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Author: Subject: Stuborn MnO2
YT2095
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Stuborn MnO2

with the exception of HCl, non of the usual acids will attack it in any appreciable way.

HCl at best will dissolve a little bit of it leaving a brownish soln with loads of unreacted HCl and MnO2.

my goal is make a sulphate, a nitrate and a chloride of this metal.

at the moment the only thing that springs to mind is a Thremit reaction to obtain the metal and start from there.

but its quite crude and not very elegant, Ive no objection to doing this if its the only way, but Ide rather not.

any ideas?

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kaviaari
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YT2095
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Excellent thanks, I must have skipped right past that in the search.

the direct SO2 reaction looks kinda sexy

I think for Now, Ill put some in the crucible and roast it down to MnO and try from there, maybe give the H2O2 and H2SO4 a shot too in the morning.

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woelen

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MnO2 comes in different forms. I think you have the crystalline calcined stuff. I also have some of it and this stuff SUCKS . It is rather inert and very hard to get in solution. I could get a small amount in solution, by boiling it with concentrated HCl for 10 minutes or so, but this is horrible. Lots of HCl-fumes.

There also is a very fine amorphous powder, and that material is much more reactive. If added to HCl, it quickly dissolves, giving a very dark brown/green solution and you quickly smell the chlorine coming from the solution.

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12AX7
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Heh, if you wanted to be really roundabout about it you could fuse it with soda and decompose it in water (as sodium manganate is rather unstable in solution).

HCl tends to reduce and complex(?) with MnO2 so does a fair job, a far sight greater than sulfate, which hardly dissolves Mn(III) anyway (very low pH solutions, rapid hydrolysis). Whatever you do, you need a reducing agent in there.

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YT2095
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Woelen, I think it is exactly what youve described unfortunately

in addition, according to mt book MnO2 decomposes at 808k I roasted this stuff in the crucuble to a Much higher temp (forced air Propane) and no Green color at all. not only that but with the crucible lid taken off there was even the odd spark/flash taking place inside it!

I think this may be a Bad Product

on microscope examination it is indeed crystaline too for the most part, the Thermit reaction is becoming More and More tempting as time passes.
if I have to go this route, does anyone know how "Violent" an Alu MnO2 reaction is?
I dont want some exotic type sh!t thats going ruin the product or create annoyance/disturbance.

the H2SO4+H2O2+MnO2 reaction Does work exceptionaly well, there is little MnO2 left undisolved, there is no need for Conc reagents either (40% sulphuric to MnO2 then add 9% H2O2 dropwise).
seems a real waste of good O2 though, I think Ill get the gas syringe out when I scale it up and collect it for a rainy day

and that direct SO2 conversion is a Must Try! when Im free for a few hours

edit: Whoa! a surprise (unexpected) is that not only does the H2O2 trick work with Sulphuric , but also worked in the HCl batch that wasnt going anywhere either, its all dissolved!????

[Edited on 8-1-2007 by YT2095]

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kaviaari
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I am dealing with the same problem. I recieved about 200g of very old MnO2 from school. I assume that the reagent and bottle are from 1950's. I was thinking about converting it to manganese carbonate. 15ml of cons. hydrochlorid acid was poured on one gram of MnO2. The mixture was heated in water bath. Chlorine was released and I left the beaker sit for a week. Even after that there still was some unreacted MnO2, so I added more acid an heated it again. Didn't help at all, so I just filterated off the excess MnO2.

I poured saturated solution of sodium bicarb to acid-MnCl2-mixture. Carbon dioxide was released big time so I did the adding very slowly. Finally brown manganese carbonate started precipitating. Here is the picture of the crude product (it's wet too ).

[Edited on 8-1-2007 by kaviaari]

YT2095
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interesting notes, you were actualy lucky to even get Cl2 gas, no such thing happened here at all with this stuff, certainly not at any noticable level (and I did check for it), pity you dont still have this experiment on the go, Ide recommend adding a little H2O2 to it, its cleared mine up just great, although unlike the H2SO4, the HCl is a more foamy reaction I found.
so dropwise and stir and seems to be the best way for HCl.
although I really cannot comment as to the color, since its no longer Brown in soln but closer to clear yellow, albeit a Dull clear yellow, not at all Vivid.

[Edited on 8-1-2007 by YT2095]

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kaviaari
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 Quote: Originally posted by YT2095 interesting notes, you were actualy lucky to even get Cl2 gas, no such thing happened here at all with this stuff, certainly not at any noticable level (and I did check for it), pity you dont still have this experiment on the go, Ide recommend adding a little H2O2 to it, its cleared mine up just great, although unlike the H2SO4, the HCl is a more foamy reaction I found. so dropwise and stir and seems to be the best way for HCl. although I really cannot comment as to the color, since its no longer Brown in soln but closer to clear yellow, albeit a Dull clear yellow, not at all Vivid. [Edited on 8-1-2007 by YT2095]

I walked to lab and took out my hydrogen peroxide, hydrochloric acid and manganese dioxide and walked straight out to the night. I mixed about a half of teespoon of manganese dioxide with about 10ml of 38% hydrochloric acid. I heated up the reaction and large ammounts of chlorine was released. The smell was quite unpleasant even though I was outside. I added slowly one ml of 30% hydrogen peroxideI and saw a bit of a yellow foam forming. After 10 minutes the solution is clear and has no traces of MnO2 in it, but it is yellow, as yours. Might be due to the impurities like iron?

