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vulture
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[*] posted on 6-9-2002 at 07:02
Strenght of oxidizers


As we frequently use several oxidizers, react them with eachother and synthesize them, I thought it would be useful to compile a table of strength of oxidizers.

First of all, there are a few classification problems. We could just take the redox potential and sort according to that, but that doesn't always correctly predict behaviour and also is rather confusing to work with (mmkay, this get's oxidized then that is reduced and..err. oh..or is this the oxidizer?).

Secondly, the reaction situation has to be determined. I was thinking of the strength in solution, simply by testing which oxidizer would be capable of oxidizing the other.

These are the compounds I'd like to see classified (I've classified them according to what I think, starting with the strongest):

Mn2O7
HClO4
S2O8 2-
Cr2O7 2-
MnO4 2-
ClO2 -
ClO -
ClO3 -
H2O2
ClO4 -

Remember that this is all in solution regarding cold chemical oxidation.

Waiting for your corrections/comments...




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[*] posted on 6-9-2002 at 07:03


The H2O2 should be listed above ClO3-



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[*] posted on 6-9-2002 at 14:29


You're right that different oxidizers have different behavior depending on conditions. H2O2 can serve as a reducing agent or an oxidizer, for example. We're often interested in oxidizers in high-temperature anhydrous conditions (combustion) as well as aqueous solution. Ammonium perchlorate is a much better high-temperature oxidizer than sodium hypochlorite, but sodium hypochlorite will react with many more chemicals in solution.

I think that I would add HNO3 to your list somewhere in the upper half.

I'd also add a few mild oxidizers: Cu2+, Pb4+, and MnO2. They would probably fall near the bottom of the list.

As far as your ordering goes, I think that persulfate salts are considerably less aggressive than permanganates and dichromates in aqueous solution. Also I think that chlorates are far less active than H2O2.

There are also perchromates and manganates, which are powerful oxidizers (the perchromate especially).

Somewhere on that list should go the halogens, although none of us is very likely to be using fluorine or astatine in the lab.
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[*] posted on 8-9-2002 at 01:35


persulfates are very strong oxidizers, when moist, they will spontaneously decompose into O2 with a high O3 percentage. Also, it is known that persulfate will oxidize chlorate to perchlorate. My attempts with MnO4 - to do this have failed so far.



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[*] posted on 13-10-2003 at 09:42


is there any safe synthesis of Mn2O7 ? where can i find information about it ?
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[*] posted on 13-10-2003 at 13:09


Ive heard that BiO3- is a plenty powerful oxidizing agent. My inorganic text book has this to say

"One of the few oxidizing agents even more powerful then permanganate is the bismuthate ion [BiO3]- A test for manganese (II) ion is the addition of sodium bismuthate to a sample under cold, acidic conditions. The purple permanganate ion is produced, thereby indicating the presence of manganese."

Descriptive Inorganic Chemistry [Third Edition] Geoff Rayner-Canham Tina Overton
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[*] posted on 13-10-2003 at 15:45


thats interesting (the BiO3- bit). Although it's off topic, how would I go about making it? Assuming my starting point is Bi metal?
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[*] posted on 14-10-2003 at 17:42


According to my old (1961), but very useful Textbook of Inorganic Chemistry (Partington)... On fusing Bismuth Trioxide with Potassium Hydroxide in air, a brown mass of Potassium Bismuthate, KBiO3, is formed. It is hydrolyzed by water, but with cold solutions of Manganous salts in dilute nitric acid it gives a purple solution of Permanganic Acid. So there you go.

Bismuth Trioxide, Bi2O3 is formed by heating the metal, hydroxide, basic carbonate or nitrate to redness in air. Hmm, just noticed... it also says that Bismuth Trioxide is used to produce an iridescent white glaze on porcelain. Perhaps it is available through a pottery supply company???

