woelen
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Mixture of potassium monoperoxysulfate and potassium peroxodisulfate
Last weekend, when I was in a hardware store, buying some gardening tools, I ran towards a big bottle with 1 kg of swimming pool oxygenation agent
(brand: Interline) and the label tells it has two ingredients, but it does not tell in which ratio:
1) K2SO4.KHSO4.2KHSO5 (oxone)
2) K2S2O8 (potassium peroxodisulfate)
The material is a free flowing perfectly dry fine granular solid, white like snow.
I already have pure K2S2O8 but never found a source for peroxymonosulfate, so I decided to grab the bottle and do some experiments with it.
My observations so far: K2S2O8 is only sparingly soluble in water (like KClO3, it dissolves with difficulty). The newly purchased mix is soluble very
easily. If a large spatula of this is added to water, then just a few swirls and all of it is dissolved, giving a clear colorless solution. I expected
it to dissolve much more slowly, because of the K2S2O8 in it.
K2S2O8 (in fact all peroxodisulfates) reacts with silver nitrate, dissolved in nitric acid to give a brown solution of silver(III) (I wrote about that
in other threads). The newly purchased material does not. It actually does the opposite, when added to such a brown solution, it makes the solution
colorless again and small amounts of gas are produced in that reaction (I assume O2).
K2S2O8 and the newly purchased chemical do not react with dichromate to give a deep blue peroxo complex. On addition of H2O2 the deep blue complex is
formed. This complex apparently does not react with monoperoxysulfate, nor with peroxodisulfate.
When pure K2S2O8 is mixed with the newly purchased chemical and water is added, then the K2S2O8 does not dissolve easily, while the other material
quickly dissolves.
I now start to doubt the presence of K2S2O8 in my new chemical (that would be nice!). Is there any way to assess the presence of K2S2O8 in a mix with
oxone? I hope the material is pure oxone and the label is wrong.
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ScienceSquirrel
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Is this them?
http://www.interline-products.com/8726.htm
I have dealt with APC Pure before and found them very good and they sell Oxone.
http://www.ebay.co.uk/itm/500gm-Potassium-Persulphate-99-PCB...
[Edited on 16-7-2013 by ScienceSquirrel]
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woelen
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This is not oxone, but the peroxodisulfate.
It is quite confusing, but there are two main classes of peroxosulfates. One class is derived from H2S2O8, HO-S(=O)2-O-O-S(=O)2-OH, peroxodisulphuric
acid, and the other class is derived from H2SO5, HO-S(=O)2-O-O-H, peroxymonosulphuric acid.
These two peroxo compounds seem to have quite different properties. The peroxodisulfate is the stronger oxidizer (redox potential of appr. 2 volts),
but it also is a very sluggish oxidizer. I want to find out whether I really have a mix of these two, or only the peroxymonosulfate (together with
inert sulfate and bisulfate).
If there is a qualitative chemical test, specific for peroxodisulfate which works in the presence of peroxymonosulfate, then I would like to know of
such a test.
[Edited on 16-7-13 by woelen]
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ScienceSquirrel
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My mistake, I see that it is not Oxone.
This is the Technical Data Sheet for Oxone;
http://www.runyoutech.com/pdf/potassium-monopersulfate-speci...
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AndersHoveland
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From what I understand (might be wrong here), both peroxydisulfate and peroxymonosulfate decompose into sulfate radicals in boiling solution.
•OSO3‒
Reduction Potentials:
Persulfate (acidified) 2.01v
Persulfate (heated) 2.6v
Iron ions can also catalyze the oxidizing power of persulfate at ambient temperatures; I suspect this takes place through the transient formation of
FeO42-. There are other similar reactions in organic chemistry where rhenium or osmium oxides are used as the catalyst to
increase the oxidizing power of hypochlorite.
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The_Davster
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Titration would work, but you would need a digital pH meter.
If I remember correctly, the pH at half of the equivalence pH point during a titration is the pKa of each proton. So you could titrate pure oxone,
pure peroxydisulfate, and the mix and see if you see just two inflection points, or four when pH vs volume of titrant added is plotted.
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