Think back on your own high school experiences in science and math classes and you may recall completing a series of out of context practice problems. While practicing the methods we use to calculate quantities such as cross multiplying, dividing by a common denominator, or finding percentages has a place in education, the method of providing endless practice problems isn’t always the best way to introduce the calculation. In first year chemistry classes we often introduce simple mole calculations, converting mass to moles and moles to mass. In the past, after introducing Avogadro’s number and the importance of moles, I had given tons of examples to help students convert moles and mass without context. While I still provide that practice, it now comes after the activity that I have attached below.
In this activity, students are asked to identify ingredients in common household products such as pretzels, Redbull, and aluminum cans. The students are given one quantity such as the mass of salt contained in the pretzels or the moles required to create the opener of a soda can. Students are asked to calculate other quantities including the mass, moles, and number of particles contained in the sample. After completing the calculation, the students need to measure the quantity described and bring it to the instructor. The instructor should have their own balance and check how accurate the measurement is. If the students solve and mass the correct quantity on the first attempt, they score 10 out of 10 points. If not, the instructor can provide a small hint and the students can attempt the calculation and mass again resulting in a score of 8 out of 10. If the students still fail to produce the desired quantity, the instructor can provide more detailed instruction and the students will earn a 6 out of 10. I have found that my students really had fun with this “challenge activity,” as we called it, because they felt competitive to achieve the highest score and could see how the measurements and calculations worked together in lab.
I think this activity is helpful in various ways. The students practice the same calculations we would have in our drab, boring handout, but now with real world examples. The students can start to visualize the size of these quantities and when they come to have their accuracy checked I often say things like, “Can you BELIEVE there are 1.20x1024 particles in there?!?” to highlight the small size of the particles themselves. Especially when it comes to the amount of sugar in half of the Redbull can, students are shocked. The colored cups and containers I use in the lab activity were just a quick way for me to see what I will be checking as they approach my desk. For example, as soon as I see a blue cup I know I am looking for my salt numbers and when I see a red cup I know I am checking my sugar values. The measurement aspect of the lab is just reinforcement for measuring values and taring scales but also reminds students that the only way to know how many particles is in a substances is to mass it on the balance and then perform the calculation. Later in the stoichiometry unit, when students start to forget why we need the mole I like to recall this lab and how essential it was to use the mole to transform numbers from mass to particles.
I would love to hear more ideas to add to the activity, or any modifications you may have made. Reach out on ChemEd X and share your thoughts. Additionally, consider heading over to Twitter where a lot of ChedEd X contributors and other chemistry teachers are sharing ideas such as these with the hashtag #iteachchem.