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Author: Subject: MgSO4 --> H2SO4
Saerynide
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[*] posted on 24-3-2004 at 02:14
MgSO4 --> H2SO4


AHHH!!!! STUPID NO SUBJECT THING!!! I have to retype it all now!!! I spent 1/2 hour typing that!!!! :mad:

Anyways....

There seems to be a "sulfuric acid production race" going on here, with axehandle and his catalyst + burner, darkflame with his copper sulfate and me with electrolysis of MgSO4 (yes, im still working on that. Im a stubborn girl:)). I think I should start a new thread on this, because the old Copper Sulfate one was getting messy and deviating away from CuSO4 :D

I attempted again to separate MgSO4 into H2SO4 and Mg(OH)2. I finally got some *real* carbon rods from D cells (not using those crappy pencil leads anymore :D) and I replaced the papertowel salt bridge with a pvc tube to reduce all possibilities of contamination. A 30% (by wieght) MgSO4 solution was divided evenly into 2 containers and connected by the pvc tube and electrolyzed over night.

I woke up this morning and found that the anolyte was orange/amber AGAIN!! The catholyte seemed to be coming out ok like Mg(OH)2 was forming. Last time, this happened, we assumed it was iron. But this time, I am absolutely sure there was no ferrous materials in the cell. I had only glass containers, a pvc tube, carbon rods and solder (tin+lead) wires connected to the rods. I even wrapped the wired parts of the rods in tape to keep them dry. The wires also did not look corroded at all.







The only possibility of contamination would be from the solder wires I guess. I suppose I could try using copper wires hooked up the same way and see if the solution goes blue/green.

I am extremely confused now. Im not as into getting my H2SO4 now than I am in to finding out what this mysterious contaminant is. Its bugging the crap outta me!! Unfortunately, I do not have any NaOH, so I can't mix it with the anolyte to test for iron :(

Any ideas?

Edit: Filling a salt bridge is a REAL PAIN!! :mad:


Edit2: Stupid Tripod.....

[Edited on 25-3-2004 by Saerynide]

[Edited on 25-3-2004 by Saerynide]
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axehandle
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[*] posted on 24-3-2004 at 06:37


If it is the solder, you could do as I did when trying to electrolyse FeSO4:

Have the connection wires be normal copper wires, stripped about 10mm, going to the electrodes through pvc tubes that barely slip over the end of the carbon rod, holding the copper wire firmly against the carbon rod as well as providing an airtight seal.

I'm sorry I don't have any pictures, I dismantled the electrodes after my spectacular failure (using a KNO3 based saltbridge made of paper towel pumping full bridge rectified mains 220V at ~10A through the towel, setting it on fire...)

PM me if you don't get what I mean and I'll draw you a picture, it's kind of hard to explain.

Edit: Pssssst...: This is a cleaner way of connecting the ATX PSU, it allows you to use multiple cells and higher currents (forces you to cut off the ATX mobo connector though):




Edit: Found the anode! Lousy pic quality, but:




[Edited on 2004-3-24 by axehandle]

[Edited on 2004-3-24 by axehandle]

[Edited on 2004-3-24 by axehandle]

[Edited on 2004-3-24 by axehandle]




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[*] posted on 24-3-2004 at 12:53


Here's a shot in the dark: that brown solution reminds me of what I get when I dissolve MnO2 in HCl. Since your electrodes came from a battery, is it possible that they are contaminated with manganese dioxide?

Does anybody do arc welding in Singapore? A place that sells welding supplies should sell carbon "gouging rods" that are cheap, clean, and designed to be used as electrodes (you may have to peel off the copper sheath though).

Edit: you should try to see if you can precipitate that brown junk. Try adding sodium carbonate and simmering it down. If it's coming from a metal salt, it should precipitate at some point. Then you might be able to figure out what's causing the discoloration.

[Edited on 3-24-2004 by Polverone]




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[*] posted on 24-3-2004 at 16:15


Good idea, Saerynide - using the PVC pipe for a bridge vs using a paper towel. I assume you filled it with the same solution as in the two jars?

I really have no idea why the anode side turned brown. Are you using epsom salts for MgSO4? That should be pretty darn pure. You got exactly the same results using a paper towel and pencil leads? That would rule out contamination from the PVC and carbon rods.

Can you test your H2SO4 by adding a small amount of it to some baking soda and seeing how vigorous of a reaction you get?
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[*] posted on 24-3-2004 at 20:02


Yeah I filled the pvc tube with the same solution in the jars.