I am now going to add some more MnO2 to the mixture tomorrow and probably try to convert it to carbonate by adding sodium bicarb.

[Edited on 8-1-2007 by kaviaari]

YT2095
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if theres impurities, its going to be much easier to shift them when all is dissolved. at least now you have your Mn compound in soln.
from there you may work

Im pleased that the H2O2 think worked for you also in HCl, I cant be 100% certain yet as to WHY it works like it does, but I have a feeling it may be catalytic and catching the free ions as they react with the peroxide and locking them to the acid whilst fee.

Ill leave that to the experts here to establish for certain, do NOT take my hypothesis as truth!

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kaviaari
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 Quote: Originally posted by YT2095 Im pleased that the H2O2 think worked for you also in HCl, I cant be 100% certain yet as to WHY it works like it does, but I have a feeling it may be catalytic and catching the free ions as they react with the peroxide and locking them to the acid whilst fee.

MnO2+4H+2e-->Mn2+ +2H2O

H2O2-->2H+ +O2+2e

And this happens in highly acidic solutions. So H2O2 helps converting MnO2(s) to Mn2+-ions and therefore the manganese reacts way faster.

Waffles
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 Quote: Originally posted by YT2095 on microscope examination it is indeed crystaline too for the most part, the Thermit reaction is becoming More and More tempting as time passes. if I have to go this route, does anyone know how "Violent" an Alu MnO2 reaction is? I dont want some exotic type sh!t thats going ruin the product or create annoyance/disturbance.

Too violent. Example:
http://img.photobucket.com/albums/v97/iamthewaffler/science/...
This picture was taken at about 3 in the afternoon, quite sunny. The brightness of the reaction just washed out all the sunlight.
If you want to think about an aluminothermic reduction, you need to use Mn3O4

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guy
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Quote:
Originally posted by iamthewaffler
 Quote: Originally posted by YT2095 on microscope examination it is indeed crystaline too for the most part, the Thermit reaction is becoming More and More tempting as time passes. if I have to go this route, does anyone know how "Violent" an Alu MnO2 reaction is? I dont want some exotic type sh!t thats going ruin the product or create annoyance/disturbance.

Too violent. Example:
http://img.photobucket.com/albums/v97/iamthewaffler/science/...
This picture was taken at about 3 in the afternoon, quite sunny. The brightness of the reaction just washed out all the sunlight.
If you want to think about an aluminothermic reduction, you need to use Mn3O4

WOW!

chemoleo
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A way round this is to use large-grain Al, or, as waffler says, Mn3O4 which can be obtained from MnO2 by roasting. I can dig out the procedure if you wish.

PS I did this thermite too, and it was fairly vigorous. But using the same Al powder, and Fe2O3, it was equally vigorous. And we all know Fe-thermite works for preparing Fe. Thus its reaction is adjusted by grain size. CuO/Al still tops it all, it is essentially behaves like flash, and is *extremely* sensitive to flame, sparks etc. Any confinement invariably produces a loud bang and a copper cloud.

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kaviaari
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Some more notes about my experiment. Now I have added a teespoonfull of MnO2 to the mixture. I also added two milliliters of 30% hydrogen peroxide. Solution is still quite yellow. I think this is not due the impurities but due to the Mn2+-ion. Some kind of odd yellow precipitate is also formed. I added a millilter of HCl, but it is not dissolving. Well I can filterate it off. The method is very efficent and I am going to scale it up for converting all of the impure manganese dioxide to manganese chloride.

[Edited on 9-1-2007 by kaviaari]

YT2095
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wow! is right, that reaction is way out of my league for comfort and Ive a feeling that picture doesnt do it justice either, esp as you mention if WAS daylight and it looks like Night time by comparison, perhaps something scaled down to a tenth of that size as a last resort, the only Alu powder I have is 10 micron, far too fine for a "Tame" reaction.

Ive finished roasting 5g of the MnO2, and the strange part is that the powder is now Brown, and my book lists all oxides of Mn as Black with the exception of MnO and it say Green for that. brown is not mentioned anywhere?

I was intrigued as to why there were several flashes going on in the crucible also, so I put a magnet in the MnO2 I have, and a percentage of it is magnetic? so thats either the Mn metal itself not fully converted to the Oxide, OR there is an oxide of Mn that is magnetic like there is with Iron hematite.

Im beginning to question the purity of this material.

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woelen

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Mn(III) is brown in most of its compounds. You roasted the oxide and part of the Mn is converted to +3 oxidation state.

