Sunday, 22 January 2012

By on January 22nd, 2012 in science kits

11:39 – While she was watching basketball yesterday, Barbara finished packing and labeling 60 each of five groups of solids: amoxicillin capsules, ascorbic acid tablets, dextrose, lima bean seeds, and carrot seeds. She’ll finish up agar and Rhizobium innoculum today.

I took a break from writing to do some stuff in the lab. I wanted to have several solutions ready for packaging after deadline. Unfortunately, some stuff doesn’t go into solution very quickly. For example, even with constant agitation and warming, copper(II) sulfate takes a long time to dissolve. I make up one molar solutions of that for the chemistry kits, which is about 500 grams of the pentahydrate dissolved and made up to two liters of solution. I finally gave up trying to get the stuff to dissolve faster. Now, I just transfer 500 grams of the salt to a clean two-liter soft drink bottle, fill it up most of the way with distilled water, and just invert the bottle a few times any time I think about it. It takes several days to a week for the salt to dissolve completely.

Some stuff that goes into the biology kit worries me a bit in terms of dissolution speed. One of those is Sudan III stain. Some vendors sell what is supposedly a 1% solution of Sudan III in isopropanol. I’m not sure how they do that. The best figures I can find say that Sudan III is soluble only to about 0.2% in alcohol, and nearly insoluble in water. (That’s certainly true; adding a tiny amount of Sudan III powder to some water yields a barely pink solution with undissolved solid on the bottom of the container.)

Anyway, some of these vendors include images of the bottle, which makes it very clear that the concentration is nowhere near 1%. Here, for example, is the Home Science Tools page for Sudan III. The stuff is pinkish orange in this image. According to the MSDS, the solution is 1% Sudan III in 99% isopropanol. I don’t see how that’s possible. The best I can do is about 0.2% in 99% IPA.

And isopropanol isn’t the best choice of solvent for Sudan III. A better choice is 50% acetone, 35% IPA, and 15% water, by volume. Conveniently, that means a 1:1 mix of acetone to 70% IPA. So I just went down to the lab, measured 500 mL of acetone into a clean one-liter soda bottle, and added 2.0 grams of Sudan III powder. The solution was immediately intensely colored blood-red, and opaque even when I held the bottle up to the light. I made up the solution to one liter with 70% IPA, at which point it was still so intensely colored that it was opaque to direct light. And, not all of the Sudan III had dissolved, although I had to invert the bottle and look at the powder still in the bottom to see that dissolution was not complete. It’s possible the remainder will go into solution over time, but it doesn’t really matter to me. I’m labeling the Sudan III bottles in the kit as “saturated” rather than with a percentage. That means all I need to do is keep some Sudan III powder visible in the bottom of the stock bottle. When I need more stain solution, I can just add more 1:1 acetone:IPA to the bottle and make sure there’s still undissolved solid present.

14 Comments and discussion on "Sunday, 22 January 2012"

  1. brad says:

    “acetone into a clean one-liter soda bottle”

    I could have sworn that acetone would dissolve an ordinary soda bottle! I have certainly made the mistake of pouring it into a common plastic bottle and having the thing start to “melt”…

  2. Robert Bruce Thompson says:

    It was probably an ABS or PVC bottle. Acetone is death on those. PET (soda bottles) has very good resistance to acetone, but PE resistance is excellent. Still, I just went down to the lab and transferred the stain solution from the PET bottle to an HDPE one.

  3. Roy Harvey says:

    Anyone living far enough north with a clear sky tonight might want to take a look for any auroras.

    HIGH-LATITUDE AURORAS: The Arctic Circle is alight with auroras following this morning’s CME impact. Incoming reports from Russia, Denmark, Scotland, England, and Norway confirm a bright apparition underway now.

  4. Miles_Teg says:

    RBT wrote:

    “Unfortunately, some stuff doesn’t go into solution very quickly. ”

    Unfortunately, I’ve forgotten a lot of the chemistry I once knew. If you eventually get something into solution (or some percentage into solution) and then put it in the cupboard will some or all of it precipitate out again?

  5. Robert Bruce Thompson says:

    Not unless the solution is saturated and the temperature changes.

  6. OFD says:

    Roy, we occasionally see the northern lights from here in northern Vermont on clear nights, and for sure, we some clear nights recently, with temps 10-15 below zero. Saw some shimmering on the horizon but didn’t stay out long.

    We also get a good view of the Perseids in late summer here.

  7. Miles_Teg says:

    I bet you don’t get a good view of the Southern Cross… 🙂

  8. OFD says:

    No need to bet, sir. You is on the other side of the planet and no doubt see many interesting things we do not see, and vice versa. I would bet, however, that you get to see more bare flesh of feminine pulchritude this time of year than I get to see over a decade up here. Outside, that is.

  9. Miles_Teg says:

    When I look at the Northern Hemisphere sky at night I just see a mess of stars that are completely unfamiliar. And the sun is in the wrong part of the sky, so I often confuse East and West when I’m there.

    Yes, the scenery is very nice here at the moment, whether watching the Australian Open or just walking around central Canberra. Unfortunately, due to Global Cooling ™, there isn’t as much to see as I’d like. We’ve had some hot days here but mostly it’s been a bit on the cool side. I’ve had to turn on the electric blanket several nights recently. Brrrrr.

  10. OFD says:

    Perhaps you might persuade some of that very nice scenery to keep you warm on those terribly frigid nights in Oz. I weep crocodile tears for you, sir, having just been through several nights here at 15 below zero. And the only scenery being pine trees, snow, ice and mummified frozen sunflowers and burdock.

  11. Miles_Teg says:

    I’d be happy for them to keep me warm but it’s almost certain that they’d want to have their wicked way with me, and I hate saying no to women.

  12. OFD says:

    In my experience with women of all ages, they do not hear that word anyway.

  13. BGrigg says:

    Yet they often speak it…

  14. OFD says:

    True, that, sir. True, that.

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