The unspoken word of chemistry: Non-stoichiometric. Stoichiometry and non-stoichiometry are concepts that combine to make a solution that does not have to be difficult to understand.
The lab activity shared here is a simple experiment where students use stoichiometric principles to experimentally determine the amount of sodium bicarbonate in an Alka-Seltzer tablet. Novice students tend to find stoichiometric calculations difficult, so practicing the calculations on a pre-lab assignment boosts their confidence and ultimately leads to more successful labs. The Asynchronous Video Pre-Lab Assignment shared here demonstrates the procedure and the calculations required in the experiment.
In this virtual activity, a video introduces stoichiometry and guides students to think conceptually using a simple baking analogy. Afterward, stoichiometry calculations connect to the analogy, that are then reinforced with a simple experiment. Finally, students explore a PhET simulation to deepen their knowledge.
The first unit in my sequence for AP Chemistry covers stoichiometry and reactions. The new AP Chemistry Course and Exam Description has identified Learning Objectives which need to be taught and practiced to ensure students perform well on the AP Chemistry Exam. I will identify and describe activities I use to teach students some of the Learning Objectives that I tie into this unit.
This lab is one of my favorite activities to do in my classes and I look forward to it every year. The lab is simple, requires limited supplies, students love it (i.e. high engagement level), and I have found it to really set students up for stoichiometry.
If you want to lose weight, you have to burn calories. Anyone who has gone on a diet knows this. But when someone loses weight, have you ever wondered where the lost mass goes?
Recently, my district made a commitment to helping its teachers reflect and rethink their grading and assessment practices. One of the phrases I kept hearing throughout our staff professional development sessions was authentic assessment. I understood (and agreed with) the basic premise—create more opportunities for students to perform tasks that demonstrate meaningful application of essential knowledge and skills. Doing so involves going beyond, or even potentially replacing, traditional summative assessments at the end of each unit.
A solid grasp of proportional thinking is crucial to being able to solve all sorts of problems in chemistry as well as “real life” situations. While many students seem to intuitively understand that one mole is equal to 6.022 x 1023 particles when the analogy is drawn to a dozen eggs, for some, this sort of equality is a puzzling mystery.
A discussion of how students solve stoichiometry problems.
In my class, I use the illustration of a mountain to help students push through the challenges of chemistry. Stoichiometry is the top of chemistry mountain. As we progress through the year, I say things like “the mountain is getting steep here!” or “there is not a lot of oxygen up here!” or “I will carry you up chemistry mountain if I have to!” to keep students motivated. When students finally get to the top of chemistry mountain (mid quarter 3), the air is thin, they are tired and they are ready to base jump off the mountain (see illustration from a former student below).