Teaching Percent Composition, Empirical and Molecular Formulas through the Lens of Aspirin

round shape with capital letters spelling ASPIRIN within a notebook

As chemistry teachers, we often think about how we can make our subject “real world” for our students. We want them to be able to connect concepts to their lives, as we know that this increases not only their interest in the course, but also engages their prior knowledge and increases their long term retention of the concepts. Along with that, we need to connect related topics for our students. What may seem obviously linked for us as experts may not be quite so obvious to our first-time chemistry learners.

I am currently teaching chemical quantities – our first unit after the winter break. One of my favorite real-world applications that I developed is in this unit. A few years ago, when I was designing my lesson for percent composition, empirical formulas and molecular formulas, I was pondering the fact that my students struggle to connect these three topics. They are inherently related, so why don’t students see the link? I decided that it was because of the way we chunked the topics – we treated them as three separate lessons in class; therefore, students didn’t link them even though we assigned integrated problems after they had independent mastery of each individual topic. The challenge was how to teach each of these three problems so that students could identify and know how to solve each type of problem while also seeing how they related to each other. The most obvious way to make them connect for students is to teach them in a physically-binded format – I chose a flipbook. I then began working on linking them even more by having all of the teacher-modeled examples center around a central theme. A real-world, very familiar, easy to understand theme that didn’t get too muddy mathematically was that of aspirin. I designed a flipbook that looked like an aspirin tablet, and imbedded notes and aspirin-related questions within its 4 pages.

percent composition
Procedure time: 
30 minutes
Prep time: 
10 minutes
Time required: 

It should take about 30 minutes for students to complete this flipbook activity. I tend to break up the time over two or three days. 


Aspirin foldable copies, scissors, stapler, glue or tape (if adding to an interactive notebook)


The flipbook can be printed on two sheets of paper and stapled down the side. This does require some cut and staple time by the students. I try to pre-cut the half pages, and then have the students stack the pages and cut out the ovals. I give them a time limit, and increase the impact of the real-world application, by showing the TED-Ed How Aspirin Was Discovered while they assemble the flipbook. The back side is left blank so that it can be glued into an interactive notebook if desired. (While I will be sharing so much more over the next calendar year about interactive notebooking, if you are interested in learning more now you can watch a webinar I did for AACT in February of 2020 entitled Teaching Chemistry in a Textbookless Classroom. This aspirin flipbook was shared as an ancillary material there as well.)

Figure 1: Aspirin activity in our interactive notebook

How the flipbook is filled-in is flexible. While I want students to connect the concepts, I do still teach them one at a time, and ensure that they can solve each type of problem before moving on to the next. I usually take a few minutes to fill in the notes section as a whole-class. After introducing the process on the right-side of each page, I have the students work with their desk partners to see if they can fill in the left side examples; sometimes on whiteboards first. We then work through the examples as a class, and students correct their work and copy the examples in their flipbook. We then go through other examples, either from a traditional worksheet, task cards, or using ChemQuiz.Net.

It’s amazing to me how this subtle change has made a difference in the way my students view these topics. Some things are the same:

  • I still take a standard period to teach each skill.
  • We still practice problems where the skills are isolated initially.

What has changed:

  • In flowing from one topic to the next, students see that they are related and it feels “easier” to them.
  • When I present integrated practice problems, the students don’t seem as thrown.

Figure 2: CSI Case Profile in our interactive notebook

Finally, but perhaps most exciting, my students have an understanding of how a common compound applies to their everyday lives. At the end of this mini-unit, I integrate all three topics by having students do an Empirical and Molecular Formulas CSI activity. Many versions of this can be found with a quick search online and I cannot find the original author. I set up a crime scene in the room, and students solve the mystery by performing calculations from “CSI data” and then solve the murder mystery. This provides a final tie-in to the aspirin theme. You can see what that piece looks like in our interactive notebook in figure 2. 

By taking a traditional lesson and giving it a theme, new interest in content can be fostered. I hope this inspires you to think about other ways we can make chemistry real for our students. My experience with this activity has taught me that it doesn’t require as much time to change things up as it sometimes seems like it might.


I try to pre-cut the half pages but you can do more or less of the preparation depending upon how much time you have.


Teaching Chemistry in a Textbookless Classroom, AACT Webinar recording, February 19, 2020. Membership required. https://teachchemistry.org/professional-development/webinars/teaching-ch...

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Comments 3

Leonard Freidhof | Fri, 02/04/2022 - 09:42

Anyway we could get this as a pdf.  I don't use microsoft word and open office won't open this correctly.  Thanks.

Deanna Cullen's picture
Deanna Cullen | Fri, 02/04/2022 - 14:45

Thanks for your interest! I just added pdf versions of both the student and teacher documents!