An experiment with how I teach limiting reagent

I know that I haven’t posted in a long time. My fall has been a lot busier than I was ready for, so I’m a bit behind. But, last week something really cool happened.

If you’ve read my blog at all, you know that I am a bit of a traditionalist (not saying that’s a good thing, just the reality). For my DP Chemistry classes, I tend to use a lot of lecture and practice. I’ve found that for my DP classes where I have a prescribed set of content, it’s the most efficient way of getting through a large amount of material. But as I’ve admitted, I want to become a better teacher and challenge myself to be more creative in how I teach. I want my students to get more out of class than a good grade on their IB exams. I still have a long way to go on this journey.

But I think I made a small baby-step last Friday.

Instead of teaching the topic of limiting reagent in the way I’ve taught it the previous 17 years, I tried something completely new. I gave my students a few small and simple examples. The first example uses sandwiches. It’s a common analogy that’s used for limiting reagent. If I have 20 slices of bread, 14 slices of cheese, and 36 slices of turkey how many sandwiches can I make? (Assuminng sandwiches in this case are 2 slices of break, 3 slices of turkey and 1 slice of cheese.) This allowed me to get across the basic concept of limiting reagent, as I know all of my students can relate to sandwiches.

Then I gave them a chemistry example using moles. If 2 moles of nitrogen react with 5 moles of hydrogen, how many moles of ammonia will be produced? (In the process, determine the limiting reagent and how much of the excess reagent will be left over.)

We talked through the example, with students sharing their ideas for how to solve it.

Then…instead of simply continuing the lecture and showing them the ‘real’ example with grams, I asked them to take the real example and develop their own method of solving the problem. I gave the process to the students. Then I wandered around and asking leading questions. I was amazed at a few of the methods that students developed. One student used gram ratios instead of mole ratios. He did this while taking the balanced equation into consideration, so it was valid. I NEVER would have thought of using gram ratios. I was incredibly excited that this student figured this out. And I know this student was also incredibly excited to have thought through his own method. I don’t think he’ll forget it.

And as a fall-back, I recorded a lecture with my traditional method of teaching. This will allow students that weren’t able to develop their own method, or who didn’t have as much confidence in their method, to look at my method and see if it makes sense. So the beauty of using the flipped class model here was that I flipped the class from me telling them how to solve a problem to challenging them to develop their own method.

Today, I taught my Standard Level class the same lesson. I was a bit worried since I had a shorter class. But almost all of the students left with a decent understanding of their method. One student worked through frustration, almost ready to give up. She kept working at it, and finally got it!

I’m still not perfect, but it was fun to try something new and feel as though it was successful. I’m giving them a quiz on Friday. I can’t wait to see the results.


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