jamit
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Iodate to iodine
I was wondering if potassium iodate could be converted to elemental iodine by adding an acid like HCl and h2o2?. Adding HCl to potassium iodide and
h2o2 produces elemental iodine. Would it work for potassium iodate?
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AndersHoveland
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http://pubs.rsc.org/en/Content/ArticleLanding/2001/CP/b10650...
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madscientist
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Thread Moved
12-11-2011 at 22:57 |
woelen
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@jamit: Hydrogen peroxide does not oxidize iodate to iodine. Try to understand why this reaction does not occur, while the reaction with iodide is
fast and complete in acidic solution. If you understand this, then you have a basic understanding of redox chemistry.
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AndersHoveland
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Someone actually needs to do some experiments ( iodide is a restricted chemical where I reside now due to some ukrainian immigrants proprieting
illicit drug factories )
Iodide is certainly known to rapidly catalyse the decomposition of H2O2. The iodide is first oxidized by the hydrogen peroxide to hypoiodate,
IO[-], which is then reduced by another molecule of hydrogen peroxide back to iodide, with the liberation of oxygen.
H2O2 + I[-] --> IO[-] + H2O
H2O2 + IO[-] --> I[-] + H2O + O2
http://www.demochem.de/chembox_KJ-e.htm
Both hypochlorite OCl[-] and chlorite ClO2[-] are known to be reduced by hydrogen peroxide, so there is no doubt that even if some of the iodide was
oxidized to iodite, the iodite would quickly be converted back to iodide.
Supposedly, hydrogen peroxide oxidizes iodide to iodate.
http://inside.mines.edu/fs_home/dwu/classes/CH353/labs/Clock...
Sodium chlorate, however, does not react with H2O2, unless the solution is acidified. In which case the reaction is:
(2)NaClO3 + H2O2 + H2SO4 --> Na2SO4 + H2O + (2)ClO2 + O2
(moderately concentrated acid is used)
http://www.epa.gov/ogwdw/mdbp/pdf/alter/chapt_4.pdf
So it seems probable that iodate would similarly not react with H2O2, unless of course the solution was acidified. Acidified iodate does indeed react
with hydrogen peroxide, the reaction producing elemental iodine.
"The Reaction between Hydrogen Peroxide and Iodic Acid"
M. G. Peard, C. F. Cullis
http://pubs.rsc.org/en/content/articlelanding/1951/tf/tf9514...
[Edited on 15-11-2011 by AndersHoveland]
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jamit
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@AndersHoveland
Thanks for the information. So acidifying the iodate will allow it to react with hydrogen peroxide. I'll have to try this experiment on a small
scale. Which acid would you recommend?
thanks.
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woelen
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You could try it with sulphuric acid. Hydrochloric acid is less suitable. This acid reacts with iodates, to give chlorine and the deep yellow ICl4(-)
ion.
I also can try this reaction, I never did. But keep in mind that this certainly is a totally different type of reaction than the reaction between
iodide and hydrogen peroxide. In the latter case, the peroxide works as oxidizer. If indeed a reaction occurs with iodate, then it acts as reductor.
You'll see a lot of oxygen forming in that case.
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Panache
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Use oxalic acid,in solution, hot and concentrated to turn your iodate to iodide, cool, then use your peroxide to liberate the iodine from the iodide,
cool filter, wash well with cold water, sublime, dry, then slip and spill it all over the floor whilst moving it to a clear bench to place in a jar,
scrap now contaminated iodine, iodide and iodate from the caustic dirty floor and repeat as before this time not spilling everything at the end.
Voila!
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Panache
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https://www.sciencemadness.org/whisper/viewthread.php?tid=12...
And
https://www.sciencemadness.org/whisper/viewthread.php?tid=11...
Are relevant
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S.C. Wack
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Quote: Originally posted by Panache  | | Use oxalic acid,in solution, hot and concentrated to turn your iodate to iodide, cool, then use your peroxide to liberate the iodine
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Peroxide will not be necessary.
