hodges
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KIO3 From KI
I want to do a clock reaction but it requires potassium iodate. All I have is potassium iodide. Is there any way to produce potassium iodate from
potassium iodide? Alternatively, does anyone know of a similar clock reaction using just KI or I and some reducing agent?
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BromicAcid
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The reactivity series for the halogens is reversed in the oxoacids. Maybe if you had some sodium chlorate you could add it to a solution of potassium
iodide, you should get some sodium iodate and potassium chloride precipitate. Then add more potassium chloride to precipitate out the iodate as the
potassium salt.
Also to consider is electrolysis although it is more energy intensive then the production of chlorates I believe.
Or you could reduce the iodide ion to iodine and then oxidize that using the various methods to produce iodate from iodine.
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unionised
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I suspect that you could oxidise iodide to iodate with bleach (which is cheap). Since the solubillity of KIO3 is low you should be able to precipitate
it from solution with almost any K salt you happen to have about the place. (KCl is the cheapest example here in the UK)
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Polverone
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"[Iodine] is soluble in a solution of caustic potash, a dilute solution most probably containing the hypoiodite, which, however, changes slowly
into iodate, the change taking place rapidly on warming."
(from 1911encyclopedia.org)
That sounds like "add iodine to warmed KOH solution" to me. The iodine is of course easily liberated from KI solution by gassing it with
chlorine or acidifying and adding H2O2. Filter the precipitated iodine and use it to make your iodate fairly quickly. When freshly precipitated,
especially, iodine will sublime rapidly at room temperature.
I'm afraid that adding bleach to KI might convert it to iodine; maybe not.
PGP Key and corresponding e-mail address
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hodges
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| Quote: | Originally posted by Polverone
I'm afraid that adding bleach to KI might convert it to iodine; maybe not. |
It does; at least in acidic solution. It sounds like preparing I this way and then washing and reacting with KOH might work though.
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hodges
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Alternate Reaction
I found another clock reaction on the internet that just uses KI (instead of KIO3). I got a modified version of this to work quite easily.
I took just a few small crystals of KI and put them into a test tube half full of water. I added about a ml of 3M HCl, and then I added some starch
solution. The solution was clear.
I added 5 drops of 3% H2O2 from the grocery store and the solution turned dark blue. I then added a couple of drops of solution made using Kodak
photo fixer. The experiment called for Na2SO3 which is a reducing agent, so I figured the fixer (mostly Na2S2O3) would also work. It did, and the
solution became clear. After a couple minutes it suddenly turned dark blue again. I was able to repeat the reaction numerous times by adding more
thiosulfate to temporarily make the solution clear. Depending how many drops I added, I was getting delays of seconds to several minutes. Very
impressive, especially considering that only a few cents worth of chemicals were needed.
The sulfite or thiosulfate reacts instantly with any free iodine in the solution to change it to iodide. In acidic solution, H2O2 changes iodide to
free iodine, but at a slow rate. The solution stays clear as long as there is any thiosulfate present because the thiosulfate consumes the iodine as
fast as the H2O2 can produce it. Once the thiosulfate is gone free iodine quickly appears and reacts with the starch to turn the solution blue.
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unionised
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Glad you found a way round the lack of iodate. Have you heard about this one?
http://staff.science.nus.edu.sg/~parwani/c1/node65.html
It oscilates, very odd for a chemical reaction.
Given that you wanted to make iodate from iodide and that, in acid conditions, iodide will destroy iodate, I wonder why you thought that acid
conditions would be relevant to attempting to make iodate.
Bleach is alkaline. In alkali, iodine will convert rapidly to hypoiodite and then slowly to iodate. If the bleach oxidised iodide to iodine then it
would subsequently be converted to iodate. (More rapidly if you heated it).
The problem with disproportionating iodine to get iodate is that most of the stuff gets converted to iodide. Adding an excess of an alkali and an
oxidant would get round this. Bleach is a cheap an easy way to provide both.
[Edited on 22-2-2004 by unionised]
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hodges
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Actually, what I was trying to say is that hypochlorite produces I from KI under acidic conditions, as I have done this reaction before. My idea was
to filter the iodine formed and then react this I with KOH. Afterwards I would heat that to get KIO3.
Thanks for the link to the oscillating reaction. I also ran across a link where the necessary chemicals for this reaction can be bought for under $10
in case anyone else is interested:
http://www.stevespanglerscience.com/product/1242
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Mephisto
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Iodates from iodine
For those, who are still interested in the synthesis of iodates and iodic acid. Iodic acid HClO<sub>3</sub> can be synthesized this way:
I<sub>2</sub> + 5 H<sub>2</sub>O<sub>2</sub> --> 2 HIO<sub>3</sub> + 4 H<sub>2</sub>O
Short description: 50 g I<sub>2</sub> + 50 ml conc. HNO<sub>3</sub> + 25 ml 30%
H<sub>2</sub>O<sub>2</sub> + 50 ml H<sub>2</sub>O; heat to 70°C in a water bath; let the water evaporate and
HClO<sub>3</sub> crystals will precipitate.
BTW: Iodic acid could be used for the Landolt reaction, so it's not necessary to convert it into its potassium salt.
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