craynerd
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Solubility of iodine in water ...?
Guys
I was going to show the reaction between zinc and iodine, dissolving a known mass of iodine in water, add a known mass of zinc, calculate amount of
zinc reacted (therefore zinc in excess) and from here show calculations of empirical formula.
However when I saw the method I was confused as my understanding is that iodine is only sparingly soluble in water, thus dissolving 1g in 25ml of
water was going to be a challenge! I refused to accept the method and disregarded the experiment. However, I have since found that once a small amount
of iodine is dissolved in the water, adding the zinc liberates iodine ions which assist the remaining iodine to dissolve through the formation of the
tri-iodide ion.
Now i`m afraid I have just recalled this from a resource on the net and I don`t understand it. Could someone please explain why the rest of the iodine
dissolves or point me somewhere where I can learn?
Cheers
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bio2
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FYI I2 dissolves 0.029 g @ 20 deg and 0,078 @ 80 deg
per 100cc water per CRC 74th edition.
Iodine element does dissolve in solutions containing iodide to
a much greater extent.
You may want to perform your experiment in EtOH as I2 is
much more soluble 20.5g @ 15deg or MeOH 23g @ 25 deg
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woelen
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Add a little KI in advance and then add the iodine. For each iodide ion, one molecule of I2 goes in solution, and then that can react with zinc,
giving even more iodide in solution, making the dissolving of I2 more and more easy.
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Pyridinium
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How about this. Leave the iodine crystals in the water to equilibrate for a few days so they form a saturated solution. Leave the I2 crystals in the
bottom. Then put some zinc turnings in there and leave the container covered for, say, 6 months.
If the Zn reduces I2 to I-, and the production of I- helps solubilize more I2 (which it will), then you should be able to demonstrate a sort of
positive feedback system. Over a long enough time the I2 should slowly go into solution with the help of the Zn.
Even though zinc is not soluble in water much, it doesn't have to be. The reduction of species in solution by metallic zinc happens at the metal
surface if I understand correctly. A very common procedure is to boil aqueous solutions with Zn metal.
So... let us know how this works for you.
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