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chemoleo
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[*] posted on 19-8-2004 at 18:09


Ok, I don't know about KMnO4 (I guess we have to try!) but I know about H2O2 - when I added it to Pb(OH)2 I got PbO (I posted that somewhere), nicely yellow, and MASSES of H2O2 - in fact O2 evolution happened so fast that it scared the s*** out of me because I thought the lab smoke detector might go off!
So PbO--> PbO2 via H2O2 is a no no!

(i.e. it DOESN'T work, under those conditions, all you get is PbO and lots of oxygen - i.e. JohnWW seems correct about hte autocatalytic decomposition of H2O2)

[Edited on 20-8-2004 by chemoleo]




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[*] posted on 19-8-2004 at 20:12


JohnWW, add Mellor to your list of those wrong as well.

chemoleo, the Pb3O4 equations were not made up. Whether this is the case or not, I can only put my trust in authors who say so. This and the PbO>PbO2 was an attempt to find the relevance to the thread subject, not PbO.

I should add that in the old days it seems that chlorates were favored over nitrates for dioxide production.

chemoleo made a nice statement about conditions. I never or at least rarely say that something doesn't work. IMHO it's a matter of finding the correct conditions to make something work.

I'll try both H2O2 and KMnO4 this week, but I have to buy some Pb first, dissolve in HNO3... so it'll be a couple days at least. Not that I have super powers, but I'm curious now, and might be able to add something.

So that I might have something marginally constructive to add, I badly translated and abridged the synthesis in Brauer. Trust at your own risk:

2Pb(CH3CO2)2-3H2O + Ca(OCl)2 + 4NaOH->2 PbO2 + CaCl2 + 4 CH3CO2Na + 8 H2O

20 g Pb acetate trihydrate in 50 ml water is mixed with a solution of 10g NaOH in 90 ml H2O. 14 g Ca(OCl)2 (70-80% available Cl) is added to 200 ml H2O. This is filtered and 80 ml of the filtrate is added slowly with stirring to the Pb solution. This is boiled for a few minutes and PbO2 separates. More of the hypochlorite is added, 10 ml at a time, for as long as more precipitate forms.

The precipitate is washed by stirring and decantation several times with water, once with 50 ml 3N HNO3, hot water several times, filtered and dried in a vacuum desiccator over P2O5, but is not anhydrous without heating to 160C in a current of O2.

Yield ~85%

But they prefer adding water to the tetraacetate. More active for work with organics, they say. Easier, obviously, though they use a centrifuge.
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[*] posted on 20-8-2004 at 11:23


Tried the KMnO4 oxidation procedure right today. I tried both neutral and alkaline permanganate as reagents. (I also tried the acid permanganate but right then I remebered that insoluble lead (II) sulfate would form).

In both the alkaline and neutral permanganates a brown ppt was obtained, with a slightly larger amount in the case of the alkaline soln. The ppt did not have the same colour as the real PbO2. Following the formation of the ppt I tried a couple of test on it. It resulted as a mixture of both some lead compound, which might be PbO or most probably PbO2 with some Manganese compound, most probably MnO2.

I will try this again in case some manganate impurities in the ppt gave the 'pinkish' colouration on reacting with sulphuric acid, but I doubt it. I think the synth with Calcium hypochlorite is the best.

Edit: Typo

[Edited on 20-8-2004 by Esplosivo]




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[*] posted on 20-8-2004 at 13:15


That brown precipitate would be most likely MnO2, produced by the autodecomposition of MnO4-.

John W.
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[*] posted on 24-8-2004 at 08:37


I produced my first largish batch of PbO2 today using the method named by Polverone, ie using solid Ca(OCl)2. The precipitate formed was very easy to filter, even with cheap coffee filters! This is probably the most viable way to produce home-made PbO2. I didn't basify the solution though. That could have increased the yield, although I am quite sattisfied with the batch I obtained from less than 100ml of dilute solution.

All is going well for the construction of the chlorate/perchlorate cell.




