Sciencemadness Discussion Board - Potassium Permanganate Decomposition Products

Potassium Permanganate Decomposition Products

Thomas Winwood - 24-12-2004 at 18:14

I intend to break down my potassium permanganate by heating to about 500 K. I wonder how will I seperate the resulting manganese dioxide (useful) from potassium manganate (not-so-useful unless I can get manganese dioxide out of it).

If potassium manganate is soluble (as suggested by an exam paper I found on Google) then I can seperate it from insoluble manganese dioxide by dissolving it and filtering out the MnO2.

Am I right? How else would I seperate out the K2MnO4? (Google has barely anything, nor my data book, nor sci.chem archives.) And can I get more MnO2 from the potassium manganate? If so, how?

budullewraagh - 24-12-2004 at 19:17

you cant dissolve it in water, as adding water to potassium manganate oxidizes it to permanganate. you may want to try a saturated KOH solution though, as that would prevent the oxidation

HNO3 - 24-12-2004 at 21:29

500 K???

Other than that, I believe you can form MnO2 by mixing and organic solvent and a KMnO4 solubion and filter off the precipitate formed after a day or so. Never tried it myself, as I get my MnO2 from cheap nonalkaline batteries e g Lantern batteries.

budullewraagh - 24-12-2004 at 21:48

careful what solvent you use:\

Marvin - 25-12-2004 at 02:14

Add manganese sulphate (garden center, pharmacy) to potassium permanganate. Keep the permanganate in excess and filter off the MnO2.

What is it you need MnO2 for that permanganate cannot be used?

cyclonite4 - 25-12-2004 at 04:41

Even thought they have similar application, maybe he wants it for it's insolubility in water?

budullewraagh - 25-12-2004 at 05:32

MnO2 can be found at pottery suppliers. i think he wants the manganate

Thomas Winwood - 25-12-2004 at 08:49

Quote:

Originally posted by budullewraagh
MnO2 can be found at pottery suppliers. Maybe true, but as was discussed in another thread it's usually better practice to make your own. i think he wants the manganate Only to make yet more MnO2. I prefer to go by the book in preparations, and my book tells me to use MnO2.

[Edited on 25-12-2004 by Thomas Winwood]

HNO3 - 25-12-2004 at 09:08

"Use MnO2" for what?

budullewraagh - 25-12-2004 at 09:13

the thing that puzzles me is the fact that potassium permanganate decomposes at 210 celsius, whereas potassium manganate decomposes at 195 celsius

cyclonite4 - 25-12-2004 at 19:35

So basically decomposing the permanganate would cause a double decomposition to MnO2 because the pemanganate decomp. temp. is higher, interesting.

Protium - 25-12-2004 at 20:57

If it is MnO2 that you desire, It can easily be made from KMnO4 and an alcohol.

Make a solution of KMnO4 in H2O, and slowly add an alcohol.

It may help to add a little H2SO4 but this will promote further reduction of the Manganese to the +2 state. Manganese in MnO2 is in the +4 state which is what we want.

Methanol (HEET Brand) or denatured alcohol will work. The corresponding aldehyde will be formed from the oxidation of the acohol.
methanol + [O] --> formaledhyde
ethanol + [O] --> acetaldehyde
These aldehydes will escape as gases due to their low bp's, though a small amount may be futher oxidized to formic or acetic acid. No Problem as they can be removed by evaporation/distilliation.

Anyway, the MnO4- will be reduced to MnO2.

Mixing the bulk of MnO2 formed in H2O, then filtering will remove most of the unreacted KMnO4 salts as well as any Mn in the +2 state.

I do not really think that MnO2 is oxidized back to MnO4 by H2O, so mixing in H2O and filtering should be perfect to retrieve relatively pure MnO2.