Im out of baking soda now. I guess I'll try to run out at get some later today. To test for iron, I think I'll add vinegar to a bit of the solution and see if I get red insoluble ferric acetate. <-- Merk index is so useful :D
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[*] posted on 25-3-2004 at 02:01


This idea is soooo good. Anyway, i was with my separation of two soluble salts(CuSO4 and magnesium ethanoate)

I am going to try this out too as and when i have free time. The problem right now is that i cannot find graphite rods. Chemicals and equipment are pretty limited in Singapore. All we have is a homefix store and a pharmacy that caters to our health. I have got two choices: get carbon rods from batteries or buy those kind of charcoal drawing pencils, and try to get the leads out(i dun'y really know how:( )

As for the steel cathode, i am hoping to use a stainless steel bowl and connect this to wire. Is it ok to do so?


I also intend to do the flower pot method during the June holidays. Instead of using lead cathodes, can i use steel or carbon?

oh ya, Saerynide, could you post the pics again? The pics dun seem to be able to load correctly

[Edited on 25-3-2004 by darkflame89]




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Saerynide
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[*] posted on 25-3-2004 at 02:36


I tried charcoal pencils. They disintegrated really fast under high current or high voltage :( So I went for batteries. They seem to hold quite well (so far).

Yeah you can use carbon instead of lead, unless there's some strange mystical power of lead that I dont know of :o Stainless steel works too.

As for your stainless steel bowl, that sounds like a very good idea. I think Ill try it on my next run :D Thanks.
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[*] posted on 25-3-2004 at 19:51


Ok, I tried adding vinegar with no luck :( I did not get any precipitate at all. Maybe it's because the H2SO4 in there keeps the ferric acetate dissolved, preventing it from precipitating?

Im heading out now on bike to get some baking soda to test the strength of the acid. :D

[Edited on 26-3-2004 by Saerynide]
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[*] posted on 26-3-2004 at 04:25


Ok. i bought my box of Epsom salts. I am so happy.:D Also bought 2 D batteries so that i can get the carbon electrodes.

Anyway, your brown solution looked like Fe(OH)3 to me...

Edit: Ok, not iron hydroxide as it is insoluble. Maybe some other iron (III) compunds..

[Edited on 26-3-2004 by darkflame89]




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Saerynide
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[*] posted on 26-3-2004 at 04:33


Fe(OH)3 is insoluble in water. I think it looks like FeCl3.

I highly doubt it FeCl3 though, the only anion in there should be SO4-, unless... the tap water was *that* impure?? (I used tap water on this try because I didnt feel like wasting dH2O on the first test run :P)
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[*] posted on 26-3-2004 at 04:39


How and what did you wrap your your cathode?



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Saerynide
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[*] posted on 26-3-2004 at 06:42


I wrapped them with clear mover's tape, but don't do that - it doesnt work too well. I suggest several layers of rubber electricians tape instead. I used that under water a few times and it kept stuff dry :D

I still havent gotten around to building my plastic-tube protected anode yet. I'll try doing it tonight and get something posted by tomorrow :D
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[*] posted on 26-3-2004 at 09:18


To protect the electrical connections between the electrode and connecting copper wire, I generally coil a length of the (stripped) copper wire around the electrode, wrap it with a few layers of tape, and then melt the tape so that it can fill in the spaces and make the connections air-tight. Unfortunately, this makes it kind of sticky, but an additional layer of tape makes handling easier.
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[*] posted on 26-3-2004 at 10:06
Cl2 precense in the tap water.


Many water purification plants (of older design) add Cl2 to the water to kill microorganisms. That may be where the Cl is coming from.

Just remembered it.

The MgSO4 could have a very slight contamination of FeSO4, as well. That would account for the iron.

As well, the water pipes in your house are possibly made of iron. That's another source. Can't think of anything else now...

But it sure <b>looks</b> like FeCl3.


[Edited on 2004-3-26 by axehandle]

[Edited on 2004-3-26 by axehandle]

[Edited on 2004-3-26 by axehandle]




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Saerynide
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[*] posted on 26-3-2004 at 11:41


Wow, Im not half bad at recognizing common chemicals :D Hehehehehe...

Thanks for those suggestions. They really helped put all the pieces together :)

Anyways, tomorow morning, I'll do the second run,with distilled water instead and with my new protected electrodes (if theyre dry by then).

If there's still any contamination... then, I'll be damned and its coming from the MgSO4 :o

Must head to bed now, its 3:40 am :D
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[*] posted on 26-3-2004 at 16:43


Quote:
Originally posted by Saerynide
Ok, I tried adding vinegar with no luck :( I did not get any precipitate at all. Maybe it's because the H2SO4 in there keeps the ferric acetate dissolved, preventing it from precipitating?

