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Topic: Mixed iodine/KI recrystallised from petroleum ether  (Read 8224 times)

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Offline limpet chicken

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Mixed iodine/KI recrystallised from petroleum ether
« on: February 09, 2005, 12:30:29 AM »
I had just been doing a little experiment on seperating iodine from tincture.

The tincture is the common one sold for disinfecting wounds, and contains around 2-3% iodine, and a similar amount of potassium iodide, along with water, and ethanol as co-solvent.

I shook a small amount with pet. ether, siphoned off the solvent, and left the tincture layer, with a small surface film of naptha to evap, the tincture went considerably thicker and more tenaceous than it usually appears, then evaporated slowly, over the course of a day without heat.

Perfect square crystalls have formed in the half-lightbulb I used as an evaporating glass, they are square, perfect in dimension, of perhaps one millimeter in diameter and half, to a quarter millimeter thick, all of uniform size, and have concentric smaller square depressions within, kind of reminiscent of a CPU chip in appearance, and of the
typical dark violet-black color of iodine.

I have seen iodine in two forms, the stuff I have in a vial in large quantities, bought comercially, is in the form of the typical lustreous dark indigo flakes, and is resublimed I2, and the other form I have seen, was in large 1-2cm large curls, consisting of tightly packed, but very tiny individual crystals, of a silver-gray color not far off from powdered telllurium or the gray allotrope of selenium, this was heat-distilled at ambient pressure from tincture, and not resublimed, at the time of preperation, I was about 10 years old, and did not realise iodine was volatile, and it was greatly more volatile than the flakes, subliming away into the atmosphere completely within hours.

Does the recrystalised combination of I2/KI usualyl form these perfect crystals?

I wish to preserve them in as much detail as I can, as they are rather attractive to look at, and for posterity of my experiments, can anyone suggest a way I could do this, without storing in water, which would destroy the crystal shape, by dissolving away the KI, and traes of the I2?

Thanks.
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Offline Mitch

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Re:Mixed iodine/KI recrystallised from petroleum ether
« Reply #1 on: February 09, 2005, 01:12:10 AM »
For future reference, the other boards such as "physical chemistry" are only meant for students in a physical chemistry class that have a physical chemistry question. Most posts other than that belong either in the random science board or this one.

Anyways, the crystals are most likely the naphthalene that you added.
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Offline limpet chicken

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Re:Mixed iodine/KI recrystallised from petroleum ether
« Reply #2 on: February 09, 2005, 01:49:29 AM »
Sorry Mitch, I didn't realise that, I will keep such posts to the citizen chemist/random question form now I know :)

There was no napthalene added, by naptha, I was referring to petroleum ether.
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Offline AWK

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Re:Mixed iodine/KI recrystallised from petroleum ether
« Reply #3 on: February 09, 2005, 06:54:20 AM »
I think it is better to destroy all KI using an oxidiser, eg diluted water peroxide in acidic media and crystallize the whole content of iodine from the tincture.
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