Bedlasky
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Manganese heptoxide in very low concentration
Hi.
I know that manganese heptoxide is very unstable and dangerous compound. But I've got idea make really dilute solution of manganese heptoxide just for
demonstration of manganese colours (manganese heptoxide forms in conc. sulfuric acid MnO3+ ions which are dark green). If I'll added 1-2 drops of
0,015M solution of KMnO4 in to conc. H2SO4 it will form only very small amount of Mn2O7. After doing few photos I'll pour in to large amount of cold
water and add small amount of sodium metabisulfite. Is this experiment safe?
[Edited on 30-6-2019 by Bedlasky]
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fusso
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Not very, as there's too much water in 0.015M KMnO4. Don't add water to conc H2SO4! I think adding a small KMnO4 crystal to a lot of cH2SO4 is safer.
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Sulaiman
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The risks associated with adding water to concentrated sulphuric acid in a small scale environment are massively exagerated.
If mixing litres or tons then different rules apply,
but at small scale it is exceedingly difficult to get boiling.
e.g.https://www.youtube.com/watch?v=RS_TrEbaizg
Although a few crystals of permangante could be added to water to see the purple colour,
and a few crystals in sulphuric to see green,
instantly converting a purple liquid to green would be more memorable, I think.
The problem is that most literature is over cautious (scared of litigation),
so IF something did go wrong your actions could be considered irresponsible - in this litigious world.
As you are demonstrating oxidation levels I assume that this will be for a class of students with a basic appreciation of chemistry,
so adding a very small additional risk should be part of their education.
How much can be learned from completely risk-free chemistry ?
(A lot, but not enough)
I suggest that you try the experiment by yourself a few times to feel confident.
(Being an SM member) I'd be inclined to also make a LITTLE manganese heptoxide to show how highly oxidising it is.
e.g. https://www.youtube.com/watch?v=BowId4YyRgQ&t=2s
How many of your students get stimulated/excited by a colour change ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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Pumukli
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"How many of your students get stimulated/excited by a colour change ?"
Well, if it is on a pregnancy test strip... 
More on-topic: I still remember when I prepared some Mn2O7 and ignited the vapours of ethanol with it! It is definitely a "magic" thing to remember.
And to be honest, I didn't see it as something very dangerous.
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Bedlasky
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Sulaiman: I don't have any students  . I'll have it for my website - I want to
show few unusuall compounds of manganese and this is one of them.
Thanks for videos. I find some instructions for experiments with Mn2O7 on Woelen's site too. Maybe I'll try put on small amount of Mn2O7 drop of
ethanol. I normally do not do explosive experiments, but this could be interesting.
Pumukli:
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Tsjerk
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I found this strange difference between the SM wiki and Wikipedia.com...
wikipedia.com says the heptoxide is soluble in carbon tetrachloride.
SM wiki
says "immiscible with carbon tet"
text
I don't know how soluble potassium permanganate is in carbon tetrachloride, but I could imaging making some manganese heptoxide and then dissolving
that in carbon tetrachloride could give a solution in CCl4, as sulfuric acid is not miscible with CCl4.
Edit: I think something changed between posting GUI now and posting GUI here:
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...
The GUI seems to have changed in the mean time. If I edit a post posted back then, I get the options to do the formatting as above. Not anymore
though. Just so you know.
See the link I posted in the pid616431 post, it goes to google.com, like in the third link in this post. Here the formatting doesn''t work. In the
edit I did in the pid616431 post it does work.
[Edited on 30-6-2019 by Tsjerk]
[Edited on 30-6-2019 by Tsjerk]
[Edited on 30-6-2019 by Tsjerk]
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Pumukli
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" Maybe I'll try put on small amount of Mn2O7 drop of ethanol."
To clarify things: I DID NOT let the ethanol droplet(s) fall onto the heptoxide! That kind of "magic" probably would had been too much for my liking!
I soaked a small wad of cotton in my father's after shave spirit, secured the cotton wad at the end of a 25cm long iron wire and held the wad ABOVE
the heptoxide a few centimeters! No direct contact between the heptoxide and the alcohol soaked cotton!!! The descending heavy alcohol vapour was
ignited! This is the "magic": you get something burning without obvious contact!!!
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Herr Haber
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Quote: Originally posted by Sulaiman
||
|| The risks associated with adding water to concentrated sulphuric acid in a small scale environment are massively exagerated.
|| If mixing litres or tons then different rules apply,
|| but at small scale it is exceedingly difficult to get boiling.
|| e.g.https://www.youtube.com/watch?v=RS_TrEbaizg
20 % H2SO4 + 80 % water will reach boiling temperature
Nothing to do with the current topic but when adding 20% Oleum to 96% H2SO4 you instantly understand why when making the acid they add SO3 to H2SO4
(then dilute it down) instead of adding SO3 to water.
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Bedlasky
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Pumukli: That's a very interesting experiment!
I read about the reaction of Mn2O7 with droplet of ethanol here:
http://woelen.homescience.net/science/chem/exps/mn2o7/index....
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