# suylfuric acid stuff

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i went over to my friends house, and he added sulfuric acid to potassium permanganate (i dont know if it was accident or purposely) but it turned liek green. THen when he dripped liek a drop of ethanol on it like popped and cught fire- like it lit instantly on contact. why did it do that and what happened?

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he made permanganic anhydride, which oxidized the ethanol

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wat would the formula for that be?

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Mn2O7

i dont suggest you produce it unless you plan on using it soon; it's unstable and decomposes readily yielding ozone. in fact, i wouldnt suggest anybody keep any sample of it for more than 24 hours

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Dilute solutions are often used in organic chem to oxidise Org compounds, that and Potassium Dichromate, its a usefull tool. but as mentioned, its not worth keeping or using as a concentrate, Total Waste of Time and Chems.

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well, dilute solutions of permanganic anhydride would be permanganic acid, which is significantly less scary.

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Potassium Dichromate, it`s a usefull tool. but

it's also carcinogenic, so don't ever touch it without gloves or protection. Especially potassium dichromate solutions.

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Yeah, permanganic anhydride is one of those compounds you make in situ right when you need it as it doesn't like to hang around all too long.

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If its permanganic anhydride, will it form an acid wen added to water?

ahhh sorry

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out of curiosity, does anybody know if permanganic acid is reasonably stable?

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Honestly, I wouldn't think so. This is mostly from experience with potassium permanganate solutions which are at a low pH. In those instances, the MnO4- ion gets reduced under acidic conditions to form Mn(2+) and some water. So I would think that permanganic acid wouldn't be all too stable.

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wat would HMnO4 decompose into when in solution?

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I'm more interested in the reaction between the ethanol and permanganic anhydride.

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Mn2O7 is highly unstable. It is definitely dangerous to produce this anhydride; it decomposes explosively.

Often, a tiny amount is produced by putting a single crystal of KMnO4 in conc H2SO4.

But no more!

There was an accident many years ago in a lab here, where someone made a dangerous mistake. They were going to produce chlorine by mixing solid KMnO4 with aqueous HCl. But someone made a fatal mistake and mixed solid KMnO4 with conc H2SO4. Immediately, a significant amount of Mn2O7 was formed, and exploded violently, completely destroying the fume hood!

Avoid this dangerous chemical!

As a contrast, the analogous Tc and Re oxides are stable solids.

The corresponding anions are not strongly oxidizing anions in contrast to the permanganate ion.

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how does sulfuric acid cause the parmangnic anhydryde to form?

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sulfuric acid, when mixed with any inorganic salt, will form the mineral acid of the salt and the bisulfate or sulfate, depending on the proportions. ex:

MCl+H2SO4-->HCl+MHSO4

2MCl+H2SO4-->2HCl+M2SO4 (with less of a yield)

and so,

KMnO4+H2SO4-->KHSO4+HMnO4

but sulfuric acid is quite a strong dehydrating agent, and if concentrated enough, it dehydrates the permanganic acid to form the anhydride of permanganic acid.

permanganic acid is explosively unstable, yes, but it's not like TCAP. dont put it near a reducing agent and you'll be ok. the problem is that it readily decomposes slowly, yielding ozone.

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dont put it near a reducing agent and you'll be ok.

Well - actually, no.

Mn2O7 in itself is highly unstable, an may detonate violently upon heating or even a slight mechanical shock! Even without reducing agents present.

Comparably unstable compounds are chlorine(VII) oxide, Cl2O7, and anhydrous perchloric acid (~100% HClO4).

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chlorine (VII) oxide, Cl2O7 and anhydrous perchloric acid are exactly the same.

and yeah, heat it or hit it with a hammer and it will decompose. but im talking about storage. if it's stored properly, it shouldnt be problematic.

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Sulfuric Acid is also a pretty potent oxidizing agent. It's not up there with nitric acid, but it is still pretty potent. If the ambient temperatures are increased, then the oxidizing ability increases as well. This is why if you put a piece of copper metal into room temperature sulfuric acid you won't see much, if any, reaction. But if you bring that sulfuric acid up to a high temperature, it will start oxidizing the copper and you'll see a pretty good reaction.

H2SO4 (concentrated) is also able to oxidize some halides to their halogens. If you mix NaF and sulfuric acid, you'll get HF and some bi/sulfates of sodium. If you mix NaCl and sulfuric acid, you'll get HCl and some bi/sulfates of sodium. If you mix NaBr with sulfuric acid, you'll get some HBr but you'll also get some elemental bromine along with your sodium (bi)sulfates. This is because the sulfuric acid is able to partially oxidize the bromide ion into elemental bromine, but not at a full rate. As a result you get a nasty mixture of sulfur oxides, HBr and Br2. Definitely NOT something you want to be around. Now if you mix NaI and sulfuric acid, you'll get iodine and sodium (bi)sulfate and almost no HI. The iodide ion is very easily oxidized into elemental iodine and almost not hydrogen iodide is formed. (That's why the commerical production of HI uses concentrated phosphoric acid since H3PO4 is a very poor oxidizer).

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sulfuric acid seems to only be a good oxidizer at high concentrations and high temperatures.

also, theoretically, you may be right about the iodide salts, but experimentally i've found that significant amounts of HI are evolved, with a reasonable amount of I3- in solution. i also found that while SO2 was evolved, a significant amount of the acid reduced all the way to H2S.

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Sorrt, my mistake!

I mean "chlorine(VII) oxide, Cl2O7, and water free perchloric acid (~100% HClO4)."

These are not the same.

Storage of Mn2O7?

Hmm, it would be dangerous to store that stuff. I wouldn´t try.

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Commercially available perchloric acid is maximum 73% HClO4.

Higher concentration than 85% HClO4 is denoted "anhydrous perchloric acid".

"Handling Anhydrous Perchloric Acid (Greater than 85%)":

Chlorine(VII) oxide, Cl2O7, sometimes denoted "perchloric anhydride", is not the same thing as "anhydrous perchloric acid".

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"Sorrt, my mistake!

I mean "chlorine(VII) oxide, Cl2O7, and water free perchloric acid (~100% HClO4)."

These are not the same."

yes they are. think of it. chlorine (VII) oxide. how can you do that? it's not ClO4 or ClO3. nope. must be Cl2O7. 7*2=14. 2*7=14. then there's Cl2O7. anhydrous perchloric acid. well, that's basically HClO4-H2O. only 1 hydrogen, so you have to say 2HClO4-H2O-->Cl2O7. Cl2O7+H2O-->2HClO4. Cl2O7 is perchloric anhydride

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