I use this introductory exercise at the beginning (the very first thing) of my one semester topics course in Bioinorganic Chemistry and as the first exercise in my Bioinorganic unit in my senior level Inorganic Course.  The exercise is a very simple one, but generates a lot of great discussion, requiring students to access knowledge from prior chemistry and biology courses, as well s common knowledge from sources external to their academic career.  Students are often surprised to see how much they know before a topic is covered.  

This is an in class exercise that I use to introduce structure and magnetism to a junior/senior level course on bioinorganic chemistry. The class is cross-listed between Chemistry and Biochemistry. All of the students have had general chemistry and organic (with some exposure to MO Theory). Many of the students have also had the sophomore-level inorganic course, which delves extensively into MO theory, and some of the the students have also had the senior-level course on transition metal chemistry which looks deeply at d-orbital splitting.

This is a simple in class exercise to review acid- base equilibria and to lead the students to thinking about metals as both Lewis and Bronsted- Lowry acids. I use it as a discussion starter when I introduce the role of metals in biological acid/base chemistry in my upper division inorganic course, but it can be used at any level once acid-base equilibria has been covered.