Anomalies or Inexactitudes?

The main reason we do concurrent laboratory sessions with our science courses is to reinforce the (largely theoretical) material presented in the lecture with hands-on observation-based laboratory experience. Truly, it is a delight to talk with authority about a reaction that I, myself have actually performed in lab. It is even more wonderful to talk about a reaction or a physical phenomenon that class has as a shared experience in order make a “textbook” description come alive. Sometimes, experiments “backfire” in their attempt to corroborate textbook knowledge. There are three sources of disparity from experimental and literature results. One is of course, the experimenters lack skills to perform the experiment well. If a normally high yielding reaction, only produces 0.1% yield at the hands of a student it is likely due to poor technique. Another is the limitations of the experimental methods. If a product is not adequately purified or dried its melting point will not coincide with the literature value of the pure compound. Chromatograpy techniques such as TLC are notorious for giving erroneous information on product identity and purity. Finally, it could be that experience does not line with theory because the theory has been presented in an oversimplified manner in the textbook so that it does not really accurately reflect what is achievable in the laboratory. Anomalies and inexactitudes should be a path for future investigation and not written off as a “failed” experiment. This is a good argument why certain experiments should be revisited over the curriculum as student skill and understanding of laboratory techniques develops.

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One Comment

  1. Posted November 12, 2009 at 9:40 am | Permalink

    I remember you said this to me! I didn’t mess up last week’s H2O2 decomposition lab–the procedure did not take into account heat lost in an open system and that the ‘literature value’ didn’t state what temperature and pressure that was calculated in. (So would that fall under the ‘experimental methods’ or the ‘theories being over simplified’ category?)

    But the fiasco with the percent recovery in the copper lab, yes that was all me. =)


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