Doing the Candium Lab Differently

When I began teaching high school chemistry I inherited many wonderful resources.  One notable one was the popular Candium Lab.  A search of the Internet will produce a multitude of versions of this activity which addresses average atomic mass.  Virtually all of them, like the one I discovered, are cookbook labs.  The average atomic mass is described, an algorithm is provided for determining the average mass of a sample of a mixture of three candies.  Most also provide the data tables and additional practice problems.

When I first used the lab my students found it very confusing.  I was answering questions for each lab group all through it.  I first wrote it off as my fault.  I hadn't done it before and so I hadn't properly prepared them to do the lab.  Then I thought about the type of questions they were asking.  They didn't seem to know why they were being directed to do what the lab handout said to do.  They were just going through the motions.  The intent of this lab is to model the process by which we determine the average atomic mass of each element based upon the relative mass and abundance of each its isotopes.  I didn't think that the students were seeing it as a model.  They thought of the lab activity as just one more set of instructions to follow which happened to end with eating candy.

I wanted them to be conscious of the analogy and to think through the process required for themselves.  Since one of my goals is to get my students to practice the skills of scientists I begin the course by teaching them to not only make their own data tables during experimentation but to design procedures.  I decided to makeover the Candium Lab as a challenge.  After direct instruction and guided practice in determining average atomic mass I presented the lab activity as independent practice.  I did not print out a lab guide or fill-in sheet.  I merely dumped the three types of candy into a large clear bowl and mixed it up.  I told the students that I wanted them to determine the average [atomic] mass of a fictitious element "candium."  The bowl represented the candium found in all of nature, their dixie cup portion a sampling of it.  I asked that each lab group come up with a procedure for doings so and then to call me over to hear, refine with them if necessary, and approve their procedure.

The fallout was clear.  The students were aware of the model.  They applied the procedural knowledge from the lecture and practice to a new novel situation.  Additional positive results included a sense of satisfaction in rising to a challenge and confidence building in using basic mathematical skills to solve a science problem.  A lesson learned was that students do not need to have everything completely scaffolded for them and indeed should not if we want them to joyfully truly learn.

Another alternative modification would be to place the candium activity at the beginning of Bruner's Discovery-Introduction-Application Model.  Here one would treat the candy merely as candy and ask for the average mass of a piece of candy given that there are three types of candy present in a variety of abundances.  Then one would reveal the analogy and give practice with another application of the procedural skill set involved.