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[*] posted on 27-8-2004 at 14:17


Quote:

McAlpine and Soule are definitely WRONG about KMnO4 oxidizing Pb(II) to PbO2 in alkaline solution. As for H2O2, I suspect they are wrong again, because even small amounts of heavy metals merely catalyse the autodecomposition of H2O2 with the evolution of oxygen. At best, it would take an enormous excess of H2O2.


I don't know if anyone believed this or not, but I'll rant just in case. I suggested that he check the literature, and he calls the literature BS. I checked the literature and found journal refs to PbO2 from:
alkaline Pb acetate and H2O2
alkaline Pb nitrate and H2O2 (quite pure, btw)
alkaline PbO and KMnO4
But one of Rhodium's funnier lines applies here: "However, to obscure their discovery as much as possible for the rest of the world, they encrypted their findings by publishing it in french (PGP was not available at the time)." And if not French, German. Unfortunately the volume of Mellor that covers PbO2 (vol 7, pp. 681-687) is the only one that the library doesn't own, and his "Modern Inorganic Chemistry" is only so helpful here.

Authors such as McAlpine and Soule (the excellent "Prescott and Johnson's Qualitative Chemical Analysis";), the writers for Mellor - and farther back, Thorpe, Roscoe and Schorlemmer, and Watts - go by and reference actual papers published in respected journals. When something is questionable they find a way to say so. They state facts that are known, not make things up.

Those who disagree should publish their own book to counter the BS artists such as Inorganic Syntheses: "Hypochlorite is the most commonly used oxidant, but permanganate, sodium peroxide, ferricyanide, and many other oxidizing agents can be used." However, in order to get published, one would have to do better than mumble something about oxidation of Mn(II), something which happens in acid, and in any case I don't see how it applies here. So, elaborate if you can, please.

OK then - first I dissolved some Pb in dilute HNO3. Used my high-tech sublimation apparatus for this - a pint beer glass sealed with a RBF, and a "warm"plate. But the last of the lead was slow to dissolve. I got impatient so I converted it all to sulfate and carbonate. I wanted the sulfate to test the easiness of conversion to PbO by fusion with Na2CO3, and will try something like US3644090.

The carbonate was converted by heat to a dull flowerpot-colored oxide, and some of this was heated more strongly to a bright dark orange oxide that was red-violet when hot. Heating the bright oxide in vinegar gave PbO2 as a dark brown precipitate and half the Pb as soluble acetate, which was precipitated as the sulfate with H2SO4.

The experiment with the lower oxide and H2O2 was first tried at perhaps 50C with a 25% excess of conc. NaOH. Dropwise addition of unheated H2O2 in concentrations between 10 and 30% gave an immediate formation of brown sludge at the site of reaction, but disappeared no matter how much more peroxide was added and at what rate. The H2O2 was made by evaporation of grocery store 3% and had a pH of 3.38. Should have added some base to it before addition.

Repeating this at nearly boiling temps was dramatically different, and dark brown PbO2 formed and remained easily. Not much H2O2 was required. HCl was added with the formation of white PbCl2 and Cl2.

The experiment with KMnO4 was done next, also with a 25% excess of oxidant and base. This was done at boiling, and an unheated satd soln of KMnO4 was added dropwise. There certainly was no "autodecomposition" of the KMnO4, and the excess was decanted off and the precipitate washed many times. It gave the sensitive color test for Mn, by fusion with NaOH and KNO3 in a porcelain crucible. It gave Cl2 and white precipitate with HCl. MnCl2 is quite soluble, and the filtrate was chlorine green-yellow.
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thumbup.gif posted on 9-9-2004 at 13:30
1st batch of PbO2


This was made from:

1) mixing bleach with a lump of PbAc2

2) letting it react at a 75 degrees C oven for an hour

3) letting it sit overnight, then filtering through a coffee filter

4) letting the filter dry, then scraping it out

No purification has been done, but I'm now confident that household bleach (mix of NaOCl and NaOH) <i>can</i> indeed be used in this process.

EDIT: I know the camera makes it look black, but it's really dark brown -- camera does bad job with big light contrasts and bad lighting.

