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Saerynide
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The electrodes dont corrode too much if the cells are separated by a salt bridge, but then voltage drops by so much  I still need to get myself a multimeter to measure the voltage and current in my
cell.
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darkflame89
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Organikum, what do you mean by "not too happy with the H2SO4 part"? Aluminium sulphate hydrolyses all right right, the trouble is keeping
the result away from each other, that is prevent the aluminium hydroxide from reacting with H2SO4 again.
I tried the electrolysis of my produced CuSO4 again with pencil electrodes sharpened on both ends. The electrodes corroded away preetty fast. Carbon
powder was all over the solution in the end. And, at first the cathode side bubbled away with what i think is H2 gas. Cu(OH)2 also collected around
the electrodes. I think the CuSO4 concentration is too low. When i added more CuSO4 powders, the bubbling at the cathode side was reduced, and copper
started to form. The anode side corroded the fastest. The electricity stopped in 2 hours as the sharpened end of the pencil had disappeared into the
solution. Also, i will be away on a camp for the next 3 days, therefore i had to stop this experiment.
The pH however at this point of time is 4.
Ignis ubique latet, naturam amplectitur omnem.
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Organikum
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In my part of the world neither aluminium sulfate nor aluminium chloride nor ferric chloride hydrolyses easily to form the correspondending acids. In
the best scenario with heaps of water there will be some equilibrium building up, but by no way a complete decomposition of the sulfate/chloride will
take place. (not speaking of decomposition of the chlorides by heating - is understood).
Making aluminium sulfate is useless - there is no sense in this. Btw. why doesnt MgSO4 hydrolyse if Al-sulfate does?
Sorry to take your idea down. Making iron or copper sulfate and using this might be a good idea, but just changing the electrolyte when it gets basic
as I told before is a better idea.
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axehandle
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Electrode material.
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The process is taking too long to produce a small quantity of acid. The carbon electrodes, which are correded at high voltages must be replaced, but
with what?! If the carbon rods could be replaced by some other inert material (which is not gold and neither platinum ) the process could be scaled up
by increasing the voltage right? Does anyone have any suggestions.
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Why? Why not use gold or platinum? A flattened thin wire won't cost as much as you might imagine, and it will conduct far better than graphite.
I'd go with Pt as it's higher on the "inertness scale" than Au, but it's also twice as expensive.
Example: Take a 0.5mm thick Pt wire, 100mm long (to make 2 electrodes).
The volume of the metal is pi*(0.25*0.25)*100 cubic mm. This equals about 0.01963 cubic centimeters. The density of Pt is about 21, so the wire will
weigh about 0.41g. Such a wire would cost about 230SEK, equaling about 20 Euro. Not so horrible, no?
Have anyone BTW thought about using Ag? Would it be inert?
[Edited on 2004-4-11 by axehandle]
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Esplosivo
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Thanks axehandle. I've just checked and the minimun I can buy of Pt wire of a thickness of 0.46mm is 15 cms. I'll try to buy the wire soon,
though exams are getting near. This time will help me increase my budget  thanks
for the help
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axehandle
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a little warning
No worry, just make sure you don't accidentally use AC during the electrolysis if there is hydrocloric acid present in the fluid -- the Pt will
dissolve, forming hexacloroplatinic acid, which would be a very expensive way to ruin your day..... 
Edit: Also, if you get jewelry grade Pt, it's normally alloyed with 5 to 10 % Pd to make the Pt harder. That shouldn't matter though.
[Edited on 2004-4-12 by axehandle]
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Organikum
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Another example:
(from Ullmanns)
Zinc electrolysis:
- Cathode: Al
- Anode: Pb/Ag (plain lead will work)
I suggest the use of an lead anode in the MgSO4 electrolysis as the anodic part will be similar to the zinc-sulfate process. As long the concentration
of the MgSO4 doesnt drop to low a decomposition of the lead electrode will be no problem.
What I see being a problem here in the described experiments is that you all run your cells much too long without refilling electrolyte - this makes
your electrodes decompose. Use bigger cells or refill! Change the electrolyte in the cathode chamber and refill MgSO4 in the anode chamber from time
to time.
You really dont need Pt electrodes here.
[Edited on 12-4-2004 by Organikum]
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Saerynide
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But if you change the electrolytes, wont you be having salt in the acid? Can that be crystalized out by fractional crystalization? And, how do you
know when to change the solutions?
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Organikum
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When the ph in the cathode chamber gets low you might change the electrolyte in there and - refill MgSO4 in the anode chamber. I dont think you can
"overfill" the electrolyte in the anode chamber, so just fill in MgSO4 until it doesnt dissolve anymore. A graphite alectrode can be used as
anode - keeping temperatures below 50°C or less will help to protect it from decomposition. I dont know about the solubility of MgSO4 in concentrated
H2SO4 but I GUESS it will precipitate upon concentrating the sulfuric acid by boiling away the water.
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Saerynide
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The pH in the *cathode* gets *low*?? Doesnt the pH at the cathode get high
and becomes more basic?
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Organikum
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Yes ph gets high - more basic - my bad sorry.
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Saerynide
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Lol no prob. You had me scratching my head there for a while 
If I understand correctly what you're saying, I should do this:
Change the catholyte where the Mg(OH)2 is.