Try adding NaOH, or Na2CO3 to see if iron hydroxide or iron carbonate precipitate.
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[*] posted on 26-3-2004 at 17:54


btw. Saerynide - dont you have a "back" key on your keyboard? Because of retyping everything.....
Works everytime for me.

Also the browser might have such fancy buttons with meaningless arrows - at least mine has.




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Saerynide
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[*] posted on 26-3-2004 at 19:51


Those dont give you back what you typed :( They just reload the page.



[Edited on 27-3-2004 by Saerynide]
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[*] posted on 26-3-2004 at 21:18


Oh! Mine gives me back what I typed. Mabe its because I use OPERA? :o



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[*] posted on 26-3-2004 at 21:28
Browser Cache


You can set the size of your browser cache in your tools options. When you hit back and it reloads the page, this is because your browser is not caching the previous page. Try increasing your browser cache by 10MB to fix the issue.
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Saerynide
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[*] posted on 27-3-2004 at 00:12


Blah! I have silicone all over my hands from doing the final sealing on my protected electrodes, so im typing with 3 fingers and its hard :mad:

I added the baking soda to the contaminated solution til slightly over saturation, it fizzed alot (there is H2SO4 :D) but, I got no iron carbonate precipitate. The excess soda sat at the bottom, and the solution stayed brown, but it got lighter in colour + murkier.

I just checked the Merck index, and it says that ferrous carbonate is soluble in CO2 saturated water..... So maybe there was FeCO3,but it stayed dissolved? I didnt know this before, so i dumped the whole thing down the fscking drain instead of leaving it to settle out!!!! :mad:

Now we'll never know, and it's all my fault :(
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[*] posted on 27-3-2004 at 21:49


OK, I need to sort this out; I'm new to electrochemistry, and i feel that electrolysis has a lot of potential to produce all kinds of acids, bases, and salts that i need.

In this case, at the cathode side, H+ ions and Mg2+ ions are present in the water. Mg(OH)2 is formed because of the discharge of hydrogen gas. Which leaves the hydroxide ions behind. This then reacts with the magnesium ions to form Mg(OH)2. At the anode side, the copper anode(if i use one) will dissolve to form copper sulphate. Correct??

Therefore, in such a setup, i can produce a base or alkali at the cathose side, and produce salt(if i use a active electrode) or acid(if i use a inert electrode) at the anode. Therefore i can produce all sorts of chemicals by this woderful method!:D




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[*] posted on 27-3-2004 at 23:09


Saerynide, on adding NaHCO3 you said that no precipitate of any kind was formed?! We can therefore exclude the fact that the salt was an iron (III) since that gives a rust brown ppt of iron (III) hydroxide (since Iron (III) carbonate is unstable and decomposes on formation). We can also exclude any Iron (II) Carbonate forming, which is a dirty green precipitate.

I doubt that the fact that carbon dioxide might increase the solution of iron (II) carbonate. On the contrary. The CO2 should reduce the solubility because of the 'common ion effect' on a slightly soluble compound. Even if true, the amount of iron (II) carbonate produced would still be insoluble in water, there would be too much of it. Next time boil the water after adding NaHCO3 to remove any CO2 gas dissolved.

Better still, next time ask for some better and more accurate qualitative tests. It would help you to know what is going wrong in that cell.
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Saerynide
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[*] posted on 28-3-2004 at 00:17


Darkflame, it should work, and does for most people. But the last time I tried to get CuSO4 like that, it didnt work. I dont know why but I just got a crapload of light blue copper hydroxide precipitate :( Maybe you'll have some luck or maybe I just messed up :D Tell me how it goes if you try it :)

Esplosivo, next time I get such a contamination, I'll be sure to:
1) not chuck the solution after the test
2) take a picture after the test
3) boil the solution
4) ask for more tests

If only I had NaOH :mad:

Oh well, Im setting up the second run now. Hopefully, we wont need to resort to the above 4 resolutions :D

Edit: Here's my new pvc protected electrodes. They're gonna be used for the HCl/NaOH cell Im planning on making this summer too :D



[Edited on 28-3-2004 by Saerynide]

[Edited on 28-3-2004 by Saerynide]
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[*] posted on 28-3-2004 at 04:47


You got copper hydroxide... Well, i tried the electrolysis of salt water( not really concentrated) with copper electrodes. I did not separate the solution into 2 bowls. What i got was a green insoluble solid which i think was copper hydroxide. I am quite sure it is copper hydroxide, cause the last time i reacted NaOH and CuSO4 i got a green solid too.

That is why i wanted to make the electrochemical reactions at the 2 half cells..




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