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Although it is not the standard procedure for making iodine solution, I have dissolves pure Iodine granules in Ethanol to produce a brown solution which will produce a positive test for starch by creating a purple color.

I tried to create the same solution with isopropyl alcohol but it doesn't work. The Iodine does not dissolve noticeably, and whatever small amount may be dissolved does not complex with starch.

How does Ethanol dissolve elemental Iodine so well especially compared to Isopropyl alcohol?

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  • $\begingroup$ I'm afraid you did something wrong or maybe used solution with high water content. Iodine dissolves well in organic compounds. $\endgroup$ – Mithoron Dec 9 '16 at 23:09
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    $\begingroup$ It was 70% Isoprop but absolut EtOH. Is that enough water to do it? $\endgroup$ – Joseph Hirsch Dec 9 '16 at 23:43
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While iodine is readily soluble in ethanol and isopropanol, it is only soluble to about 300 ppm in water. I think it's pretty clear that the 30% water in your isopropanol solution was plenty to thoroughly inhibit the iodine's solubility.

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  • $\begingroup$ Diluting iodine solution with water does not reverse the dissolution of the Iodine. $\endgroup$ – Joseph Hirsch Jul 14 '19 at 14:25
  • $\begingroup$ I see that iodine solution is actually KI in water. $\endgroup$ – Joseph Hirsch Jul 14 '19 at 14:27

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