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Splitting the Difference: Predicting Reaction Products - Education Impression

Splitting the Difference: Predicting Reaction Products


Tonight I started watching this video of a keynote address by Dan Meyer and friends from the California Math Council Conference. Dan describes teachers as being lucky because we get to consider interesting questions every day in our work. The first friend to share some questions is Shira Helft and she has me thinking about some of my questions. Lately, I have been thinking a lot about differentiation. How can I differentiate in a way that lets my students who are ready work on enriching content while providing extra practice for students who need that? I’ve been working on that in my current unit; it has been a good question to tackle this month.

By December, my students and I have finally made it to chemical reactions, the heart of chemistry, the fun stuff. I love this unit because every day leads naturally to the next, every day builds on a skill that came before it. Simultaneously, it’s also the end of the semester and gaps in understanding have developed for some students; my awareness of those sharpens. This week I have been teaching students to predict the products of chemical reactions, a topic that traditionally slows many students down because it relies on so many skills they have learned so far. If students don’t draw on all their chemistry knowledge, and this is especially challenging where gaps have developed, they struggle. 

To combat this, I started by giving the class 5 reaction beginnings and asked them to guess, individually and then with their groups, the products. In every class the results were the same: students were able to correctly guess at the outcomes but stumbled a bit with the actual chemical formulas. Then I introduced the activity series and solubility table as tools that allow us to predict whether a reaction will occur at all. I would have liked one more day for this to really develop the idea that sometimes a reaction doesn’t occur, but the semester timeline did not leave me that as an option. After this first day, students completed a homework assignment where they had to predict the products of 7 reactions.

When they came to class the next day, I used our LMS to collect their homework answers. In about 5 minutes, I could see how many questions each student had correctly answered. Now to differentiate. I split my class in half and both halves completed a different experiment. For students who struggled with the homework, there was a predicting products experiment. Students explored six reactions – a synthesis reaction, a decomposition reaction, and two single and double displacement reactions – for signs of reacting. They would need to predict the products for each reaction that actually took place, providing them with the visual of what it looks like when a reaction does and does not take place and a second opportunity to apply the skills from the day before. For the half of the class that mastered the homework, a puzzle awaited. Given five solutions (AgNO3, BaCl2, CuCl2, K2CO3, and NaOH) in numbered droppers, could they discover which solution was in which dropper?

What I liked: It was easier than I would have guessed to run two different experiments simultaneously. I split my distribution table down the center and placed the chemicals for each experiment on one side or the other. The students managed that process easily. 

Students who needed more practice got it and students who were ready for something more got that too. Without two options, one of the groups would have missed out on what they needed.

I love this inquiry lab of discovering which solution is which. The thinking students do on this day, and the collaborating and knowledge checking, is rich. And fun to watch. The reactions in the other lab are also interesting; it never gets old watching a split relight when inserted into a tube of decomposing hydrogen peroxide. Good reactions (heh heh) by students to both experiments.

On the quiz that followed this differentiated lab day, the students achieved good results. The average grade was about a 90%, better than I have typically seen in other years. Only about 10% of my students scored below an 80%. It felt like a big win to see students who had only correctly answered half of the homework questions to ace the quiz.

What I think could be better: With a little more time, I could have done a better job at making sure students had predicted reaction products before each stage of both experiments. Instead, some are “predicting” after the experiments are complete so they can interpret results. That’s far from ideal.

One of these experiments – identifying the five solutions – is a rich and engaging task. The other – predicting the products cookbook-style – provides good practice with engaging experiments, but isn’t as cognitively challenging. I hate to remove this opportunity for great thinking from some of my students. On the other hand, without solid knowledge of how to predict products, would they have the foundation to really dig in to the problem? And, there I am, back at the initial question.

What are you doing to tackle questions like these? What are your answers? I’d love to hear more about them. Please comment.

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