Add more MgSO4 to the anolyte where the H2SO4 is.
Is that right?
Man, I better buy some huge jars to store the spent catholyte so I can recycle whatever I can crystalize out
Edit: typos
[Edited on 12-4-2004 by Saerynide]
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axehandle
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mea culpa
Well, *hhrrrrm* *blushing*, yes, Pb is slightly less expensive than Pt..... although Pt has many other.... interesting.... applications.
KClO4, HNO3, H2SO4......
Edit: Btw, if I'm lucky I will have 4.5g of Pt tomorrow! Oh, yesssss, precioussssss........
[Edited on 2004-4-12 by axehandle]
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Saerynide
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Doesnt Pb turn to lead sulfate like in lead acid batteries?
Edit: Nice new title btw If I get this working, do I get a special title?
*sniff* 
[Edited on 12-4-2004 by Saerynide]
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axehandle
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| Quote: |
Doesnt Pb turn to lead sulfate like in lead acid batteries?
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Not according to Organikum, and he always knows what he's talking about. See a few posts above. Besides, if it did, it could probably be filtered
out easily --- and lead is cheap. I'd still go for Pt though.... or iridium...
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Edit: Nice new title btw If I get this working, do I get a special title? *sniff*
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I'd suggest brown-nosing a moderator. That's what I did.
[Edited on 2004-4-12 by axehandle]
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Organikum
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As seen I dont always know what I talk about - ph low and high, auwei.....
But as I took the Pb anode plain from the Ullmanns it should be right to the point. 
Maybe it is worth a try just to refill MgSO4 in both chambers - anode and cathode - the Mg(OH)2 should precipitate for being not soluble in water if
"Kings Chemical Survival Guide" is right. (I will look it up in the Merck later).
Anyways - replentishing the electrolyte is a logical MUST - it wont last forever. The possible concentration of H2SO4 should be quite high - 30%+
perhaps even 50% or more. At least this are the concentrations electrolytic zinc is made with - 30% starting and not higher as 50% if I remember
right. Lead anodes are used so this will be no problem.
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Esplosivo
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Organikum, lead reacts with sulphuric acid forming lead (II) sulpahte right? This lead (II) sulphate is insoluble (especially in the sulphuric acid
because of the common ion effect) and will therefore form a coating on the lead electrode. Now, ionic salts do conduct electricity, but in solution or
in the molten state, NOT in the solid state. How will the lead electrodes conduct electricity with a surface coating of lead (II) sulphate?!
Theory guides, experiment decides.
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axehandle
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I have a wild speculation: I suspect that the lead sulfate won't adhere to the lead anode, but sink to the bottom of the vessel due to the huge
density of lead. This is just an uneducated guess.
I'd still go with iridium-clad platinum.....
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Esplosivo
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I doubt that lead (II) sulphate would fall of the electrode. When reacting Pb with sulphuric acid a 'protective' coating of PbSO4 forms,
after which no more reaction occurs since the inner Pb is not in contact with H2SO4. But it might be different in the case of electrolysis, I
don't know.
[Edited on 12-4-2004 by Esplosivo]
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Organikum
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Lead is quite resistant to H2SO4 - thats why it was widely used in the production of the acid - look for "lead-chamber" or ask axehandle.
On the second side there is the prsence of the MgSO4 protecting the lead electrode - this will predominantly get decomposed - as told as long the
temperature is not to high and the concentration of the MgSO4 not too low the lead wont get attacked. (better: it will get attacked only a little bit
)
Ok, ok:
The Merck says lead reacts with HOT CONCENTRATED nitric, sulfuric and hydrochloric acid.
So it wont react with sulfuric acid if it is not to hot and too concentrated - as told 50°C and 50% will cause no problems - higher temps/conc.
probably will.
Formed lead-sulfate will dissolve in diluted H2SO4 but will precipitate upon concentrating the acid. It wont hurt anyways - I suppose nobody is going
to drink the selfmade H2SO4?
So we have two reactions to consider:
- the usual H2SO4 + Pb = lead-sulfate:
This takes not place at the named temperatures and concentrations
- the electrolytic decomposition of lead to form lead-sulfate like it car batteries:
This takes not place as long enough MgSO4 is present, as the electric energy is used up in the decomposition of the MgSO4. Only if your MgSO4
concentration would get to low you would start to decompose your electrode.
[Edited on 13-4-2004 by Organikum]
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Esplosivo
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Thanks a lot for the explanation Organikum. I guess I will try the electrolysis using lead plates obtained from car battries then.
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Saerynide
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Hm... now where to get lead :S
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Organikum
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ALL CAPS
CARBON CARBON CARBON CARBO CARBON
btw. did I mention carbon rods?
The same as for lead: As long concentration of the H2SO4 is not to high and the concentration of the MgSO4 not to low this will work fine. Even
stainless steel might be worth a try.
Just replentish your electrolyte!
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Organikum
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ALL CAPS
CARBON CARBON CARBON CARBO CARBON
btw. did I mention carbon rods?
The same as for lead: As long concentration of the H2SO4 is not to high and the concentration of the MgSO4 not to low this should work fine. Even
stainless steel might be worth a try.
Just replentish your electrolyte!
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Saerynide
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I was using carbon rods before
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