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.

MACTLAC 2009

The 2009 meeting of the Midwest Association for Chemistry Teachers at Liberal Arts Colleges (MACTLAC) was held at Hope College. The theme this year was “Integration of Research into Teaching: Improving Learning Through Research.” Plenary sessions were led by Lorna Jarvis (Hope), Nancy Kerner (U of MI), and Don Wink (UIC).  Of most interest to me were the opportunities for inquiry and research rich experiments to be included in the undergraduate laboratory experience. Nancy Kerner (Author of “Guided Inquiry Experiments for General Chemistry: Practical Problems and Application”) mentioned in her presentation that U of MI general chemistry students compile and analyze their data as part of the lab report. The compilation and analysis of class data is a topic that I have discussed in previous posts. Don Wink’s presentation on the Center for Authentic Science Practice in Education (CASPiE) reported on the continuing success of this project to introduce real-time research activities into first and second-year laboratory courses. An interesting aspect of the CASPiE approach is that even though a CASPiE project does displace several topic-appropriate experiments that reinforce class subject material, the student’s academic performance does not seem to suffer because of that. All in all, there are many resources available for instructors to use inquiry and research-rich laboratory materials even if they do not want to completely overhaul their curriculum.

The Prelab: A Mechanism for Student Feedback

Grading lab reports this week I was disconcerted that so many of the students had problems with the calculations required of the lab (EDTA Titration of Zinc Chloride). The lab manual gave a detailed example of the calculations and the prelab was almost entirely composed of step-by-step calculations that were completely analogous to those required by the actual lab. In my mind, the real focus of the lab report should be interpreting the student’s data and comparing with the class – not trying to figure out how to do the math required by the experiment. This semester, I am checking each student’s prelab at the beginning of lab and having them hand it in with the lab report to be graded the following week. Checking the prelab at the beginning of lab allows me to check up on each student with a moment of personal interaction which is a good thing. On the other hand, they are getting the lab set up and the prelab check is more-or-less of a distraction. Another possibility would be to go over the prelab in detail at the beginning of the lab period. This is tempting, but not a very efficient use of time – the right lesson but the wrong time. In Organic Chemistry, I would have them hand in the prelab before the lab so I could grade it and return it to them before the lab report was due.

A 3 Hour Experiment or 3 Hours of Scheduled Lab?

One questions most asked by students about Organic Chemistry lab is, “Will this take long?” Truthfully, I am always tempted to reply, “What does your schedule say?” I suspect that students ask this because they know that a science lab might be significantly shorter than the scheduled time. I take it as a personal challenge to fill the three hours of time each week that I have been allotted. However, even after all my experience teaching, I still struggle with predicting how long a particular laboratory exercise will require. I call it a struggle because I would really like to make the most of lab time without disrespecting students by deliberately going beyond the scheduled time. There are some consideration though: does a three hour lab mean that the average student will be done in three hours or does it mean that the slowest student will be done in three hours? I have to say that, since I started out teaching with smaller class sizes, letting a student stay and extra half-hour to hour to finish an experiment did not really bother me. Now, that labs are full to capacity, accommodating careful students gets to be more problematic. Should I kick them out? Make them come back at another time and finish? I have so far tried to resist making my experiments progressively shorter so that everyone is sure to finish.

The Organic Chem Lab Survival Manual

“The Organic Chem Lab Survival Manual, A Student’s Guide to Techniques” by James W. Zubrick is now in its 7^th edition (2007). Zubrick authors a 368 page paper back that covers most all of the basic laboratory techniques students learn in Sophomore Organic Chemistry. I have used it as a supplemental text in Organic Chemistry for years. Usually, I put a few copies on reserve in the library so students can take a look at it. If students like it enough, they can buy a copy for themselves. Most of the subjects covered are very basic: how to work a separatory funnel, how to perform a recrystallization, and how to pipette a liquid. Zubrick offers a wealth of practical information on all these basic techniques. I think it is a great resource for a student who wants to come into lab prepared to perform a technique correctly the first time. Let’s face it, a lot of lab techniques are learned by trial and error. And that is not necessarily a bad thing, especially for kinetic learners. Those who appreciate other modes of learning can avail themselves of published lab manuals, videos, and listening to the professor’s prelab lecture. Let me offer a note about Zubrick’s distinctive style. I think his style of writing mildly humorous, but some may be put off by his sarcastic comments. My favorite quote (from the distillation chapter): “It is important that the tubing connector remain open to the air; otherwise, the entire apparatus will, quite simply, explode.”

The Dynamic (Organic) Chemistry Laboratory Part II

4) Ongoing investigations replace repeated experiments. It has been customary to repeat the same student experiments year after year without any acknowledgment of past or future experience with the experiment. However, in the dynamic chemistry laboratory, experiments can be performed focusing on the same technique(s) but instead of simply repeating last year’s work the previous year’s results can be used as a starting point to extend the knowledge of an experimental topic. For example, the traditional “banana oil” (isopentyl acetate) experiment can be easily extended to any Fischer Esterification reaction of a primary or secondary alcohol with an appropriate carboxylic acid. Therefore, we have done Fischer Esterification with simple alcohols and o, m, and p toluic acids.

