Mitchell
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Copper Cathode Electrolysis
To start out this isn't another chlorate post. As I realize how much it is frowned upon among the sciencemadness community. I not trying ruin
someones day by posting about chlorate cells. My objective here is to figure out why my copper cathode keeps dissolving. In my electrolosys
expariment. Here's a run down of my set up. I have a about two table spoons of salt dissolved in distilled water.I am running nine volts by one amp
via a wall transformer.My anode is platinum and my cathode is copper and here lies the problem. when turning on the cell the vicinity of the copper
electrode instantly becomes green. probably copper chloride. But, I don't want to know what the product is I want to know the reaction. From my
understanding, the anode does the dissolving. while sodium hydroxide and hydrogen gas is evolved from the cathode. neither of those products react
with copper.So why is the copper corroding. I am also aware that hypochlrorite is produced. I can see how that could oxidize in which the NaOH could
react. To see if this was the case I threw a clean copper scrap in the previously mentioned solution. guess what ......nothing. So I am fairly sure
that its not the bleach thats makeing the copper ions go into solution.
I have been thinking for the past few days why this is happening. If I understand why maybe I can apply this concept to future projects. BTW my aim is
not to create a chlorate cell I have titanium electrodes for that.
thank you for any helpful responses
Mitchell
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bfesser
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Thread Moved
31-7-2013 at 20:20 |
Artemus Gordon
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AFAIK, it's impossible for Cu to form negative ions, so it seems to me that your Cu electrode is behaving as an anode, not a cathode. What happens
when you reverse the polarity? What if you replace the NaCl with NaOH or Na2SO4 or HCl or H2SO4? What if you replace the Pt electrode with another Cu,
or Zn or Mg?
When something doesn't work the way you expect it to, that's when the fun science begins!
"The secret is to bang the rocks together, guys."
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Artemus Gordon
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One more thing. If you reverse polarity and you cell behaves the same, your wall transformer may be giving you AC rather than DC.
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ElectroWin
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you must rectify the current. the cell wants DC, not AC.
connect your cathode to the [ - ] terminal, anode to the [ + ] terminal.
http://www.rapidonline.com/catalogueimages/module/M067301P01...
[Edited on 2013-8-01 by ElectroWin]
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Pulverulescent
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To "read up on electro-chemistry" is the best advice I can offer the OP . . .
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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papaya
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Little off-topic, but I see in chlorate related topics that the most common 'resistant' material for cathode mentioned is SS. Lead can be even better
I think, if you don't have a lead sheet you can take a copper sheet and with the help of soldering iron spread a thin layer of solder(containing lead)
on surface of it. Once I made such a cathode that showed no signs of corrosion in 24 hours, I don't think that this will affect yield of chlorate in
any way.
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Mitchell
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So based on the first point.I have tried using MgSO4 as an electrolyte and using the same electrodes the solution around the copper cathode still
turned blue. I also tried reversing the polarity and it behaved as I expected. After about an hour the platinum cathode was covered with spongy copper
and the solution was really blue which I assume is copper sulfate. I am working on converting a power supply unit into a regular power supply. This
way I can have pure DC power. Any way during the normal running of the cell( negative-copper... Positive-platinum) none of the spongy copper is plated
on to the platinum which leads me to believe that there is no ac current. In the mean time I I'll try using a regular 9v battery and see if it
produces any copper ions thank you for your responses
Mitchell
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Mitchell
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Oh I almost forgot, when I reversed the polarity of the salt cell the copper was anode and platinum was cathode.I observed that the copper anode
stayed very shiny for a very long time. It also took about 5 min for the solution to turn blue green. (using the same 9v transformer power
supply)platinum cathode had no reaction.
When I run the cell normaly(copper cathode-platinum anode) the copper cathode turns black instantly. The solution near the cathode turns green
after about 30 seconds. Not the 5 min it takes for the solution to turn blue green when I reverse the polarity. Thats why I think there is some weird
reaction going on that has nothing to do with the power supply. Yet I have not totally ruled that out. During all of these expariments I was using the
9v power transformer. I am still working on trying to convert my PC power supply.
Mitchell
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12AX7
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Good bet you've confused the anode and cathode. And your electrolyte is probably all kinds of nasty (copper contamination, and other things maybe?).
Tim
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Pulverulescent
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And are you using a wall-wart . . . ?
A wall-wart powering a Pt anode would seem comically incongruous! 
Get yourself a 'proper' PSU . . .
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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Artemus Gordon
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"That's why I think there is some weird reaction going on that has nothing to do with the power supply. "
One thing to try is to set up your cell and let it sit with no power. Another would be to use 2 Cu electrodes. If they both change color, that would
indicate you had electrons moving both ways.
Since you have a 9 volt supply, and redox reactions usually take only 1-2v, you are nearly shorting your supply. This might possibly cause high
amounts of AC ripple. You might try a 5-20 ohm resistor in series with your cell to drop the excess 7 volts. This might slow down the reaction, but it
also might make your power source a lot cleaner. Make sure the resistor can handle the wattage; one way to do it would be to solder 10 or so 100 ohm
1/4w resistors in parallel.
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Artemus Gordon
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Sheesh, I don't know why this didn't occur to me sooner: whenever you make an electrochemical cell with dissimilar electrodes, you have made a
battery. (I know I am not being precise in my terminology - deal with it.) Since Cu is more reactive than Pt, the Cu will naturally tend to act like
the anode. One might think that the power supply would overcome the battery's natural dynamics, but as I've said previously, your supply may be a far
cry from pure DC. Also, maybe the Cu atoms on the surface are being influenced more by the presence of the ionized electrolyte than they are by the
electrons coming from the power supply.
I think you should make both electrodes the same. Either 2 Cu or 2 Pt, but not one of each.
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Mitchell
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Thank you everyone for your responses.
I think I have solved the problem. So after finally getting an old power supply unit working. I tried the first expariment that I started with and,
You guessed it... (or not) the copper cathode did not dissolve whatsoever. So the problem was as many of you described... the damn wall wart. At least
I learned something. I always thought when the wall wart said 9v 1 amp DC! (was tempted to put like 30 exclamation points but I got to keep it civil
yo) that It meant it. let that be a lesson to the beginers dont use wall warts. Get a proper power supply. Another thing I learned is the word
incongruous thank you pulverulescent. I will also investigate AC ripple. Thanks again.
Regards. Mitchell
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Pulverulescent
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You're welcome.
I drove my first chlorate cell (many orbits ago) from a car battery charger trans., with a sec. rewound (fiddly as fuck!) to give ~4 V @ ~40 A!
The cost of Pt (with its only moderate conductivity) being inhibitive for such current-density, graphite gouging rods were used!
The rectifier hada 65 A rating and the ammeter went to 50 . . .
IMS, the cell held 3 L and ran @ >100°C!
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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