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rstar
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[*] posted on 5-10-2011 at 19:04
What is produced in reaction of I2 and K2S2O5


Hi Geeks,
What is the produce of reaction between iodine and Potassium metabisulfite (in a water solution) ???



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[*] posted on 5-10-2011 at 22:14


Metabisulfite is unstable in aqueous solution and reacts with water to form hydrogen sulfite:

K2S2O5 + H2O → 2 KHSO3

Potassium hydrogen sulfite and iodine then undergo a redox reaction to yield potassium hydrogen sulfate and hydroiodic acid:

KHSO3 + I2 + H2O → KHSO4 + 2HI

This is more or less the expected reaction in acidic aqueous solution. If you hope to end up with potassium iodide a basification (KOH or other potassium base) is needed to convert HI to KI. It should also be noted that HI is a weak acid and a fair share of it leaves the solution rather than dissociates, lowering the yields.

[Edited on 6-10-2011 by kavu]
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[*] posted on 5-10-2011 at 23:20


Quote: Originally posted by kavu  
It should also be noted that HI is a weak acid
[Edited on 6-10-2011 by kavu]


Thanks for the equation, and HI is not a weak acid, it is very strong acid, even more stronger than HCl :o



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[*] posted on 6-10-2011 at 03:14


Quote: Originally posted by rstar  
Quote: Originally posted by kavu  
It should also be noted that HI is a weak acid
[Edited on 6-10-2011 by kavu]


Thanks for the equation, and HI is not a weak acid, it is very strong acid, even more stronger than HCl :o


I guess it helps to define 'acidity' and what one think of as a strong acid. I could argue both cases for HI.



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[*] posted on 6-10-2011 at 11:43


Quote: Originally posted by Panache  
Quote: Originally posted by rstar  
Quote: Originally posted by kavu  
It should also be noted that HI is a weak acid
[Edited on 6-10-2011 by kavu]


Thanks for the equation, and HI is not a weak acid, it is very strong acid, even more stronger than HCl :o


I guess it helps to define 'acidity' and what one think of as a strong acid. I could argue both cases for HI.

Any of the conventional definitions will mean that you lose the argument. A definition that makes HI look like a weak acid (in water) will get laughed at.
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[*] posted on 6-10-2011 at 12:11


HI is undoubtedly a strong acid in aqueous solution with a staggering pKa of -10 at room temperature. It was purely my mistake to mix HI and HF :)
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