5) Continued analysis of student products. In some cases student products lead to further avenues of investigation that can be pursued “offline.” For example, the phenylmagnesiumbromide Grignard addition to the positional isomers of methylcyclohexanone creates an unequal distribution of diastereomers. Resolving the mixtures and interpreting the results can lead to a long term investigation that goes beyond the week-to-week time frame that is imposed during the semester. More open-ended experiments open new avenues of investigation for both instructor and students. Course laboratory work is a great jumping off point to get students involved in individual research projects.

6) Repeat an experiment the next week. Our example of this one is to perform the extraction of caffeine from tea one week, and do the extraction of caffeine from energy drinks the next week. Students use their experience the first week to design a similar experiment the following week. This follows a familiar research pattern of mastering a “literature” procedure in order to build skills to perform an original research project related to the literature procedure. Certainly, an important function of the course laboratory is to introduce and practice new experimental techniques. However, once a technique is established, it can be extended to encompass an original research avenue.

The Dynamic (Organic) Chemistry Laboratory Part I

1) Instead of one single experiment repeated by all the students, three or four different variations of the same experiment can be performed by different students during in the same lab. For example, the oxidation of cyclohexanol to cyclohexanone is expected to yield identical results for every student every year. However, the oxidation of 2, 3, and 4-methyl-1-cyclohexanol positional isomers can be done under identical conditions but will yield a more intriguing set of results. In this case, students can compare and contrast their results with their classmates a meaningful way. In fact, the Aldrich catalogue is filled with secondary alcohols that could be oxidized with minor changes in procedure. Almost every “traditional” experiment can be redesigned to investigate a cluster of related experiments. For example, the hydrodistillation of cloves yields an essential oil with a high proportion of eugenol. However, any spice can be hydrodistilled to yield many different essential oil combinations that can be analyzed by gas chromatography.

2) Include results from previous years’ experiments as part of this year’s data set. A year-to-year comparison of TLC R_f values gives a more meaningful data set than just looking at one student’s results in isolation or even this year’s class data. Data compilation can be spatial as well as temporal. This year’s class data can be compared with this year’s data generated at another institution.

3) Once data sets are created, stress statistical analysis as a way to interpret results. Larger data set indicate general trends and invite deeper analysis. Students can determine whether their results fit within a standard deviation of the class data. An expanded inquiry can be performed to determine whether the current class data fits within a standard deviation of the historical class data. Data analysis also gives insight into the reliability of the technique and/or the data gathering method. For example, students rating solubility of a compound in a given solvent as insoluble, somewhat soluble, soluble, or very soluble gives a wide range of answers.

Student Comments Spring 2009

This week I read through the student comments for the Spring 2009 semester. I have just finished posting them on the OChemOnline wiki. It was fun to read how the personality of the students came out in their comments. Some are self-depreciating – “don’t do the same stupid thing I did.” Others are analytical – “this is serious stuff.” Others are entertaining – “don’t stir your solution with your thermometer. It will blow up!” General observations: 1) Students are very time conscious. They don’t like to waste time. They like time-saving tips. 2) Students are very concerned about the mechanics of the experiment. In part, this was original thought that I wanted to elicit with the student comments project. Actually performing the experiment is different than reading about the experiment, writing about the experiment, or even teaching the experiment. These kinds of technical observations are the kind of things that comes through personal activities and careful observation. 3) There were a few “I wonder” type of comments but not many. This is definitely another level of the experimental process that is challenging to attain. However, I think we instructors should definitely strive to draw out these kinds of reflections. This is what most of use career chemists find interesting about chemistry. We can ask questions, and use the experimental process to find answers. And invariably along the way a lot more questions come up that are interesting to try and answer as well.

You Break It You Buy It

One of my summertime tasks is to purchase the consumables, equipment, and chemicals necessary for the next school year. We have not collected lab or breakage fees since I began working at Dominican. My impression is that it is common for schools to collect lab fees or at least require students to purchase glassware that they break. I think that the consensus at Dominican has been that after collecting $30,000 per student for their private college education it is adding insult to injury to ask for another $50 lab fee. Personally, I am happy that we do not collect breakage fees. Breakage fees encourage students to hide their mishaps. Students have a tendency to hide accidents even if they are not going to be charged for breakage. Collecting breakage fees also requires the instructor to be “the enforcer” and be the source of even more pain and agony for students than he or she already is. We have three or four lab sections sharing the same lab drawers so it would not be fair to charge students for glassware that is missing from their drawers at the end of the semester. On the other hand, students do break glassware that has to be replaced at a certain cost to the school. As far as lab fees go, lets face it, colleges spend much more for the education of a science major than any other student major. This is especially true for primarily undergraduate institutions that are getting very little, if any, grant funding. Should this added expense be reflected in how much science majors are charged for their education?

Gallate Diesters

The products from the acid catalyzed Fischer esterification of gallic acid with isopropanol (see “Fantastic Fischer” April 25, 2009) was chromatographed to purify isopropyl gallate. In addition to isopropyl gallate, another chromatographic peak was observed. This peak was collected and the NMR performed. Interestingly, this spectrum displayed three aromatic hydrogen signals at 7.207 (d), 7.153 (d) and 7.092 (s). Isopropyl gallate gives a singlet at 7.05 ppm. It also had four distinct septets at 5.130, 5.115 (overlapped), 4.692, and 4.562. Isopropyl gallate gives a septet at 5.129 ppm. The total integration for the aromatic hydrogens and the septets is about equal. I think what I am looking at is a mixture of two compounds created by the esterification of isopropyl gallate at the C3 and C4 hydroxy groups.