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K12Chemistry
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Separating Iodide and Iodate?
I am trying to make KI by reacting KOH with pure crystal iodine. But when this happens, it reacts to form potassium iodide and iodate. They are both
in solution so does anyone know how i can separate the two.
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woelen
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Use slight excess of iodine, such that the solution remains pale brown instead of colorless after all iodine has dissolved. Now you have 5 parts KI
and 1 part KIO3 with slight excess of I2.
Next, evaporate all of the material. This will give a light brown solid. Heat this solid fairly strongly. The KIO3 will decompose, giving KI and O2.
Excess I2 will be driven off as well (purple vapor). What remains is fairly pure KI.
Dissolve the fairly pure KI in as little as possible water and allow to evaporate such that only a small amount of solution remains over a white
crystalline mass. Decant the liquid as much as possible and put the mass on a filter, which is put on a pile of paper tissues. Much of the adhering
liquid is absorbed by the filter and paper tissue. Rinse the solid with some pure and clean acetone or diethyl ether and let this liquid evaporate.
This treatment will give you quite pure KI. Store in a tightly closed vessel, KI is fairly hygroscopic.
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blogfast25
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Quote: Originally posted by K12Chemistry  | I am trying to make KI by reacting KOH with pure crystal iodine. But when this happens, it reacts to form potassium iodide and iodate. They are both
in solution so does anyone know how i can separate the two.
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Please use the Search Facility: this must be thread #15 on this boring subject!
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Pyro
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or crystallize it. KIO3 isn't nearly as soluble as KI, but MUCH more expensive.
all above information is intellectual property of Pyro.  |
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K12Chemistry
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KIO3 dissolves in KI solution. 
can someone give me an idea as to what temperature i need to heat this to decompose the KIO3 into KI and Oxygen.
Also why would you use an excess of iodine
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MrHomeScientist
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Woelen's method is a great way to make a high purity product. I made a video about making KI from KOH and I2, but was unaware how much KIO3
contamination there was in it. This actually caused one of my other videos to be inaccurate, when I used my product to make iodine using acid but no
extra oxidizer! The KIO3 impurity was enough to create iodine with just the addition of acid, which shouldn't happen. I recently ordered some pure KI,
so once that arrives I need to post a correction video showing all this.
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K12Chemistry
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oh,
I've seen so many of your videos. Big fan!
I didn't know you were on sciencemadness.
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Ral123
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I had no idea iodine can displace oxygen and produce iodate like chlorine does. I though iodine is with reactivity similar to sulphur.
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K12Chemistry
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What about using acetone. Iodate is soluble but Iodide isn't. Would that work?
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woelen
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@Ral123: Iodine does not displace oxygen, the reaction described here is a simple disproportionation reaction. First, iodine is disproportionating to
iodide and hypoiodite. Next, the hypoiodide in turn disproportionates to iodide and iodate. The iodate is decomposed by heat, loosing its oxygen.
Reactivity of iodine is larger than reactivity of sulphur, but in some respect they are similar. Sulphur also can disproportionate in alkalies (it
requires heating and the reaction is slower), but it forms sulfide and thiosulfate as the initial step of disproportionation.
@K12Chemistry: Is iodate soluble in acetone? I doubt this. KI is very slightly soluble, but this solubility is so low that there is no need to fear
great losses when rinsing KI with acetone to get rid of water and impurities.
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K12Chemistry
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oh sorry i meant it the opposite.
KI dissolves in acetone but not KIO3
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K12Chemistry
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Woelen in your method you say to use an excess of iodine, why? couldn't you just heat it.
Also what temperature would it take to decompose the KIO3 to KI. Would a basic hotplate work? Or a spirit burner?
Is there any solution (More or less readily available) that KIO3 is soluble in but not KI, or the other way around?
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K12Chemistry
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I think I have found the answer,
1g of potassium iodide dissolves in 8ml of methanol (pretty soluble), potassium iodate however, is completely insoluble in methanol. You add methanol
to the mixture to dissolve the iodide and filter it. You then boil down the methanol to get a solid crystalline product of pure potassium iodide
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unionised
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If you want KI and not KIO3 then the classic method is to mix the I2 with iron filings and water to get a solution of FeI2
then add KOH to ppt Fe(OH)2 and leave a solution of KI which you can evaporate the water from.
