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Author: Subject: Manganese Heptoxide type reaction.
tom haggen
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[*] posted on 12-12-2004 at 20:53
Manganese Heptoxide type reaction.


My teacher did this cheesy little experiment with ethanol, sulfuric acid, and potassium permanganate. She added the ethanol to the sulfuric acid which floated on top of the acid if I remember correctly. Then she added small amounts of potassium permanganate. Once it sank threw the ethanol, and contacted the sulfuric acid it reacted with the acid forming manganese heptoxide, which in turn reacted with the ethanol in the form of combustion. It made like sparkly lights for like an hour:D. Anyway I have a few questions that I never seemed to have asked her because she was a dumb "B".

1.) When you first add the ethanol to the H2SO4 does it form some diethyl ether?

2.) Would any organic solvent work for this trick so long as it doesn't react too severely with H2SO4?

3) What is the formula for manganese heptoxide, and how would you right a balanced net equation for the reaction between KMnO4 and H2SO4?

[Edited on 13-12-2004 by tom haggen]




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[*] posted on 12-12-2004 at 20:56


3) 2KMnO4 + H2SO4 --> Mn2O7 + K2SO4 + H2O



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BromicAcid
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[*] posted on 12-12-2004 at 21:01


1.) Concentrated sulfuric acid mixed with ethanol will likely form some diethyl ether, but not enough to be noticeable.

2.) Ethanol doesn't sound safe for this reaction to me so I have no clue what criteria would be necessary to determine if it was safe considering it doesn't sound safe to begin with. For example, manganese heptoxide can detonate very spontaneously with many organics, I would not risk trying to change something in a reaction that might risk detonation with the swapping of a reagent.




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[*] posted on 12-12-2004 at 21:06


I think this is a wellknown chemistry demo experiment, which has the purpose of showing sparks in liquid. If it was that unsafe I guess they wouldn't be doing it as a demo experiment ... teachers these days being overly concerned with H&S, but completely forgetting that the pupils get bored with chemistry quickly :(
I can find the official protocol over christmas if desired.




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[*] posted on 13-12-2004 at 12:19


A very important thing in this demonstration is that the H2SO4 is NOT mixed with the ethanol. The Ethanol must float on top of the H2SO4, the less they mix, the better the experiment works.
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tom haggen
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[*] posted on 13-12-2004 at 13:06


Even if the ethanol mixes with the sulfuric acid, wont they separate if you let them sit for a while. Bromic, the reason this isn't that dangerous is because the manganese heptoxide forms in small amounts and reacts with the ethanol the instant if forms. It gives an effect of all these mini type explosions underwater.

[Edited on 13-12-2004 by tom haggen]




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neutrino
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[*] posted on 13-12-2004 at 14:14


I’d imagine that you’d be left with a layer of ether and one of acid with some water in it. You might get a little ethanol back, but this is doubtful. I don’t see why the reaction wouldn’t work with ether, though.
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tom haggen
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[*] posted on 16-12-2004 at 12:22


Just how dangerous is Mn2O7? If I wanted to make like 5 grams of this stuff just for experimentation, would I be putting myself in danger. Can Mn2O7 be stored in any other containers besides those made of glass? I.E. would you be able to put this chemical in HDPE or would it oxidize the polymer?



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[*] posted on 16-12-2004 at 14:20


All I’ve ever heard of anyone making is very small amounts. You should be able to store it in anything noncombustible. Metals would probably corrode and plastics (except maybe PTFE) would be destroyed. By the way, manganese heptoxide tends to decompose by itself at room temperature. Just thought you should know.
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[*] posted on 16-12-2004 at 15:21


You'd need to store it below -10C. Otherwise it will slowly decompose yielding ozone and oxygen. This can be troublesome in closed vessels as high ozone concentrations are prone to detonation.



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tom haggen
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[*] posted on 16-12-2004 at 15:57


-10C is pretty cold. Colder than I have capabilties of maintaining. I guess I will just have to make it as I need it. I still am in the dark on whether or not it will react with HDPE though. I was just thinking of filling small test tubes with Mn2O7 and placing them in a hydrocarbon, and tossing them for little fire ball type explosions. The only problem is most of the test tubes I have only have lids made out of HDPE. I guess it wont matter if I use it when I make it;)

[Edited on 17-12-2004 by tom haggen]




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[*] posted on 16-12-2004 at 16:04


I believe Axt has a video on his site of manganese heptoxide reacting with xylene, I'd hardly call it a "small fireball type explosion". Personally I won't even make the stuff, I've heard sunlight can cause it to detonate as can shock. Plus, as Vulture said, it decomposes at ambient temperature forming ozone, not good...



