Altreon
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Registered: 11-12-2025
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Electrolytic oleum
Hello. This is my first post on the sciencemadness forums. I sincerely apologize for any errors or previously documented information mentioned
hereafter.
In 2024 I tried electrolyzing a test tube for 2 weeks using two 0.3mm-thick and 10cm-long platinum wires. The electrolysis bubbled on both the cathode
and anode and smelled like things burnt by an ozone lamp(?). In the first day, all the brown contaminants that were in my somewhat dirty sulfuric acid
(stored in HDPE!) clumped up at the top of the liquid layer and eventually disappeared, turning the liquid from clear/brown to cloudy/white + brown
particles and finally to a clear liquid. I stopped once the electrolysis started producing a faint white smoke that didn't go away after the current
was stopped.
Unfortunately I did not recall any tests I performed on the liquid, aside from it creating a mysterious azure blue when I accidentally forgot to wash
the Pt cathode coated in NiSO4 soln. The Pt cathode had a very shiny black coating that would only go away when used as an anode in the next H2SO4
elec. run, which I suspect is the vitreous carbon that I also observed in elec. of glacial acetic acid with a few drops of H2SO4 (I could make another
post if there is interest in this).
I initially did this in an attempt to synthesize anhydrous H2S2O8 as it seemed I successfully produced some peroxide containing compound via the elec.
of 70% sulfuric acid, that didn't get destroyed by the platinum, that bubbled on cessation of elec., and bubbled harder with permanganate. It seems I
failed to account for it decomposing into H2SO4, SO3, and O2 in pure sulfuric acid.
After these promising results, I electrolyzed concentrated sulfuric acid for over a month using the same wires plus a third wire on the anode at 5A
using a 100mL ground glass bottle as a container, filled with 90mL of H2SO4. I tried 2A but the rate was abysmal and I had to heat it up because it
seemed(?) that conductivity decreased over time. After a month, the white fumes were able to escape from the ground glass joint, condensing some very
nice sulfuric acid vapors onto the immediate area around the flask. The spraying stopped after electrolysis was stopped, but smoke still emanated when
the bottle was opened.
Unfortunately again I was only able to test on this seemingly pure solution of dilute oleum once, but I remember pulling some through a pipette and
watching it fume and smoke through the air as I dropped it on a moist kitchen sink, along with adding iodine and observing the beautiful emerald green
of iodine cations only formed in such harsh dehydrating and oxidizing conditions as in oleum. By the next day the iodine solution became a regular
brown color, and I was unable to store any of the dilute oleum for testing due to personal issues.
I am posting this because I would like to hear the community's opinions on this synthesis of dilute oleum. It does not require heat and does not
require you to attend to the reaction at all. There are the obvious problems involved with obtaining Pt electrodes, and I have failed to find a
suitable metal that could survive as the cathode, and the wires cost the equivalent of $16 each, but if you can get past that, this method seems
viable for producing some (currently) unknown concentration of oleum. Even if the oleum turns out to be too dilute in the end, I am sure you could
purify and concentrate drain-cleaner sulfuric acid with this method, since it seems that the electrolysis ozonates all the organic impurities until
all you have left is clean sulfuric acid.
(For the cathodes: Ni/Cu produce a mix of H2S and SO2 along with green/voluminous black surface corrosion respectively, Mo slowly decomposes into Mo
blue above the H2SO4 surface and white milkyness below without any oleum content, while W very slowly turns brownish and turns the soln. cloudy,
though it might still produce oleum as I am currently conducting this tungsten experiment as I speak. I believe that a C cathode just crumbles while
Ag very quickly turns into white milkyness, notably unlike clear AgHSO4 soln. Ti dissolves into a hot purple soln relatively quickly. The most
resistant metal so far aside from Pt is W.)
[Edited on 13-12-2025 by Altreon]
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Altreon
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Registered: 11-12-2025
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Tungsten is not (or does not appear to be) a suitable electrode material. Similar to molybdenum, it looks very promising with a steady flow of H2, but
the cloudy acid produced is seemingly about as concentrated as the original acid because of its reaction with wood.
It seems Pt for both the cathode and anode is the only way this can work. Maybe Au could work for the cathode (anodic Au dissolves to form a purple
soln. in dilute sulfuric acid) and PbO2 could work for the anode though I've never seen those electrodes.
Edit: the sulfuric acid formed from W electrolysis reacts especially violently with water. The sulfuric acid had already cooled down to room temp.
Nothing precipitated, so I'm not sure if a compound without tungsten (i.e. oleum) actually did form and I did not electrolyze for long enough.
[Edited on 16-12-2025 by Altreon]
[Edited on 17-12-2025 by Altreon]
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Mister Double U
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Registered: 21-2-2025
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Hello Altreon,
Regarding a Tungsten cathode: Do you smell any SO2 coming from the cathode? If not, you are decomposing water and thus concentrating the acid.
After running your cell for some time you could dilute your acid down and titrate to determine the concentration. If you compare that to the original
acid you will see if you concentrated the acid (you would need to draw a same weight sample from both groups).
If you have a big enough sample you could do it with a known molarity Sodium Bicarbonate solution in lieu of a ph indicator. You are done when
bubbling ends.
That might be more reliable than the wood test.
Best greetings!
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Altreon
Harmless
Posts: 3
Registered: 11-12-2025
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Mood: oxidizing
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There was no detectable amount of SO2 coming from the W cathode, but I can't consider this as reliable because Mo works the same way while a nearly
invisible reaction occurs with the sulfuric acid, which may or may not dilute it.
I spilled all the electrolyzed sulfuric acid, which is why I compared it with its rxn. with wood. I will repeat this electrolysis with more sulfuric
acid and try to titrate it this time.
On a different note, do you know of any ways to qualitatively determine if W is present in soln that doesn't involve thiocyanates?
[Edited on 17-12-2025 by Altreon]
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