How easy can this Al/MnO2 mix be ignited? Is it simply a matter of holding the mix above a flame? Sounds interesting. I now have some German Dark Al-powder (1.5 micron particle size), so that should give a neat flash. I already tested that German Dark with KNO3/P/Al in Cl2 gas and the result is awesome (much better even than with the 40 micron Al I mentioned some time ago)! So, this definitely is something I want to try with MnO2. I have an almost unlimited supply of MnO2 from a local supplier at a price of just a few euro's per kilo, so that would be a good source for such flash experiments.

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 Quote: I added slowly one ml of 30% hydrogen peroxide I and saw a bit of a yellow foam forming. After 10 minutes the solution is clear and has no traces of MnO2 in it, but it is yellow, as yours. Might be due to the impurities like iron?

Last time I made MnCl2 from MnO2, I added 3% H2O2 to the mix after it appeared to have stopped reacting. Huge amounts of Cl2 came puffing out of the beaker almost instantly, all the rest of the MnO2 went into solution. I have to hand it to guy for recommending the H2O2 method back when I asked about it last spring. It definitely works. But watch out for the chlorine if you use HCL!

[Edited on 9-1-2007 by Hilski]
woelen

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I did the experiment with MnO2 and I'm really amazed by the powerful flash reaction. I never could imagine that this chemical would be capable of such an extreme reaction. I always thought that was something for the more well-known pyro oxidizers like KClO4, KNO3, etc.

[img]http://woelen.scheikunde.net/science/chem/exps/MnO2+Al+P/flash2.jpg[/img]

I found out that the mix gives a brilliant white flash, but it requires lightling with a hot flame. Adding just a percent or 2 of red P makes the mix much easier to ignite, while it hardly becomes less bright.

I put the result of the experiment on the web in a temporary web page. It is not yet a completed web page, I just added it to share it over here, but don't regard it as a final web page. Watch the bright flash, you can obtain from such a small amount.

http://woelen.scheikunde.net/science/chem/exps/MnO2+Al+P/ind...

EDIT: Why don't I see the image in the post?

[Edited on 9-1-07 by woelen]

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YT2095
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Woelen, Nice!

I am curious about all these reports of Cl2 being liberated here, Ive not even had a HINT of of such gas produced with my stuff, plenty O2, but not Cl?

9% H2O2
30% HCl

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woelen

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With just my MnO2 and HCl I also don't get Cl2, so we are on the same line of observations.

But when I mix in H2O2, then I get copious amounts of Cl2, and I definitely MUST do the experiment outside. Even just a spatula full of MnO2 and a few ml of the liquids produces a lot of Cl2, one 100 ml erlenmeyer, full of green gas.

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YT2095
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somethings going really wrong here then, I have all 3 mixed and not even a slight hint of chlorine?

this is in a 250ml flask filled to the 100ml line so far with a mushroom colored muddy liquid that is yellow when the muddy ppt settles, there is also metalic particles in the bottom that fiz quite a bit and are magnetic.
I add the H2O2 1 ml at a time as I dont want it to foam over the flask.
I took a sample of the yellow liquid and added it to sodium carbonate and got my light pink MnCO3 gel like ppt, so I know Somethings working, just not the Cl2 bit?

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I remember reading somewhere that Mn(SO4)2 can be obtained from MnO2 by reaction with either vapor-phase SO3 or with fuming sulfuric acid (H2S2O7), but it is very sensitive to hydrolysis (there must be no net water of reaction produced as byproduct).
woelen

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What concerns me are the metallic magnetic particles and the yellow color. I think you have a lot of impurity in one of your reagents, otherwise I cannot explain what you get. My solutions of MnO2 in H2O2/acid are colorless, Mn(2+) ion is VERY pale pink, almost colorless.

This impurity could inhibit formation of chlorine, the oxidation may go through another pathway, such that hardly any Cl2 is formed.

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YT2095
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the only listed KNOWN impurities are in the H2O2, it containd H3PO4 as a stabiliser and Phenacetin (no idea what thats for?).
now those two have never messed up a reaction for me yet.

I think its the MnO2 at fault, theres metalic parts in it, black magnetic parts in it also, IMO I dont even think it would make Technical grade!

the brown muddy ppt say a different oxidation state to me also, the MnO2 that roasted in the crucible would also make this color if I added water.

which reminds me, I just finished roasting some with powdered activated charcoal, that stuff is now REALLY Brown almost orange around the edges, and green/gray underneath the surface at the bottom of the pot, I think this stuff will probably be a little safer to use in a thermit reaction.

EDIT: as an afterthought, the H2O2 + HCl rxn is done at room temp here, no heating used at all, maybe that plays a part?

[Edited on 10-1-2007 by YT2095]

[Edited on 10-1-2007 by YT2095]

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 Sciencemadness Discussion Board » Fundamentals » Chemistry in General » Stuborn MnO2 Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues