Two years ago, I saw a post here on ChemEd X about popping a balloon with an orange peel--and from this seed grew one of my favorite weeks of the school year.
I teach chemical bonding in a pretty traditional way (especially compared to the Modeling Instruction approach I use at the start of the school year), so while students are usually able to execute certain tasks -- drawing Lewis dot structures, for example -- the application of these tasks has been pretty limited, making it difficult for students to contextualize them, and especially for students with learning differences to do more than struggle to memorize a set of steps.
To address this issue, I’ve been working to make my curriculum more project-based, and to fold in more lab skills such as experimental design. While my chemical bonding unit is not a full-on PBL unit, starting last year, I have added in a final week of the unit that is a project-based application of the concept of polarity. It’s a nice way to generate buy-in, to revisit important concepts, and to practice (for the students and for me) some of the structures and skills of a traditional project-based learning unit: context first; NGSS skill-building; and student agency.
We start the unit watching the video of the balloon popping and do a QFT Task that you can find in the Supporting Information below (adapted from The Right Question Institute). Students have a LOT of questions about the video, and I ask them work in small groups to generate as many questions as they can, without judgment. It’s interesting to see which groups come up with the most questions -- it’s not always the kids I expect! Next, they categorize the questions and then pare those down into questions they are most interested in as a table. But I end up only collecting one “priority question” from each table. I write these up as a class list that we revisit towards the end of the week.
After watching the video, I remind students of the concept of polar and nonpolar bonds that they have learned previously, and ask them to apply this to the observations they make of the behavior of oil and water in terms of “how many drops fit on a penny?” Sometimes students have done this lab before, but I try to add new nuance to it by introducing the concept of intermolecular forces. For the next few days, students explore molecular polarity and intermolecular forces through simulations, diagrams, and even “traditional” worksheets. Students make posters modeling the interactions of polar and nonpolar substances, which I use to formatively assess their understanding, before we come back to the balloon pop scenario. By asking students to connect the more traditional instruction of content to the balloon pop scenario, I can build motivation as well as retention.
Rather than telling students what substance in the orange peel causes the pop, I task students with generating their own experiments. Students spend a day generating experimental plans using a template called the Balloon Lab Design Proposal (that you can find under Supporting Information below) in small groups; by completing the background section of the plan, students apply their knowledge of polarity to generate a molecularly-grounded hypothesis. This is also an opportunity for me to assess students' understanding of polarity.
In the last section of the mini-unit, students also use the limited materials list to come up with their own experiment. Students sometimes test the peels of different fruits; the juice versus the peel of a given fruit; extracted limonene versus extracted citric acid; balloon size; and more. Sometimes their experimental questions connect to polarity and sometimes they don’t; for my purposes, I don’t really care! This section of the mini-unit focuses on skills in experimental design -- generating appropriate variables and controls, procedure-writing, and more. I want all my students to have access to the experiment; regardless of how well they understand polarity, they can engage in the experimental process.
The whole first page of the experimental plan sheet, plus the procedure-writing, usually takes a class period. I collect students’ worksheets at the end and give feedback in the evening so that they can have more fleshed-out procedures. The next day, students receive their sheets back for updating, creating data tables, and writing rationales before they can get supplies. I warn neighboring classrooms that things might get a bit noisy -- students have a lot of fun popping balloons, and even those whose experiments don’t result in pops (such as those using lemon juice) usually get to use some limonene to get some balloon pop satisfaction. This is a nice lab to do on a Friday afternoon, as you might imagine!
The final stage of the sequence involves coming back to polarity. Students make and present posters showing their experimental plan, results, and explanation of those results in terms of polarity. This is an opportunity for students to review the key content (or learn it for the first time) in both generating the poster and hearing it from classmates during the share out. Audience members complete a feedback form (you can find the Balloon Polarity Lab Presentation form under Supporting Information). This template ensures that there is not a lot of redundancy in the presentations. I give a group grade for the posters but follow up with a traditional quiz to hold students individually accountable.
I like this mini-unit because it provides multiple access points for students to learn about polarity and to practice scientific skills, and is engaging enough that students still talk about it as a memorable unit even after they leave my class. It’s more than an “end of unit project”, because students are still learning and incorporating new content, but it doesn’t mean a complete overhaul of unit-planning during a busy time of the school year. I plan to replicate this structure in the fall, with units I can’t make project-based completely.