't be discharged preferentially, at the same, it reacts with hydroxide ion to produce the insoluble zinc(II) hydroxide - a white precipitate.

The chloride anion will contribute to the chloride concentration.
« Last Edit: April 04, 2004, 12:11:44 PM by geodome »
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Re:Electrodes
« Reply #8 on: April 04, 2004, 11:59:33 AM »
What I said was "In English, please", I haven’t heard some of the words you just said. I read in a book once that a normal language and the technical language are very different, almost like another language... Anyway, so adding zinc chloride will break down, the zinc will react with the ion and precipitate out because its insoluble and the chlorine will bubble off, is that what you meant?
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Re:Electrodes
« Reply #9 on: April 04, 2004, 12:06:35 PM »
Aq Zinc(II) Chloride will remove the residual hydroxide, thus help prevent the discharge of hydroxide ions.

Zinc(II) cation won't be discharged as it's more stable than the hydrogen cation (with reference to their standard electrode potential).

Chlorine will bubble off as usual.
« Last Edit: April 04, 2004, 12:09:10 PM by geodome »
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

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Re:Electrodes
« Reply #10 on: April 04, 2004, 12:25:50 PM »
Thanks
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Offline Mitch

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Re:Electrodes
« Reply #11 on: April 04, 2004, 05:23:22 PM »
I use graphite electrodes and they work like a champ for me. Are you just trying to use any old graphite? The graphite used has to be specific for electrodes.
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Re:Electrodes
« Reply #12 on: April 04, 2004, 07:01:50 PM »
Any old graphite, I dont have easy access to a chemical store so I have to improvise. I am wondering if I can use gold electrodes that I can get from melting the gold dust I panned in Alaska.
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Offline Mitch

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Re:Electrodes
« Reply #13 on: April 04, 2004, 07:25:52 PM »
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3807007991&category=12578

Gold dust is the hard way to do it, I think you can get any hardware store to special order it for you.
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Re:Electrodes
« Reply #14 on: April 04, 2004, 07:32:41 PM »
I couldnt melt a small amount of gold into one piece and pound it into a foil?
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