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Author Topic: Weird reaction, how it works? (Potassium Permanganate and Sulfuric Acid)  (Read 12438 times)

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_eMiliO_

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Good Evening people,

First of all, this is my first post here and I have to say that this forum is great! I think I'll get a lot of good information here. And one more thing before the beginning, sorry for my English, I'm Brazilian and I don't have such a good language experience!

Well, Today on my chemistry class we went to the laboratory and tried some different reactions to try to calculate their enthalpy values and prove it. Everything went OK, and we had made all the programmed things so we decided to make different reactions and asked to the teacher what to do. She talked to us about an interesting reaction between Potassium Permanganate and Sulfuric Acid, explained to us how to make it and we did. It was like this:

Put 1g of Potassium Permanganate on a bottle (I don't know how this is called in English "cadinho")
and 5ml of sulfuric acid 1mol/L

It doesn't show the reaction, but we know it's happening. So, we put a cotton (Algodão in Portuguese, if that's not how you call it) which had been immersed in ethyl alcohol.

And it started to burn, without any fire or high temperatures. That obviously started a discussion about how did it happen and the teacher didn't tell us how it happened, just told us to search in books and internet but we can't find anything else the simplest reaction between the first two reagents but it doesn't show anything to us, we want to know why that happen, it's obvious that the ozone helps the combustion of the alcohol, but we think that there is something which starts the reactions without heat, something like an instable molecule which interacts with the oxidizable organic compound!


The reaction we found in wikipedia:
6 KMnO4(aq) + 9 H2SO4(aq) → 6 MnSO4(aq) + 3 K2SO4(aq) + 9 H2O(l) + 5 O3(g)

I searched here on the forum, but I didn't find anything like these reactions, just talking about the first reaction!

Thanks a lot guys!
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DevaDevil

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ozone has such a high oxidizing power, the reaction to oxidize (burn) ethanol happens at room temperature. No need for more driving force by elevating temperatures.

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_eMiliO_

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Well, After discussing some time my teacher asked us why it happened, I obviously tried that answer but she didn't accept, she said that there was one more thing which would burn it!

I don't know who is right, you or my teacher, so let's wait someone more to reply.

Thanks!
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tflint89

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This is a long shot but what if the ozone oxidises some of the Mn2+ ions in solution (assuming MnSO4 is soluble) and is reduced to oxygen gas in the process?

This oxygen should burn the volatile organic compound, assuming again that the ozone oxidation is exothermic enough to provide enough heat to surpass the large activation energy for this reaction...




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DevaDevil

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in concentrated Sulfuric acid (1 M does not count as concentrated) permanganate is reacted to manganese (VII) oxide, which in turn is reduced to manganese (IV) oxide, giving off heat and molecular oxygen.
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