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blogfast25
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| Quote: Originally posted by unionised | If you want KI and not KIO3 then the classic method is to mix the I2 with iron filings and water to get a solution of FeI2
then add KOH to ppt Fe(OH)2 and leave a solution of KI which you can evaporate the water from. |
Interesting tip. Live and learn. Must try that once...
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woelen
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If you use excess of I2, then no KOH remains left. Excess of I2 can be driven off by heating. If you have
excess of KOH, then you get hard to remove impurities which cannot be driven off.
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K12Chemistry
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| Quote: |
If you want KI and not KIO3 then the classic method is to mix the I2 with iron filings and water to get a solution of FeI2 then add KOH to ppt Fe(OH)2
and leave a solution of KI which you can evaporate the water from.
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Sorry guys, I guess I wasn't clear enough in the starting question where I said I wanted to separate the two. What I actually was trying to do was get
pure potassium iodide and probably discard of the KIO3.
Anyway would the equation for the FeI2 method be:
I2 + Fe -> FeI2
FeI2 + 2KOH -> 2KI + Fe(OH)2
Is this balanced?
Sorry I'm a noob so it's probably wrong
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blogfast25
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| Quote: Originally posted by K12Chemistry |
Anyway would the equation for the FeI2 method be:
I2 + Fe -> FeI2
FeI2 + 2KOH -> 2KI + Fe(OH)2
Is this balanced?
Sorry I'm a noob so it's probably wrong
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No, you happen to be right on this one. But I'd like to see practical implementation of this idea, not just balancing equations.
[Edited on 14-4-2013 by blogfast25]
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K12Chemistry
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Yeah I'm going to stoichiometrically calculate how much of each reagent I use, but first I need to find the solubility of FeI2.
Does anyone know the solubility of FeI2 in water?
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K12Chemistry
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To make Iron Iodide:
I2 = 254 g/mol
Fe = 56 g/mol.
So I add about 127g of iodine to 28g of Fe, obviously not on such a great scale.
To make KI:
FeI2 = 310 g/mol
KOH = 56 g/mol
So I add approximately 155g of Iron Iodide to 56g of KOH
Is this right?
If it is then it's actually the first time I've done this all on my own
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blogfast25
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Yes, the math is correct but you would add the KOH to the FeI2.
Presumably one would mix the requisite amount of I2 with an excess of iron filings or steel wool. The excess is needed to complete the
reaction in a reasonable amount of time. Mild heating and good stirring will also speed things up considerably. When the solution contains apparently
no more free iodine, it would be filtered to separate out the excess of iron. The filtrate would contain dissolved FeI2, in the amount
calculated.
Then a calculated amount of KOH (or NaOH, MW = 40 g/mol) solution would be added to the filtrate, to achieve a pH of about 7 – 9. This will
precipitate the Fe2+ as Fe(OH)2 and that is filtered off. The process is known as a 'displacement reaction'.
The filtrate would contain relatively pure KI (or NaI).
Re. the solubility of ferrous iodide, iodides are generally very soluble and so are ferrous compounds. Chances are that ferrous iodide is very water
soluble.
[Edited on 14-4-2013 by blogfast25]
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K12Chemistry
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I thought steel wool wasn't pure iron
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K12Chemistry
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oops just searched it, about 98% iron.
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blogfast25
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No, it's not pure but it doesn't really have to be.
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AndersHoveland
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| Quote: Originally posted by Ral123 | | I had no idea iodine can displace oxygen and produce iodate like chlorine does. I though iodine is with reactivity similar to sulphur.
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Iodine seems to act more like the other halogens in the presence of water.
But much like sulfur, the covalent bond between iodine and hydrogen is very weak.
[Edited on 15-4-2013 by AndersHoveland]
I'm not saying let's go kill all the stupid people...I'm just saying lets remove all the warning labels and let the problem sort itself out.
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