Monday, 30 April 2012

07:35 – We’d be ready to build more chemistry kits, except for one thing. Each kit includes a 30 mL bottle of 0.1 M IKI (iodine/potassium iodide) solution. I’m now waiting for iodine to dissolve.

Iodine is very poorly soluble in water, something like 300 mg/L at room temperature. That changes if iodide ions are present in the water. Molecular iodine–a neutral molecule made up of two iodine atoms–reacts with an iodide ion to form a triodide ion, which is extremely soluble in water. IKI solutions contain iodine and iodide ions in water, with the iodide ions typically in at least small excess. The solution we supply is 0.1 molar with respect to both iodine and iodide, which means there’s no excess iodide. That solution is made up of 12.69 grams of iodine and 16.60 grams of potassium iodide per liter.

The problem is, iodine is tightly controlled by the DEA because it’s used by illegal methamphetamine labs. I do have some on hand, but I try to reserve it for situations where I really need elemental iodine. Accordingly, I’ve been buying an IKI solution from one of my vendors that contains 22 grams of iodine and 40 grams of potassium iodide per liter, then adding iodine crystals to bring it up to equimolar, and then diluting to give an IKI solution that’s 1.26% iodine and 1.66% potassium iodide. But iodine dissolves very, very slowly in that 2.2%/4% solution. By “slowly” I mean a week or two with frequent swirling. So, right now, there’s a one-liter volumetric flask sitting on my lab bench with a few grams of undissolved iodine sitting in the bottom. Fortunately, I already had some of the IKI solution made up, but not enough for 30 kits. So I’ll probably bottle that and make up how ever many kits that IKI solution will cover.

The really annoying thing is that although iodine dissolves very slowly in a dilute KI solution, it dissolves quickly in a concentrated KI solution. If I were making up this solution from scratch, I’d dissolve 16.60 grams of potassium iodide in about 20 mL of distilled water and add 12.69 grams of crystal iodine. The iodine would go into solution within a few minutes.

In fact, I think that’s what I’ll do. The stuff in the volumetric flask, when it finally dissolves, can be used for the next batch of kits. It’s not like anything is going to be growing in a 1.26% solution of iodine. And as to my supply of crystal iodine, I may just do what someone suggested a week or so ago. Order it on eBay. I see that there are several vendors offering ACS Reagent grade iodine crystals in 250 g or 500 g bottles for reasonable prices.