Not mentioned in your list, but leave us not forget the supreme oxidizing power of Xenon Difluoride!
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[*] posted on 4-1-2004 at 13:40
bismuth


You know with an ebay and all Bismuth is readily available and it is not a hazardous material. And yes it is tricky on figuring outoxidizer strength. ClO3 is stronger than H2O2 in the respect that ClO2 oxidizes H2O2 to clorous acid and oxygen gas; but peroxysulfates can oxidize chlorates to perchlorates. I always regarded peroxysulfates as hydrogen peroxide adducts. Confusing indeed.



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[*] posted on 4-1-2004 at 14:35


Quote:

Not mentioned in your list, but leave us not forget the supreme oxidizing power of Xenon Difluoride!

I always thought that the oxidizing power of Xenon Difluoride came from it releasing free fluorine in the reaction mixture. For the list, at the very top, I would just put F2 fluorine has been described as the "Tyrannosaurus Rex" of the periodic table. I mean, how else am I going to make perbromic acid?




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[*] posted on 4-1-2004 at 15:35


IIRC CoF3 decomposes to F2 and CoF2 on heating. This means that Co (III) is a stronger oxidant than F2
(Yes, I know that's blasphemous).
OTOH Co(OH)2 is oxidised by air to give Co(III) so O2 is a better oxidant than Co(III)
This means that O2 must be a stronger oxidant than F2. The trouble is that we know it isn't.
This serves to ilustrate the fact that what is a good oxidant depends on circumstances to such a great extent that putting them in order is going to be a bit of a non starter unless you use some sort of standard conditions. If you do that, you might as well use the electode potentials.
Add to this the problem of kinetic versus thermodynamic stabillity (Fe(II) perchlorate shouldn't exist) and the list won't really help very much.
BTW if you react peroxide with acetic anhydride you get peracetic acid. This will oxidise Mn(II) to permanganate, even in slightly acid conditions.
(Peracetic acid is rather unstable and I wouldn't use it if I were you)
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[*] posted on 7-1-2004 at 22:25


Quote:

Add the H2O2 to the beaker(or drop reactant into H2O2) and test for gas bubbles.
If there are any trap in a test tube and test for any explosive peroxides using a lighted splint.

Are you saying that the organic peroxides will certainly be in the gas phase with any oxygen produced? I don't think so... oxygen is the gas produced from H2O2 decomposition (assuming that's all that's occurring) and it lights a smoldering splint. I don't think that would be a good test at all considering the common production of oxygen would cause a false positive. Did you mean to say something completely different and typed out the wrong thought?




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[*] posted on 27-11-2005 at 13:05


I was looking around the internet for a table listing the electrochemical series and found one that has a number of enteries in that that would be considered extrenuous on a normal table, this one has 536 enteries on it and the top ones are whoppers such as:

XeF + e- = Xe + F- 3.4V
Cf4+ + e- = Cf3+ 3.3V

And many more interesting enteries (ferrates, fluorine/oxygen compounds...), see what I mean at:

http://www.efunda.com/materials/corrosion/electrochem_list.c...

[Edited on 11/27/2005 by BromicAcid]




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[*] posted on 27-11-2005 at 13:31


WOW Bromic:o. I have been looking for such a giant table for a long time. Thank you.

Pr4+, Tb4+ !! I gotta get me some more lanthanides:P

EDIT: AArg, I got through perhaps the first 200, and it wants me to subscribe:mad:

[Edited on 27-11-2005 by rogue chemist]




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[*] posted on 27-11-2005 at 14:14


Quote:

EDIT: AArg, I got through perhaps the first 200, and it wants me to subscribe:mad:


Yes, I was looking forward to see some exotic reducing agents when I recieved the same thing. I will add the electrochemical series listed in the CRC to Madhatters FTP when I find it. Same content, but as a PDF.

Edit: (Madhatters FTP) Upload -> CRC_SRPotentials.pdf

[Edited on 27-11-2005 by Phel]
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[*] posted on 27-11-2005 at 15:35


Quote:
AArg, I got through perhaps the first 200, and it wants me to subscribe:mad:



When you get this problem, go to BugMeNot and enter the site name. For this site (efunda) it comes up with:-
Username mrx
Password xyz

Mike.

