Day: September 4, 2014

Thursday, 4 September 2014

08:08 – Being a chemistry geek, I get excited about things that other people don’t even notice. For example, yesterday I was making up solutions for kits. One of the solutions I made up was the IKI (iodine/potassium iodide) solution (Lugol’s solution) that’s included in most of our kits.

Iodine is extremely insoluble in water, something like 290 mg/L (290 ppm) at room temperature. Potassium iodide, on the other hand, is extremely soluble in water, something like 1,400 g/L at room temperature, or almost 5,000 times more soluble than iodine. The interesting thing is that iodine is very freely soluble in solutions of iodide ions, and the more concentrated the iodide solution, the faster the iodine goes into solution.

In the past, I’ve made up two liters of IKI solution by dissolving 40 grams of potassium iodine (KI) in about 400 mL of water, adding 25.4 grams of crystal iodine, swirling the bottle periodically over the day or so that it takes the iodine to go into solution, and then making up the solution to two liters. Yesterday, I decided to see if I could speed things up a bit by using much less water initially.

So weighed out 40 g of KI and transferred it to a 125 mL bottle. Ordinarily I’d have added some water at that point to dissolve the KI, but instead I weighed out 25.4 g of iodine crystals and added them to the bottle, right on top of the solid KI. Before I had time to add any water, a reaction started. A solid-state reaction, in which the solid molecular iodine started to react with the solid potassium iodide, producing essentially potassium tri-iodide in solid form. I could actually watch the reaction progress, starting with a bottom white layer of KI and a top dark-gray layer of iodine crystals. The two layers began to merge into a single dark brown layer.

I watched that happening for a few seconds and then added 60 mL of so of distilled water and capped the bottle. I inverted the bottle several times to mix the contents and all of the solids went into solution almost instantly. Because dissolution of KI is endothermic, the bottle quickly became quite cold. Even though the air in the house is air conditioned and dehumidified, water vapor immediately started condensing on the surface of the bottle and running down the sides. This whole process is fascinating in so many ways: kinetically, thermodynamically, and enthalpically. It’s good to be a geek.

11:55 – A few years ago, Barbara literally knocked over a hornets’ nest while she was working in the back yard. She was stung badly, and she’s understandably afraid of hornets and similar stinging insects. A week or so ago, she mentioned that there was a nest of yellow jackets or hornets down at the back of our property, apparently inside the trunk of a tree. So I walked down there after dark that evening and took along a can of hornet/wasp killer. One of those that shoots a stream instead of a fine mist. I walked over to where I’d seen the bugs clustering earlier that day, and hosed it down with the hornet/wasp killer. They immediately swarmed out of the nest, but I turned off my flashlight and walked away unstung. The next day, I noticed there were a lot of dead bodies lying near the nest entrance, but there were still a lot of them swarming around. So I went down again that night and sprayed again. The next day, same deal. I got some of them but there are a lot left. I understand that nest may be buried deeply and contain literally thousands of the things.

If I were living in an Agatha Christie novel, I’d use something that actually kills them, like potassium cyanide. A couple tablespoons of that in the nest entrance and a bit of sulfuric acid would fumigate the hell out of that next. I have both of those in my lab, but I think I’ll take a more traditional approach.

I search the web for stinging insects in North Carolina, attempting to identify the species, but I haven’t gotten a close enough look at one to be sure. There are several candidates, and the advice for all of them on the NC Ag Extension web site is similar. First, just leave them alone unless they present a real threat to people. Second, if you have to kill them use something like the Spectrocide/Hot Shot insect spray I used, following the label directions strictly, of course. But the site warns that it probably won’t be effective and even several treatments may leave a viable nest. It does say that the colony dies out in the winter and is seldom re-used the next year.

The site also says whatever you do, don’t use gasoline because it’s harmful to the environment. I take that to mean that gasoline will in fact kill all of the little SOBs but using it would violate federal law. Federal law, of course, ignores the fact that these stinging insects are very harmful to our environment. I’m thinking napalm.

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