Saturday, 21 April 2012

By on April 21st, 2012 in chemistry, friends, science kits

10:37 – Barbara is working on science kits today. I’m doing laundry and working on the forensics book.

I should learn to trust myself. One of the solutions included in the chemistry kit is a sodium salicylate solution that’s 200 ppm with respect to salicylate. It’s used as a standard in a lab session about quantitative determination of salicylate in urine by the Trinder reaction. (Ferric ions react with salicylate ions–actually, almost any phenolic ions–to form an intense violet complex; the intensity of the color is proportional to the concentration of salicylate in the specimens.)

Unfortunately, that dilute salicylate solution is ideal for mold growth, so we have to add a preservative. As I was making up the solution, referring to the instructions I’d printed months ago, I noticed that they mentioned adding a few crystals of thymol as a preservative. That couldn’t be right. Like salicylate, thymol is a substituted phenol, so thymol should also react with ferric ions. So, I thought, dumping an arbitrary “few crystals” of thymol into the solution would ruin its carefully-measured accuracy.

I’d almost decided to substitute a few drops of chloroform as the preservative, but I decided to check just to make sure. So I added one crystal of sodium salicylate to a spot plate, followed by a drop of iron(III) nitrate. As expected, the violet coloration was so intense it looked almost black. I added one crystal of thymol to a second well, followed by a drop of iron(III) nitrate. There was absolutely no visible change.

I really should learn to trust myself. I don’t remember doing it those months ago, but there’s no way I would have added thymol to a salicylate standard solution without checking. What occurred to me now would also have occurred to me then.

Speaking of organic chemistry, I was talking to Paul Jones yesterday and he mentioned that he’d be grading take-home finals for his organic students. Then he mentioned something about the exam focusing on syntheses. I thought what he described sounded a bit much for first-year organic, so I mentioned that to him. It turns out that Paul isn’t teaching first-year organic this year. The final he was talking about was for his grad students. I told him that was a relief, because I was just thinking about asking him if I could take the final, just to see how much (if any) I remembered. Paul was amused. He said I probably wouldn’t do very well on this final, because the synthesis reactions used hadn’t been invented when I was taking first-year organic 40 years ago. (Take that, old guy!) In fairness, Paul did say that the reactions I learned back when dinosaurs roamed the earth typically actually worked pretty well, while the ones his students were learning were sometimes a bit shaky.

14 Comments and discussion on "Saturday, 21 April 2012"

  1. Miles_Teg says:

    RBT wrote:

    “I really should learn to trust myself. I don’t remember doing it those months ago, but there’s no way I would have added thymol to a salicylate standard solution without checking. What occurred to me now would also have occurred to me then.”

    I think I remember you talking about this. Perhaps you should read your old posts every so often

    As to the term papers, I thought you were going to say that Paul had finally seen the light and moved over to P&I.

  2. eristicist says:

    What about your meticulously-kept lab book? Then again, I guess it’d be quicker to test the thymol, rather than try to find when you originally did it.

  3. SteveF says:

    for his organic students

    AIs are now good enough to take chemistry classes? Where was I when this happened?

  4. SteveF says:

    And why don’t the inorganic students have to take finals? Sounds like preferential treatment if you ask me.

  5. Robert Bruce Thompson says:

    What about your meticulously-kept lab book? Then again, I guess it’d be quicker to test the thymol, rather than try to find when you originally did it.

    Lab notebooks are for recording the details of experimental procedures. I don’t make entries for kit chemicals, other than a running log. For example, if I’m making up two liters of 6 M sodium hydroxide, I should in theory use 239.9826 grams and make up the solution to two liters. In reality, there are issues like purity (what I use might be only 99.4% NaOH), and changes to the chemical itself (it might absorb enough water from the air to cake it, or it might absorb enough carbon dioxide gas to convert some of it to sodium carbonate.) So, what I actually do is log the amount used (which might be, say, 242.08 grams), and the source of the chemical. The solution is 6.0 molar, which means there’s room for a bit of slop on either side. In practice, I’d always use at least 239.9826 grams and err in the direction of going slightly over. When I finish making up the batch, it gets a batch number, which goes on the individual bottles included in the kits. That way, if something happens, I can at least try to figure out what went wrong. So far, no issues.

  6. Robert Bruce Thompson says:

    I’d guess there aren’t a lot of inorganic chemistry majors. When I was in college 40 years ago, a lot of chem majors went on to grad school in organic. Fewer, but still a significant percentage went on to grad school in inorganic, analytical, physical, and biochemistry, probably roughly in that order. Nowadays, I suspect biochemistry and related fields are the most popular, with organic lagging and the others far behind. But that’s just a guess. If Paul reads this, perhaps he’ll comment.

  7. SteveF says:

    Interesting, but your comment shows that I didn’t phrase my joking around very well. I was attempting to form the nucleus of a new grievance movement by suggesting that the AIs didn’t have to take finals.

  8. Miles_Teg says:

    When I did 1st year chemistry in 1976 the P&I labs were huge barn-like affairs, the Organic ones somewhat more intimate. We did a term (8-9 weeks) of physical, a term of inorganic and a term of organic, in both lectures and labs. The lectures and labs weren’t in sync, so we all did P&I for the first two terms and organic in T3. My labs in T3 happened to be organic too but some students had their organic labs in T1 or T2. It would be necessary for the P&I Department to have twice the lab space of organic but it seemed to me that the ratio was much larger.

    And boy, did the Organic Chemistry Department stink! I walked in the door and it was pretty bad. By the time I got to the lab it was really overpowering. I only did one year of it, a pal who majored in Organic (and P&I) said it ruined his sense of smell.

  9. Chuck Waggoner says:

    Yeah. I did well in Chemistry and Physics and the teachers actually got angry that I did not want to continue, but the stink actually de-motivated me to ever want to work in the chemistry field. During a long stretch of my life, my mom taught at a Jesuit-run seminary high school just a couple blocks from the main Eli Lilly drug plant in downtown Indianapolis. I had a car of my own earlier than many other kids, because I was working and needed it to get to work. Occasionally, I would have to drive down to drop off or pick up my mom if her car was in the shop, and the neighborhood stench was awful. The kids she taught always said those days were when they were cremating the mice.

    I made a lot of teachers mad, because I did well in their area, but would not continue with them. Having been on the debate team in high school, the university debate coach naturally thought I would continue while at college. But the university owned a 40,000 watt radio station, so I got my public-speaking practice there, and not from debate.

  10. Miles_Teg says:

    The physics and P&I labs smelt neutral, it was only the organic chem labs that was off. I think they probably have better ventilation nowadays.

    The worst experience for me was cycling between home and high school. I had to pass the SA Rubber Mills – they made tyres and such. The stink from the other side of the road was awful, must have been far worse to work there.

  11. OFD says:

    Mrs. OFD grew up somewhat near paper mills in upstate NY, and those were real special. Currently, during my commute, I can get a whiff on the way in, first of all, of the manure just recently spread over the cornfields again; then the landfill by the highway; and then finally on past Green Mountain Coffee Roasters. The manure ain’t too bad, but the other two aromas can get pretty intense.

  12. BGrigg says:

    Pulp and paper mills have special odor memories for me growing up on the coast of BC. I’ll take the manure over pulp stink every time.

  13. Chuck Waggoner says:

    Huge pig farm between Tiny Town and Indianapolis. Does not matter which route I take–Interstate or farm road–the stink spreads for miles. And we actually eat the stuff that produces that smell.

    Well, unless you keep Kosher.

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