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jamit
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Thanks panachE and wack! I'll try hot con. Oxalic acid on potassium iodate solution tomorrow and post the results.
[Edited on 16-11-2011 by jamit]
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woelen
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I tried mixing a solution of potasium iodate in dilute sulphuric acid with hydrogen peroxide. No reaction occurred. Not even on heating.
I also added oxalic acid to a solution of potassium iodate in dilute sulphuric acid. In the cold these do not react. On heating, there is reaction,
but it is not very fast, and a lot of iodine escapes together with the carbon dioxide, formed in this reaction. It does not work very well.
Out of curiousity I also added hydrogen peroxide to a hot mix of acidified iodate and oxalic acid, in which quite some iodine was formed already. On
addition of the hydrogen peroxide, the liquid lost its brown color, the iodine disappears. A lot of gas is produced as well. This may be oxygen, but
itcould also be carbon dioxide.
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AndersHoveland
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| Quote: Originally posted by woelen | | I tried mixing a solution of potasium iodate in dilute sulphuric acid with hydrogen peroxide. No reaction occurred. Not even on heating.
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You might try using more concentrated acid (>70%). In the case of chloric acid, it becomes much more unstable/oxidizing beyond a concentration of
40%. I think I may have read somewhere that chlorate is not reduced by H2O2 unless the acid is fairly concentrated. (But of course do not use
>90% conc sulfuric acid, since that could obviously potentially oxidize any intermediate iodide to iodine regardless whether any H2O2 was present.
| Quote: Originally posted by woelen | | On addition of the hydrogen peroxide, the liquid lost its brown color, the iodine disappears. A lot of gas is produced as well. This may be oxygen,
but itcould also be carbon dioxide. |
Hydrogen peroxide reduces the halogens [except of course fluorine] to halides if the solution is not acidic. The oxalate is oxidized to
bicarbonate, which serves as the base. The equation that best describes your reaction is probably:
I2 + (2)NaCO3H + H2O2 --> (2)NaI + (2)H2O + (2)CO2 + O2
But in the case of chlorine, the element is reduced to ionic form even if the solution is acidic.
Cl2 + H2O2 --> (2)HCl + O2
[Edited on 18-11-2011 by AndersHoveland]
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woelen
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I have doubts about the reaction in which iodine is reduced to iodide. If that were the case, then remainign iodine should dissolve in the liquid,
forming the I3(-) ion with iodide. What I see though is that the liquid becomes lighter and most of the iodine dissolves, but some solid particles of
iodine remain (I only added a small amount of H2O2). Even on prolonged shaking these particles of iodine do not dissolve. I know from experience that
in a solution of an iodide the elemental iodine easily dissolves, even if the solution contains just a few percent of iodide in solution.
I have the impression that the oxalate plays an important role in the reaction between H2O2 and iodine. But it is not clear to me which role.
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AndersHoveland
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The oxalic acid is acidic. The H2O2 oxidizes it away. Iodine cannot be reduced to iodide using H2O2 while the solution is acidic.
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Panache
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Quite right, my memory failed me, also however was my failure to acknowledge the source of this method, mr wack himself. I had begun to try and find
the series of threads where this had been expressed so as to forward proper acknowledgement but gave up in a fit of apathetic laziness, my apologies.
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AJKOER
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A small point, but the reaction between Cl2 and H2O2, surprisingly to some, can actually produce HClO unless the H2O2 is in excess (I believed in read
this in Watt's Encyclopedia Chemistry on one of the methods for the preparation of HClO):
Cl2 + H2O2 --> 2 HClO
and only with excess H2O2:
H2O2 + HClO --> H2O + HCl + O2
also adding H2O2 to chlorine water also yields HClO (this, I believe, was in a different Volume of Watt's Encyclopedia Chemistry):
H2O2 + ( Cl2 + H2O ) --> 2 HClO + H2O
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