Reflection: Adjustments to Practice Leaf Chromatography - Section 6: Debrief


Sadly, I made one crucial mistake in administering this lab. My hope was that students would be able see the different compounds from the leaves nicely separated out on a chromatogram; after all, this is what happened when I conducted the lab. However, there was one thing I did not anticipate, namely that students would take longer to set up the lab than I had, and therefore they would not get the same results. The leaves in the alcohol do require a fair amount of time to soak before the compounds are dissolved in sufficient enough quantity that they will then be visible on the chromatogram. Next year I may shred the leaves in advance in order to buy some more time for creating the solution. 

When I was first starting as a teacher I defined a “failed lab” as a lab that did not produce the results that I wanted or expected. This is because I was new, and before the days of the NGSS. It was a time when I did not understand how important it is to let students analyze a procedure to fine-tune it. I did not understand how important it is for students to understand how challenging the scientific endeavor has been for humanity—all the false starts, all the failed experiments, all the wrong paths.

Now a lab that does not produce the results I expected is almost as useful as a lab that does. In this procedure most students did not know why I got a nice chromatogram while they did not, but in this video showing how to handle a "failed" lab I model one way to handle a lab that did not produce the expected results.

  Adjustments to Practice: The flawed notion of a "failed lab"
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Leaf Chromatography

Unit 1: Chemical and Physical Properties
Lesson 8 of 11

Objective: Students will be able to describe the purpose of and method for paper chromatography.

Big Idea: Mixtures can be separated into their constituent compounds using paper chromatography.

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  60 minutes
chromatography of chlorophyll
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