I managed to get hold of 5 litres of bleach today (some sort of outdoor furniture cleaner / algae killer) and will begin preparing a proper PbO<SUB>2</SUB> batch shortly.

This is fun!

[Edited on 2004-9-10 by axehandle]




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[*] posted on 9-9-2004 at 13:40


That sounds OK. High-valent compounds of other metals like Fe(VI) and Mn(VII) , in solution as anions, can be obtained the same way, viz. with household bleach (alkaline NaOCl), or with Cl2 in alkaline solution.

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[*] posted on 9-9-2004 at 14:21


Well, it's an amazing synth! No suspicious things needed, only pottery pigment, metallic lead, vinegar and bleach!

Possession of lead salts/compounds here basically carries a caning sentence so they are impossible to get, for any price.

However....:

1) Copper carbonate: cheap
2) Vinegar: cheap
3) Lead: almost free
4) Bleach: cheap
5) Look on the face of government chemical dept.: priceless

Guess I should send them some :D

[Edited on 2004-9-10 by axehandle]

EDIT: I'd really like to do this using a centrifuge -- at this rate the sedimentation will take days done properly sigh...


[Edited on 2004-9-11 by axehandle]




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[*] posted on 16-9-2004 at 20:39


I just implemented an improvement of the process that's not really obvious: I dumped in an aquarium water pump (the submergable kind) in my 2nd copper acetate / Pb vat (without any hose attached) to speed up the process. Easy way to "stir" the fluid.

My washing / sedimentation of the first batch of PbO<SUB>2</SUB> is going on nicely, albeit very sloooowly. Takes several hours for the PbO<SUB>2</SUB> to sink down to half the height. Wishing I had a centrifuge. Wouldn't be that hard to build one... hmm.

Also wishing I hadn't cheaped out and bought the least expensive NaClO I could find... damned thing contains some kind of soap or detergent that makes bubbles, plus it takes a lot of water to wash away... still, time is cheap I suppose.

EDIT: The pump was a REALLY good idea! If I didn't know better I'd say that stirring the thing would make it possible for the reaction to be finished in a couple of days as opposed to a couple of weeks! I dumped it in a couple of hours ago and copper is precipitating visibly on the lead!



[Edited on 2004-9-17 by axehandle]




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[*] posted on 17-9-2004 at 09:44
Illegal?


Quote:
Originally posted by axehandle
I had 5 litres of 30% HCl and decided to make some PbCl2 just because possession of lead salts is illegal here.


What are you talking about? It's not illegal to possess Lead salts! What you can't do is using certain lead compounds for products for selling to the public!!!! PbCl2 isn't even included in the restricted compounds database at Kemikalieinspektionen.
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[*] posted on 17-9-2004 at 10:51


Are you telling me that the chem supplier I contacted (Svenska Kemi) are so unwilling to make money that they lied to me about the legality of selling / buying lead compounds?

[Edited on 2004-9-17 by axehandle]




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[*] posted on 17-9-2004 at 11:17
VERY weird


Can anyone explain this:

(I've done the "let sink down to half the height then pour off water then add water" cycle about 10 times without this happening!!!)


[Edited on 2004-9-17 by axehandle]

pbo2_layers.jpg - 30kB




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[*] posted on 17-9-2004 at 12:52


Axehandle,

I don't know about Svenska Kemi, but from what I can see from their web site, it seems like they are dealing with "consumers" directly (18 years limit for buying Iron chloride).

I've personally never had any problems buying chemicals. Though I have my privately owned company "Hardsoft Electronics" it's main business is electronics.

I usually buy ACROS chemicals, sold by Bergman-Labora, but they also sell Fisher. 250g PbCl2 costs about 210SEK (22.1 EUR).

I think I now know why you were refused to buy! All lead compounds are reproductive toxins which are allowed for professional use only. If they suspect you'll have it for personal use THEY would be violating the law!!!! But as I wrote it's not illegal to possess the substance.

[Edited on 17-9-2004 by akre]
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[*] posted on 18-9-2004 at 08:43


*grumbles irritatedly* fascist regulations.... oh how I hate this country.... I should poison the city water supply just to show them...

