Saturday, February 6, 2016

Teach my [Stoichiometry] Lesson

A few weeks ago I wrote about a new approach I tried to teaching stoichiometry, the fundamental math of chemistry. At almost the same time, I wrote a post in response to a blogging initiative launched by the MathTwitterBlogoSphere (#MTBoS). This post is a follow-up to both of those things. This week the #MTBoS asks us to post about a lesson we taught this week. What went well? What didn't? 

The Lesson

This week I taught a lesson that is part of a progression of stoichiometry lessons. In the past, I might have stood at the board and prodded my students with questions to help them lead me to the answer using a problem solving strategy that we have practiced all year. In the past couple of years, I made a presentation available to all students and they could use it (or not) to assist them as they worked through the problems while I circulated to help and answer questions. I wanted to try something slightly more differentiated and targeted this year, partly because my experiment in the stoichiometry lessons of a few weeks ago left some students really struggling.

I looked at scores from two quizzes and put my students into three groups. The smallest group was 5 or 6 students from each class whose quiz scores revealed deficits in this content. These students received small group instruction with me during my lesson. The students who did fine on the two quizzes completed the math problems with the presentation. All these students solved the same 6 problems, but some did them with my modeling and elaborations and others checked their work against a digital version of the notes. I predicted that the students who aced both quizzes were ready for more of a challenge and didn't need either my instruction or the technology assistance. I wrote a difficult problem and told them to try to solve it. Once I had the small group working on something, I could still circulate and answer questions in the two other groups. After the extension group finished solving the problem, I made the chemicals from the problem available so that they could carry out the reaction from their problem. They created a balloon full of hydrogen gas that they ignited!

Anecdotal Benefits

I saw benefits to this version of my lesson while teaching it. The group working on the extension had excellent conversations in all classes where they worked together to solve this problem, asking and answering great questions. They all arrived at the answer with minimal assistance from me; eavesdropping on their awesome conversation was spectacular! When I told them that they would carry out the experiment and light the balloon, they loved the idea of that. Still, I wasn't prepared for how much they would enjoy doing it. One student who has said very little to me all year, looked at me and said, "This is the greatest thing I have ever done."

The experiment opened up an opportunity for more great conversation. They had calculated the size of the hydrogen balloon, but the balloon did not inflate nearly as big as their [correct] calculations predicted. Why is that? They had very interesting ideas about this and it was fun to share them.

As sexy as an exploding hydrogen balloon is, my favorite benefit came in the small group setting. One student who has had a very difficult year almost always sits with students who are outpacing her in class. In the small group setting, the person next to her did not understand how to set up a problem, so she showed him. Without differentiating like this, she would not have had the chance to demonstrate her knowledge and he would not have been able to thank her for doing so, but both of those things happened during the class. How nice it must have been to go from being the person who asks for help to being the person who provides it!

The Data Don't Lie

The lesson was really fun to teach, but if it were just fun without content gains, it wouldn't have been worth it. At the end of the week the students took a quiz over the concept. I was anxious to see the scores to see if this approach had helped or (please, no!) hurt. The average score on the quiz was a 13 out of 15, right around my typical average for a quiz and just a shade higher than last year's average. Fourteen students in three classes had received small group instruction. Eleven of those students improved when comparing this quiz score to the previous two that were used to group the students. Four of those students had failed at least one of the previous quizzes and passed this one, some by earning As or Bs this time.

The Takeaway

In my classroom, I struggle to differentiate in a way that is not too hard to manage and doesn't make anyone feel badly for whatever version of the lesson they complete. I also try to keep things open-ended and challenging, but I think I do model more often than I need to, especially for students who are ready to go it along. This lesson was a step in the right direction in both of those areas, so I am going to look for ways to expand this in coming units.


  1. I'm a math teacher who is asked to teach Chemistry (& Physics) at my small school, so I was really excited to see your blog post on Stoichiometry, which we're tackling now, too!

    I had an interesting interaction this past week when my principal observed me "teaching" stoichiometry (it was actually day 2 of stoichiometry where students would work on a problems on whiteboards and switch partners when I gave the signal). Both my principal and I were Chemistry minors in college, so we knew our stuff, but neither of us were trained to teach science (he, like me, is a math teacher).

    He was taught using dimensional analysis/factor-label system, as you referenced in your other blog post, but I was taught to label grams and moles on every compound in the reaction, so it was interesting seeing students try to understand his way of explaining it. He suggested that I try teaching it his way in one of my two classes, thought that would be for next year.

    The exploding hydrogen balloon sounds awesome! What a cool extension for students who "get it". My only question/worry is, as you pointed out, would students who are in the small group with you start to feel worse and "stupid" because they recognize that they're always in the slower "we didn't get it yet" group? I've been doing random grouping for that reason, both in math and in science, and I've really liked how it's going. However, it does miss out on those interactions, like you said with the girl who became the "helper rather than the helped", unless they were randomly assigned together (which likely wouldn't happen? I dunno.)

    I'm also interested in how you "let them figure it out" from your other blog post. In math I'm getting better at that sort of thing, but in Chemistry I still lean too heavily on lecture 99% of the time. Have you ever heard of the Modeling curriculum? That might be just want you're thinking of. I do it in Physics and it's incredible, but I've never tried it Chemistry, mostly cause I think I'm too intimidated that it won't work as well. That and I haven't attended a summer class on it and want to do that before I try it. Here's their website:

    They have some sample units available, but unfortunately you have to become a member (only $30, I think) to get access to all the units. I don't know why I haven't done it yet.

    Good luck and thank you for sharing! One of these days I'll have to do a blog post on how I was taught (and now teach) stoichiometry!

  2. Thanks for commenting and sharing the modeling website. I'd love to read more about your approach to stoichiometry!

  3. I have used a flipped classroom approach to stoichiometry for the past few years that includes some of the elements of your differentiation--students who need extra help after watching the online lessons form a group that gets extra help they need, the other students work with each other, and there are always challenge problems. I like the idea of allowing those who complete the challenge question the ability to perform their reaction and I'm curious about what the reaction was and why their reaction did not produce their expected theoretical yield. Did you "sabotage" their reactants and give them an impure reactant or did you make one reactant (unbeknownst to them) limiting? Had you covered limiting reactants yet or was this a first introduction to the concept?

    Thanks for your great blog!

    1. The reaction was just zinc and hydrochloride acid. The kids had a lot of interesting ideas about what prevented the balloon from getting to its full size - loss of reactants (zinc lost when filling the balloon) or gas escaping between test tube and balloon or not enough pressure to force the hydrogen into the balloon. Lots of good thinking!

  4. Nice. Congratulations on successful differentiation. You made it look easy. I would love for you to dissect that portion more sometime.