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Topic: KMnO4 as an oxidizing agent: Avoiding MnO2 ppt formation  (Read 4769 times)

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Offline curiouscat

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KMnO4 as an oxidizing agent: Avoiding MnO2 ppt formation
« on: October 09, 2013, 01:18:27 PM »
Is there a way to avoid getting an MnO2 ppt when using KMnO4 as an oxidizing agent? Preferably some strategy that does not  involve a highly acidic pH.

I had read somewhere that at pH above 12 the mangnate ion would get preferentially formed and I was hoping this might prevent the MnO2 ppt but I couldn't get this to happen.

Any other ways to prevent or solubalize MnO2 solids in situ?

Offline Hunter2

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Re: KMnO4 as an oxidizing agent: Avoiding MnO2 ppt formation
« Reply #1 on: October 10, 2013, 12:59:00 AM »
At pH higher then 4 MnO2 will be formed in any case, this cannot be prevented. In lower pH Manganese-II is built up and MnO2 get dissolved. Right at very high pH Manganate MnO42- is also formed, but still some manganese dioxide.
Some MnO2 is created from the manganate with an reaction on the glass wall of the flask or beaker at high pH. Probably some catalytic effect.

2 MnO42- + 2 H2O => 2 MnO2 + 4 OH- + O2

Offline curiouscat

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Re: KMnO4 as an oxidizing agent: Avoiding MnO2 ppt formation
« Reply #2 on: October 10, 2013, 01:21:52 AM »
At pH higher then 4 MnO2 will be formed in any case, this cannot be prevented. In lower pH Manganese-II is built up and MnO2 get dissolved. Right at very high pH Manganate MnO42- is also formed, but still some manganese dioxide.
Some MnO2 is created from the manganate with an reaction on the glass wall of the flask or beaker at high pH. Probably some catalytic effect.

2 MnO42- + 2 H2O => 2 MnO2 + 4 OH- + O2

So in theory, asides of the catalytic glass wall side reactions, it is indeed possible to get the soluble manganate ion entirely without any MnO2?

Offline Hunter2

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Re: KMnO4 as an oxidizing agent: Avoiding MnO2 ppt formation
« Reply #3 on: October 10, 2013, 03:53:44 AM »
Yes you can obtain the manganate ion, but if this is free of manganese dioxide I don't know. We use an application in an alkaline Permanganate etch bath for cleaning the holes of printed circuit boards. The used solution will be recycled by electrolysis. 

MnO42- => MnO4- + e-

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