Aaanyway, I have made some observations during my painstakingly slow decanting process. The major one is that it was really stupid to use NaClO/NaOH solution with detergent/soap in it for two reasons; first of all it's less viscous than desirable making the sedimentation process slower, secondly it takes forever to get rid of the detergent.

I've decanted about 20 times already, still there is foam forming when adding water.

A minor observation is that the speed of sedimentation increases with each decantation -- I'm ascribing this to the PbO<SUB>2</SUB> blobs/conglomerats becoming larger over time, thus settling easier, like rocks sinking in water slowly if they're very small than if larger (can't explain this phenomenon though)... this is guessing and I'll probably get flamed to a crisp.

Thirdly, the circulation pump I added to my batch of PbAc2 in progress is doing its job admirably. I think it's safe to say that it lessens the required time for the copper acetate --> lead acetate step to less than a week.




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[*] posted on 18-9-2004 at 12:12
PbO2


Axehandle, I'm sorry that I didn't send that centrifuge to you. Sounds
like you could have really used it ! I'm also sorry that you have to put
up with bureaucratic wankers in your country ! I bought my PbO2 right
off the net ! Too many jackasses running our governments(mine included)
these days !




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[*] posted on 18-9-2004 at 14:44


A centrifuge would have been lovely for this process. I think half of the PbO<SUB>2</SUB> has been lost in the repeated decanting process, and all the polluted water that's gone down the drain (literally) has more than negated the environmental gains the bureaucrats *think* their sales ban has accomplished. I think this goes for a lot of bans -- they don't really deter determined people like me, but are more of a feel-good measure for the powers that be...

I think I've gotten rid of all the detergent now -- I just turned on the hotplate to boil it in. I'm excited to see what my yield is...

EDIT: Arrrrgghhh!!!!!!!! The damned thing flash boils! And I don't want to soil another borosilicate bowl... have to evaporate at a lower temperature, sigh.


[Edited on 2004-9-19 by axehandle]




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[*] posted on 18-9-2004 at 18:34


Holy sh$t! You dumped the wash water down the drain?!? When the water treatment facility sees the increase in wastewater lead contamination they're going to look for the source. I would strongly suggest dumping the wastewater from your experiments somewhere other than your municipal water supply.

It's ironic that this is precisely the reason why soluble lead salts are not sold to the general public.
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[*] posted on 18-9-2004 at 18:47


PbO<SUB>2</SUB> isn't water soluble and besides I doubt a couple of grams would raise many eyebrows --- I'm fairly sure all the people emptying old car batteries in the drains far outscore my very small "contribution".

If this was more than a small test batch I would have dumped the waste water in my toxic waste bin instead.

[Edited on 2004-9-19 by axehandle]




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[*] posted on 18-9-2004 at 19:37
Alternative route PbAc2 --&raquo; PbO2


I just conducted a small electrochemical experiment:

Approximately 10g of PbAc<SUB>2</SUB> was dissolved in 300 ml of hot tap water. Two titanium strips approximately 6x100x1 mm respectively were submersed in the solution, approximately 7cm apart and connected to the +5V and GND lines of a 300W ATX PSU. The cell was left running for 5 minutes.

Result: Metallic lead was formed at the cathode in needle-like protrusions which fell off when the cathode was disturbed; the anode was covered with a dark brown substance which I will assume being PbO<SUB>2</SUB>. It was easy to scrape off with a knife, proving that is doesn't adhere to titanium (which is obviously an advantage in this synthesis).

Conclusion: This is a workable alternate route to PbO<SUB>2</SUB> from PbAc<SUB>2</SUB>.

:)



And here, observe the needle-like solid lead:


[Edited on 2004-9-19 by axehandle]




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[*] posted on 19-9-2004 at 14:18


I shouldn't have evaporated the water on a hotplate -- damned PbO<SUB>2</SUB> decomposed partly to Pb<SUB>3</SUB>O<SUB>4</SUB> (?)...

So now I have to do it all over again. This time I'm getting <i>pure</i> NaOCl though, not that soap-ridden crap.

