by Varsha Desai, Chemistry
Teaching Effectiveness Award Essay, 2018
Experiments in chemistry laboratories often have complex protocols where students perform several steps sequentially to obtain a “correct” product. Seemingly small mistakes can result in a domino effect that leads to inconclusive end results. For example, students forget to “mix” a solution after dilution, and hence all their downstream steps are erroneous. Or they do not separate the aqueous and oil mixture enough while purifying biodiesel, resulting in impure oil-water emulsion rather than pure biodiesel. I realized that a common source for such mistakes is a lack of understanding of the protocol. More often than not, students either passively follow the lab manual, and thus occasionally miss steps, or spend too long doing steps where precision is not actually critical. To ensure a more active learning environment in the laboratory, I took a three-step “what, why, how” approach, such that the students ask themselves “what am I doing?,” “why am I doing this?,” and “how can I explain my results?”
First, to ensure that the students know “what” they are doing, I had them write a summary of the procedure as part of their pre-lab for 2 out of 16 points of their lab report. While grading these, I noticed that there were three groups of students: 1) students who copied the protocol from the lab manual word-for-word; 2) students who wrote just enough to show they put in effort; and 3) students who wrote a well-summarized, concise procedure. Most of my students fell into the first two groups by writing either too much or too little. In order to actively help them write better protocols, I thoroughly graded their pre-lab procedures for accuracy rather than completion. Specifically, I crossed out redundant information and noted important information that was missing. To further facilitate learning, I gave them a grace period of three labs where I graded the protocols based on completion but provided extensive comments as feedback. With every iteration, I saw a dramatic improvement in the students’ ability to write concise but detailed protocols. This resulted in a decrease in trivial errors, such as forgetting to add compounds, and also increased their speed in doing the experiments such that we always had time to discuss their results. Furthermore, there was a significant increase in class participation during pre-lab lecture, as students were more familiar with the procedure.
Second, students must understand “why” they are performing the specific steps in a protocol—this helps them discriminate between the parts of the protocol that are critical and parts where there is room for error. During my pre-lab lecture I drew a flow chart of the procedure and then discussed the reason for performing each step, focusing mainly on conveying important concepts. During this discussion, I also encouraged students to highlight the critical parts of each protocol and we collectively marked them on the board using a red marker. In the Chem 1AL laboratory, the extraction of biodiesel from the synthesis mixture is one of the most complex protocols that the students have to execute. In order to obtain pure biodiesel, students perform salt washes and then dry the biodiesel with magnesium sulfate. During the salt washes, students must be patient and pace themselves to allow for full separation of the aqueous and oil layers prior to proceeding with the drying step. On the other hand, students can be less meticulous during drying as long as they add an excess of magnesium sulfate (drying agent). By explaining why certain steps require precision while others don’t, I was able to convince my students to slow down and perform the important steps more carefully. This thorough pre-lab protocol and pre-lab discussion resulted in 29 out of 30 groups obtaining pure biodiesel.
Lastly, when students got undesired results, I asked them “how” their results can be explained and encouraged them to think of potential sources of error. During the biodiesel extraction, the group that did not get pure biodiesel said their potential error was that they vigorously shook the tube during salt washes rather than gently tumbling it, resulting in oil-water emulsions that were difficult to separate. Such answers clearly demonstrate that students critically thought through the procedure and understood where the errors could have arisen rather than writing clichéd answers like “my experiments did not work due to human error.” By establishing this “what, why, how” approach early in the class, the students got into a habit of actively interpreting the protocols rather than just passively following them. In fact, on several occasions students also altered the protocols to correct for their mistakes. One of the most striking examples occurred during our titrations of weak bases: if students passed their equivalence point, they realized that by adding a known amount of the weak base to their solution, they could go back to a point prior to equivalence and resume the titration. Overall, this approach required a sustained effort from both the students and the GSI, but led to a much richer learning process.