Chemical Treasure Hunt Part II

I have written previously about our work identifying the contents of Blists Hill Victorian Pharmacy Jars (http://www.possibilitiesendless.com/?p=931), and we’ve pretty much solved the riddle of the jars. Briefly this Victorian Pharmacy exhibit has many jars filled with either the original and sometimes labelled contents, but possibly also poorly documented replacements made by well-meaning curators over the years. The last post described some rather Victorian chemistry to confirm the presence of mercury in a sample.

Since that work in January, we’ve largely finished off the riddle of the jars, my colleague Jane Essex and various volunteers (undergrads, ChemNet students, local school students) did amazing work a few weeks ago figuring it all out. Some surprising contents included cochineal beetles (identified when someone accidentally squished one and saw the characteristic colour), modern indigestion tablets, and a lot of food dyes – you’ve got to have the coloured solutions if it’s chemistry, right?

How do you go  about identifying a complete unknown? Well the first step is usually to figure out if there’s anything likely to give a flame test result in it. Flame tests are straightforward to carry out, don’t use a large quantity of material and pretty much confirm the presence of metal ions by characteristic colours. Sometimes the name on the jar gives a clue – it might be an old name for something readily identifiable, it might be exactly what it says on the tin or it might not be. In any case, it’s a starting point and that’s better than nothing. After flame tests (and you can often figure out things like sugars by the way they burn as well), the next tests really depend on where you think it’s going. If it is a brightly coloured solution with no flame test results, chances are you’ve got a food dye and you’re heading for UV/Vis analysis. If it’s a white powder and you’ve got a flame test result, the hunt for the counter ion begins. Suspected sugars are also easy enough to test for. The real challenge comes in those clear, colourless liquids that may, at some point, have contained some extract in water or water-ethanol mix. So maybe you dry the sample down and analyse the residues, perhaps you go high tech with NMR or IR.

The real joy of this work, and the reason that it will be appearing in our undergraduate laboratories this coming year, is that it is genuinely open-ended problem solving. One common comment on feedback from participation in our analysis days is that they would have liked it if someone could have told them they were correct or not. You can’t just give up on this chemical puzzle, and satisfaction with the answer is intrinsically linked to your own ingenuity in figuring out what tests to try next. This is not the sort of problem based learning where the students can slack off and wait for the answers (or if it’s one of those open educational resources, simply google the answers). The plan for our undergrads is to get them to identify some unknowns in the laboratory. We’ll be kind and give them a recipe book of possible tests but points will be awarded for identification in the fewest number of tests. I may not be kind to the demonstrators however – I don’t want the students to be told the answer, or be given hints. It’s quite possible that I may get a colleague to make up the unknowns and keep the identity key hidden from all of us. No peaking, no prompting, proper problem solving.

The second type of activity that will hit the undergrad lab, this time in the form of group projects, will be analysis of ‘proprietary’ mixtures. These were often created by pharmacists and designed to treat anything (and likely nothing). We did one a few weeks ago that was essentially oil in water/ethanol. These require a little more sophistication than  a handful of tests from the recipe book – they often have organic components and water soluble components that need to be identified. A simple example would be a herbal extract (something like eugenol) in an oil-water emulsion. Identifying all the components could be quite a challenge. So I get to do some research into these proprietary mixtures this week and make a few up for the students to get their teeth into.

If anyone’s wondering why we’re making up samples rather than just finding another pharmacy that wants some analysis done, I feel it’s fairer for assessment for there to be a defined if undisclosed answer. There’s also the pressing issue of risk assessment, we can have enough demonstrators around for an analysis day, it’s a bit harder during term time. We’ll call this a pilot study year to see how these activities work in the lab class and look to develop it further next year.

 

One thought on “Chemical Treasure Hunt Part II

  1. If you’ve got unidentified solid, why not try powder diffraction?
    I imagine most of the salts have fairly small cells, that can be indexed reasonably easily, and once you’ve got a cell a quick search of the CDS will tell you what you’ve got. And if you’ve got an idea already, you can confirm it very easily. For example, the structure of Diamminemercury chloride is known, so you could not only check for Hg, NH4 etc. but also determine the stoichiometry.

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