[Edited on 27-11-2005 by Pommie]
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[*] posted on 27-11-2005 at 16:32


I had tried that already, aparently mrx dident pay for this years subscription. Oh well, you have access again in around an hour and by modifing the url you can get to the later pages. I have got to around 300 saved now.



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[*] posted on 27-11-2005 at 16:34


Hmm. Interesting that that site lists oxygen difluoride below fluorine; I'd expect it to be higher.
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[*] posted on 28-11-2005 at 09:17


I think a powerfull, possibly the strongest oxidizer might be KrF2 since the Kr-F bonds are even weaker then in elemental F2 (and are among the weakest known covalent bonds to exist).
weaker, less "exotic" (and more safe) oxidizer are perxenates: XeO4-2 (XeO3 and XeO4 are explossivly unstable). the big advantage of using them is that the byproduct is Xe, hence no need for seperation and purification of products (like H2O2 but much stronger)
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[*] posted on 28-11-2005 at 09:30


and some more on the subject...
some time ago I heard a seminar in our department and what catched my attention (between snors...) was a certain lithium complex of an organic molecule that undergo disproportionation to...
Lithium metal :o and a some other specie
the lithium precipitate as a shining miror on the flask's wall...
i.e - this molecule is a stronger reducer then metallic Li.
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[*] posted on 28-11-2005 at 11:51


" this molecule is a stronger reducer then metallic Li."
So, it's about as far off-topic as you can get.
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[*] posted on 28-11-2005 at 12:39


I have made my own classification of oxidizer in speed of reaction. Speed of reaction is not the same as strength of oxidation. E.g. persulfate is the strongest oxidizer I have, but also a rather sluggish one.

Mn2O7 (not aqueous, but very reactive)
MnO4(-)
ClO(-)
Cl2
HNO3 concentrated
H2O2
Cr2O7(2-)
Br2
H2SO4 concentrated
S2O8(2-) (sluggish but potent in aqueous media)
BrO3(-) (sluggish in aqueous media, works only in acidic media)
I2
ClO3(-) (sluggish in aqueous media, works only in acidic media)

HClO4 (hardly works as oxidizer, not at 60%, just a nice clean strong acid)
ClO4(-) (not oxidizing at all, totally inert)

So, my list is not an electrochemical series, but more like a series of observed reaction speeds. Mn2O7 is very fast acting and HClO4 (up to 60%) and ClO4(-) are so slow, that they cannot be considered oxidizers anymore.

I took some 60% HClO4 and added solid KI. This does not give any reaction (besides dissolving some KI). Even when heated close to boiling, the liquid only becomes a little yellow/brown, that's all.

With a mix of HClO4 and NaCl, only when heated to boiling, a very faint smell of chlorine can be observed. From these observations I conclude that HClO4 (at least not at 60 .. 70%) is not useful as oxidizer at all, despite all the strong stories on the Internet about the dangers of HClO4.




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[*] posted on 28-11-2005 at 12:47


Phone NASA and tell them to cancel the next shuttle- perchlorates aren't fast oxidisers any more.

There is probably less hope of getting a valid list of oxidisers (fast to slow) than there was of getting one (strong to weak).
At best you would need the pre- exponential and the activation energy terms for an Ahrenius type equation. I think that means you would need a veactor for each oxidant and I'm not sure how you could put those in order.
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[*] posted on 28-11-2005 at 13:08


unionised,
what is your problem?
have you mixed your medications today?
have'nt the nurse told you to take the blue pills?
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[*] posted on 28-11-2005 at 16:11


Quote:
Originally posted by unionised
" this molecule is a stronger reducer then metallic Li."
So, it's about as far off-topic as you can get.

Not really, given that oxidation and reduction are two sides of the same coin.
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