Submitted by Michelle Personick / Wesleyan University on Wed, 06/23/2021 - 12:38
My Notes

This is an in-class activity that I use in my advanced general chemistry course to teach students how to rank the relative acidity of monoatomic cations and how to qualitatively predict the strength of the interaction of these cations with water (hydration and hydrolysis).

I teach the students that these properties trend with Z2/r (where Z is charge and r is radius). They are generally comfortable calculating Z2/r and comparing the result to a table in their textbook to assign relative acidity, but struggle to make this assignment qualitatively without looking at the textbook. Being able to qualitatively make these assignments helps students when we get to predicting solubility of compounds using Bronsted acidity and basicity. In the course as a whole, I emphasize the power and importance of being able to qualitatively predict trends in reactivity, in part to provide an alternative approach to the fall semester of the course--which focuses on quantitative aspects of physical chemistry--and in part to prepare students for organic chemistry, where they can't simply plug a product into an equation and generate a synthesis.

Learning Goals

Students should be able to rank the relative acidity of different monoatomic cations.


Equipment needs


Implementation Notes

I have the students work on the activity in groups and then we discuss it together at the end of class. When I used the activity I was teaching via Zoom, so I had students collaborate with their group in a Google Doc (one page per group) and I followed along while they were in their breakout rooms. I taught my class in a flipped format, so the activity is designed to take a full 50 minute class period, including introduction, group work, and full class discussion.

The "Wulfsberg textbook" that is referred to is Gary Wulfsberg's Principles of Descriptive Inorganic Chemistry (University Press). The same table appears in all of the Wulfsberg inorganic textbooks. The students only need a single table, which could be provided by the instructor as a handout.

Time Required
40-50 minutes
Creative Commons License
Attribution, Non-Commercial, Share Alike CC BY-NC-SA