But I <i>did</i> manage to coax 152g of PbO<SUB>2</SUB> from a new (as in never acid-filled) motorcycle battery, so <b>anode, here I come!</b>

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[*] posted on 19-9-2004 at 18:15


Hey axehandle,
Interesting you've gone roughly the same route as me. Though I think you'd be better off using pool chlorine instead of bleach. It's easier to tell what you're buying. With Ca(OCl)2, I had no probs collecting the PbO2, just like Esplosivo. Only took several minutes to settle after each wash, and produced an easily filtered ppt. Also, to speed up the Cu(Ac)2 --> Pb(Ac)2, I concentrated (on steam bath) the copper acetate down about half its volume. Don't know if this causes any breakdown.

Tell me, how are you attempting your anode with the battery PbO2? I have heard of people trying this but the electrodes don't seem to last much better than carbon rods for perchlorate production. Are you going to use it as is, or incorporate it in a binder like you first said?

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[*] posted on 19-9-2004 at 19:57


Well, bleach works, but I stupidly used some kind of outdoor furniture cleaner containing soap, NaOH and NaOCl. The soap was the problem -- totally impossible to get rid of. I'm getting pure bleach tomorrow.

The anode manufacturing idea is this:

1) Smear THF or PVC glue containing THF on the surface of the plastic substrate.

2) Rub it in powdered PbO<SUB>2</SUB>.

3) Let dry. Gently remove excess PbO<SUB>2</SUB>.

4) Submerge a part of the PbO<SUB>2</SUB> coated substrate in a plating tank and plate that part (this will be the "connection" part of the anode).

5) Turn it and plate the rest, taking care that the areas overlap.

My plating bath will be a water solution of PbAc<SUB>2</SUB>, slightly acidified with HAc.


[Edited on 2004-9-20 by axehandle]




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[*] posted on 19-9-2004 at 22:26


Axehandle, I've been tinkering a fair bit with this Pb(Ac)2 method.

For my test anode, I cut a strip of pvc from some pipe (got heaps of it), cleaned it with pvc primer and coated the convex side in everyday pvc glue. Then I just pressed/rolled it in the PbO2 powder. It sticks very well, although I didn't use enough glue and it's a bit patchy. But it does conduct.


As for the plating solution, I'm not sure how much luck you'll have that way. I certainly haven't been successful.
At http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/... he says,
Quote:

The lead acetate should be at a concentration of 0.5 mol/dm^3, + acetic acid and the current density fairly low.
I'm not sure if he got the information straight from the refs he cites. I think if the bath is not acidic enough, too much lead is deposited on the cathode. After much searching, I found an interesting article on anode prep. :
Quote:

Lead acetate (100g) was dissolved in 0.5 M acetic acid solution. A platinum anode and lead cathode were suspended in the solution and a current of density 1.0 mA cm-2 was passed.
Interesting that vinegar is about 0.5 M, hey :cool: So I've spent the last couple of weeks making some solid Pb(Ac)2. You can't evaporate the solution too quick as it decomposes at 100 deg C.

Hope this helps.
janger

[Edited on 20-9-2004 by janger]
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[*] posted on 21-9-2004 at 17:49
My steaming vat of poison


Not steaming, actually, but it sounded more dramatic that way. Here's a picture of my 2nd run, making PbAc<SUB>2</SUB>.

The thing under the surface to the left is a sheet of Pb, the ring in the back (and at the front, although you can see only the top) was a disc of lead I cast in an old cooking pot lid. The circuference was thickest, and only a ring remains.

The black device in the middle is a submersible aquarium water pump to improve the circulation.

This run is complete, the liquid should now be almost pure aqueous solution of PbAc<SUB>2</SUB>.

Look at all copper fragment sludge at the bottom --- yuck!

EDIT: More info... total volume is close to 10 litres, I used 500g of copper carbonate and the stochiometrically necessary amount of HAc times ~1.5, don't remember the exact amount... Right now I'm filtering the liquid through carbon, then it's boiling time.


[Edited on 2004-9-22 by axehandle]

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