flakestoday
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Questions about H2O2 and KMnO4 in aqueous H2SO4
Hello all, so I am putting together a redox demonstration for a class, and I had a couple questions about the reaction of KMnO4 with
H2O2.
So I know that when this reaction is done in a solution of H2SO4, it will yield a clear solution, according to the equation:
2KMnO4 + 3H2SO4 + 3H2O2 ---> K2SO4 + 2MnSO4 +
6H2O + 4O2
(I am aware there are multiple ways to write this equation but I am just sticking with this for now) My question is, will H2SO4
and H2O2 in the same solution give any Caro's acid? I am going to have to dispose of all the materials after the demonstration
and I just want to know what I am dealing with when I do this reaction. I plan on keeping everything pretty dilute, but presence of
H2SO5 is something I definitely want to be aware of. I was also thinking of using phenolphthalein as an indicator for
neutralizing the solution afterwards, and I believe that presence of Caro's acid would kind of make this a no-go. Aside from the safety issue, could
formation of Caro's acid mess with the stoichiometry stated above? The permanganate is being reduced here, and if Caro's acid is a strong oxidant,
wouldn't that effectively be just sequestering H2O2?
I could do this in excess of H2O2, but again if there is any Caro's acid formation, excess H2O2 could be
an explosion hazard, right?
Now I suppose this could be avoided by making a solution with permanganate and sulfuric acid, and then adding the peroxide to that solution, but I had
planned on pouring the permanganate solution into a solution containing the peroxide and sulfuric acid - kind of stupid but I think it would look
significantly more interesting to the people for whom I am doing this demonstration. Obviously if safety is an issue (or if the stoichiometry could be
thrown off) I will not do that, but I just thought it would be worth it to ask, after not finding much online or on here about the specifics of this.
(I did do a search before posting this, but it is possible that something slipped past, so my apologies if that is the case.)
Thanks!
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unionised
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No.
Or, at least so little that it would be rather hard to detect.
Caro's acid is unstable in the presence of water.
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Bedlasky
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H2SO5 is prepared by mixing concentrated H2SO4 and 35% H2O2. In this mixture is small amount of water. But in your mixture is huge amount of water, so
almost all H2SO5 is hydrolyzed. Don't worry about explosions etc. This reaction is used for manganometric determinations of peroxides. I did it
thousand times and I had not any accidents. It's very simple and safe demonstration.
Another cool demonstration is pouring some 30% H2O2 on solid KMnO4 in conical or flatbottom flask. There is formation of huge amount of water vapor.
Reaction is exothermic, so be carefull. Don't add too much H2O2.
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flakestoday
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Thank you all for the info! The demonstration was a big success.
Also just now noticing I made a mistake in my chemical equation -- it should have eight oxygen on the products side, my bad.
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