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Topic: Mn+2 oxidation with PbO2  (Read 226 times)

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Offline paulE

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Mn+2 oxidation with PbO2
« on: November 09, 2021, 04:19:11 PM »
Hi
I produced some PbO2 by dissolving a lead pipe piece in HNO3,then precipitate with NaOH and oxidation with domestic bleach.
The filtered brown power does not disolve in HNO3 and releases Cl2 from HCl, so i think is truly PbO2

Books say to recognize Mn+2, you add the Mn sample to a tube with concentrated (I used 65%) HNO3, some PbO2, heat a little and if Mn+2  is there, a purple color will develop due to MnO4...
No way...I tryed several times and all I get is a brown precipitate of PbO2 in the bottom of the test tube and no colour...I'm sure there is Mn there because i put some MnSO4 there just to test if this technique is true. And nothing happens! What is happening here?

I want this to analyze some stones with black spots, to check if they are Fe or Mn. I mixed some pieces witk KNO3 and NaOH,melt all together, and a sligh green colour developed, but i'm not sure if it is Mn there..
« Last Edit: November 09, 2021, 04:37:08 PM by paulE »

Offline paulE

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Re: Mn+2 oxidation with PbO2
« Reply #1 on: November 21, 2021, 03:01:30 PM »
I will answer myself, but not with the expected results.

If I add some ml of domestic bleach to the solution, and heat it a little, a violet MnO4 color inmediatly appears. No need to add PbO2. I thought this could be due to the NaClO of the bleach becoming clorate as soon is heated,then oxidizing the Mn. But if I leave the bleach, and the Mn+2 solution some hours without heating, same color appears. Is ClO- ion oxidizer enough to promote Mn+2 to MnO4 or is the chlorate?

I read something about this reaction with PbO2 having chlorides as inhibitor, but no Cl ions are in my solution.Anyway, ...big deception with PbO2, as I read the reaction is very good to discover manganese ions, and i have no single trace of this reaction to be working.

Offline Borek

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Re: Mn+2 oxidation with PbO2
« Reply #2 on: November 21, 2021, 03:48:18 PM »
Is ClO- ion oxidizer enough to promote Mn+2 to MnO4 or is the chlorate?

Judging from the standard reaction potentials ClO- should be enough to oxidize Mn2+ to MnO4-. Doesn't mean the reaction will proceed as expected, plenty of fine prints, as is often the case in chemistry.
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