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[*] posted on 16-12-2004 at 17:05


Tom: if you have a blowtorch, you can try ampouling it, although it does require a certain degree of skill.
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[*] posted on 16-12-2004 at 18:28


I'm thinking i'm going to make about 5 grams and use a pipet to drip small amounts on to a puddle of organic solvent. To get a feel for the chemical. I'm definitely going to use it as I make it though just because I'm paranoid about storing stuff that is dangerous.

I've got a blow torch lying around but I have no idea what ampouling is.

I've also seen axt's video, but I was thinking much smaller amounts, like I said I have to get a hands on feel for how this stuff reacts.

[Edited on 17-12-2004 by tom haggen]




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[*] posted on 16-12-2004 at 18:46


Ampouling is sealing something in an ampoule. First, you take a glass tube and seal one end shut be pulling on the end. You can then heat this to get a rounded end (like a test tube). Next, you draw the other end out to a thin tube through which something can be added. Add the material and quickly seal the tube. It’s simple once you get some experience.
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tom haggen
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[*] posted on 16-12-2004 at 20:58


So thats how they seal all those gases like fluorine, NO2, etc. in those glass bulbs in my text book:D



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[*] posted on 16-12-2004 at 21:03


Before you go playing with your blowtorch, you do realise that Mn2O7 will detonate when heated, dont you.

I have a test tube full of the stuff, from a failed naphthalene diozonide attempt. Sits up the back in a large 1/4" steel vessel, too scared to go near it :)

[Edited on 17-12-2004 by Axt]
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[*] posted on 17-12-2004 at 01:09


I still have my hands now, and if I were going to lose them they would be gone by now.;)



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[*] posted on 17-12-2004 at 03:27


That's the point of having a narrow neck the pipette can fit through: it doesn't get any liquid on it and can be sealed quickly. If you're worried about this, you might want to leave a lot of extra space in the ampoule.
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[*] posted on 17-12-2004 at 04:26


What if later, when you wanna open the ampoule to get the stuff out, and when you crack it, the shock causes it to detonate? You'll be impaled with glass shards :(



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[*] posted on 17-12-2004 at 04:49


Thats only if you can blowtorch the tube shut without the heat setting it off. :P

Mn2O7 doenst evaporate easily does it?

Whats wrong with storing it in a glass-stoppered glass bottle, and if it doesnt react with PTFE, use teflon thread sealing tape (from a hardware store) to make an airtight seal around the stopper?

Then again, why store it at all?
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[*] posted on 17-12-2004 at 05:09


It does.

"The oil is green by reflected light and reddish-purple by transmitted light. It's fairly volatile, also, and hydrates to a purple fog if you're brave enough (or stupid enough) to breathe over a container of the stuff. "




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[*] posted on 17-12-2004 at 05:17


Damn, why are all the cool compounds volatile :(, jk!

Well, someone mentioned before that it probably doesnt react with PTFE, so a glass bottle + glass stopper with PTFE tape to form an airtight plug, is a good option for storage (although storage isn't a good option).
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[*] posted on 17-12-2004 at 06:15


A couple of months ago I made a small ammount of manganese heptoxide in a 50mL beaker. I got the pure green Mn2O7 liquid(very little of it) floating on top of the sulfuric acid and a very dark green solution of Mn2O7 in sulfuric acid.

The day it was prepared: When the pure liquid was dripped onto a kleenex instant flash and the kleenex caught fire. The solution of Mn2O7 in sulfuric took abot 10s to catch the kleenex on fire.

The next day: Pure liquid took 5-10s to catch the kleenex on fire. Less "fwump" upon ignition than the previous day. The solution of Mn2O7 took almost a min to catch the kleenex VERY weak "fwump"

2 weeks later: The pure liquid has dissapeared. The contents of the beaker were brown and gooey. Nothing in the beaker was able to catch kleenex on fire.



[Edited on 17-12-2004 by rogue chemist]




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[*] posted on 17-12-2004 at 10:24


The tape used for plumbing is not always impervious to vapors. IME, the stuff is either impure or permeable to gases and vapors. If you want to make some chemically resistant vials, get some decent sheet. As always,I recommend trying ebay.
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