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Topic: What happens when solutions of KMnO4 and Na2S2O3 are mixed?  (Read 34786 times)

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Offline sweet_ana

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What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« on: January 09, 2007, 03:00:53 PM »
I have found somewhere a problem who sounds like this: "What volume of Na2S2O3 0.050 N is necessary to react completely with 0.0032 g KMnO4?" But I haven't found anywhere the reaction betwen them and experimentally I didn,t notice anything. Does anyone have any idea about it?

Offline FeLiXe

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #1 on: January 10, 2007, 11:34:16 AM »
the thiosulfate gets oxidised probably to sulfate (or just sulfite?)

permanganate gets reduced to MnO2 or Mn2+

this is a fairly complicated system and I don't think it's easy to tell the products. you would probably need to know the pH too
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Offline Albert

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #2 on: January 10, 2007, 05:12:16 PM »
KMnO4 + Na2S2O3 + H2O = K2SO4 + Na2SO4 + MnO2 + KOH

It has to be balanced, of course.

Offline Borek

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #3 on: January 10, 2007, 06:07:42 PM »
Don't forget

S2O32- -> S4O62-

which is used for I2 determination. As FeLiXe stated - a lot depends on the redox potential (strongly pH dependent for permanganate) and reaction mechanism.
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Offline Albert

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #4 on: January 10, 2007, 07:14:50 PM »
Don't forget

S2O32- -> S4O62-

which is used for I2 determination. As FeLiXe stated - a lot depends on the redox potential (strongly pH dependent for permanganate) and reaction mechanism.

Could be, of course.

Mind you, looking at sweet_ana's question, aren't you tempted to answer 2 KMnO4 + Na2S2O3-> 2 NaMnO4 + K2S2O3 too?

Offline Borek

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #5 on: January 11, 2007, 04:01:35 AM »
Mind you, looking at sweet_ana's question, aren't you tempted to answer 2 KMnO4 + Na2S2O3-> 2 NaMnO4 + K2S2O3 too?

That's ridiculous :) I am sure the question is about redox reaction.
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Offline sweet_ana

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #6 on: January 11, 2007, 09:10:36 AM »
KMnO4 + Na2S2O3 + H2O = K2SO4 + Na2SO4 + MnO2 + KOH

It has to be balanced, of course.

I think theoretically it is possible, but I tried it experimantally (just mixing the solutions, without heating, but KMnO4 doesn't need temperature to reduce to MnO2) and no precipitate appeared.

Offline Kunisch

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #7 on: January 11, 2007, 05:23:30 PM »
Hmm..
I havent got all the ins and outs of this but:


8 MnO4 -  + 3 S2O32- + 2 H+  --> 6 SO42- + 8 MnO2 + H2O

Should run okay in Acidic Solution, probably have to warm it a bit, to get the Lillac to blackish color change.

As MnO4- is a strong oxidizing agent i doubt that the reaction:

S2O32- -> S4O62- is going to be stable, it will probably be oxidized SO42-

Also, most redox reactions go a lot smoother with added heat...

Offline Borek

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #8 on: January 11, 2007, 06:43:36 PM »
As MnO4- is a strong oxidizing agent i doubt that the reaction:

S2O32- -> S4O62- is going to be stable, it will probably be oxidized SO42-

Well, original question doesn't contain information about pH, so we don't really know what will be the Mn containing product - it can be Mn2+, MnO2 or even MnO42-. In every case oxidizing strength (redox potential) of MnO4-/something system will be different. That's not to say that S4O62- is THE product, I just don't see any reason to assume it is not :)
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Offline sweet_ana

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #9 on: January 12, 2007, 08:16:38 AM »

Well, original question doesn't contain information about pH, so we don't really know what will be the Mn containing product - it can be Mn2+, MnO2 or even MnO42-. In every case oxidizing strength (redox potential) of MnO4-/something system will be different. That's not to say that S4O62- is THE product, I just don't see any reason to assume it is not :)

I have posted the original problem where I found the reaction, and there is no information about the pH. However, since the solutions are just mixed and no acid or base is present, I think the pH is 7.

Offline AWK

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Re: What happens when solutions of KMnO4 and Na2S2O3 are mixed?
« Reply #10 on: January 12, 2007, 10:27:23 AM »
Permanganate reacts with thiosulfate with acidic or basic solution. Thiosulfate is oxidised to sulfate or tetrathionate (Na2S4O6), respectively.
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