Experimenting with Stoichiometry

I loved my high school chemistry teacher. That’s an important place to begin. I was mesmerized by every lesson, every concept. Chemistry seemed like magic. But not phony don’t-look-too-close magic. Real actual magic. The ideas captivated me, but the math slowed me down. My teacher often posed a problem, gave us time to work on it, and then logic-ed his way to the answer. He talked about mathematical relationships with a fluency that I didn’t develop into well into college and I found myself floundering, often, as I tried to apply what I learned.

When I student taught, my cooperating teacher had a very discrete way everything would be done. I stood in front of the class, but he had very much scripted what I was supposed to say. So it was with teaching stoichiometry, the mathematical relationships between substances in a chemical equation. He required me to teach it in a specific way, using the dimensional analysis or factor-label system of canceling units. The way I am describing this, it sounds like I felt bound or bullied, but it was quite the opposite. When he showed me what he wanted me to do, I had an a-ha moment. It was so easy and made so much sense. I wished I could go back to high school chemistry and do it all again with this tool. For my entire 25-year career I have taught stoichiometry as my cooperating teacher showed me because when he showed me, it helped.

Fast forward to this past December and my 25th pass at stoichiometry. I don’t know what happened. I had been to a couple of math in-services where teachers are doing less direct instruction, more collaborative group work and more “let students figure it out.” For years, my colleagues in a ChemEd google group have argued whether the method I use is a savior or a crutch. I didn’t start with my typical stoichiometry lessons; I let students figure it out.

There were bumps in the road. After two days of practice and a lab, we took a quiz. The results were not quite what I wanted, so I offered a re-take. Not that many students took me up on it, but, after they had, my average was just about where it is every other year. Those quizzes were more difficult to grade. When you only give students one way to solve a problem, they are easy to grade. By quiz day, I had helped them with at least three different ways – that really are just variations of the same way – and all three were being used. Reviewing the homework was also more challenging. When a student asked for me to work one out on the board, I had to ask what method they wanted me to use. Even as I type this, I realize that I should have had them work them out on the board instead. I don’t do enough of that.

When we returned in January, we revisited stoichiometry because we hadn’t tackled the concept of limiting reactants (when one ingredient runs out, the product can no longer be produced – think “dead battery”). I considered “hitting the reset button.” Maybe the winter vacation amnesia would erase all those methods and I could re-teach the concept in my old-fashioned way and put my train back on the comfort tracks. That, though, would defeat the purpose of what I did in December, so I stayed the course.

We started the semester with some conceptual treatments of limiting reactants. We did an experiment where balloons were inflated to different levels and used model kits to build molecules until we ran out of something. On limiting reactant math day, I sorted the students by how they had done on the quiz I mentioned above. I provided some videos of the problems they would face and gave them the option of watching the video, going at it without the video, or combining the two as they needed. I moved around the room and gave help as they asked for it.

Again, bumps in the road. Students who had scored lowest on the quiz often neglected their homework. They chose not practice what they had learned – or struggled to learn – in class. This is my greatest worry: What if trying this “figure it out” is detrimental to the students who need the most assistance? It’s also an interesting aside: Do students often not do their homework because they know they may not get it right? The quiz scores were even lower than the previous quiz, 2 or 3 points lower than my typical average. Thinking back to my own high school chemistry experience, when I didn’t understand the math, I assumed the breakdown was mine. The tide in education has turned now and it feels to me like struggling students blame the teacher first, or at least that’s what they verbalize. Plus, some don’t seem to believe that if they try and try and try, they will eventually get it. And that not mastering everything right away isn’t a death sentence.

In two weeks I will return again to stoichiometry in the context of the gas laws. I am hoping that with each new treatment of this concept, I pick up a couple more strugglers along the way. But I have to find a way to hook them back in, to get them practicing again, to help students who were like me experience the success I felt when I student-taught. Do you have any ideas to help? I am all ears.

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