High School chemistry students are taught about ions, salts, water, and solution formation. In their biology classes they are taught about proteins and their functions. It turns out that ions impact the folding of proteins in an ion-specific way based on how well an ion interacts with water. For example, sulfate or even fluoride are well hydrated and promote protein folding; however, iodide is poorly hydrated and causes unfolding and denaturation. In 1888 Franz Hofmeister first documented the observation that the identity of the ion matters in this way. This Hofmeister series has, since, been shown to manifest for numerous processes that take place in water. As such, it appears that ion-specific effects are actually rather general. The Hofmeister effect, as it is now known, can easily be demonstrated to high school students using cheap and readily available materials such as egg whites, salts (NaCl and NaI), and distilled water.
Here we provide a detailed lesson plan for teaching 10th graders about Hofmeister chemistry and intermolecular forces. We also provide a set of worksheets for the students’ curriculum. For the convenience of modification, Word files of lesson plan and worksheets can be downloaded here. Specifically, we focus on interactions between ions, water, and proteins. The lab can reasonably be conducted over the course of two or three 45-minute classroom sessions. In brief, mixtures of egg whites + water, or egg whites + a salt solution, are heated until the protein unfolds and denature causing the solution to turn cloudy. The temperature at which this occurs (called the cloud point) is impacted by salt, and differently by iodide versus chloride. We also provide a youtube video where to demonstrate and discuss the experiment and concepts. This entire lesson plan and lab can be tailored to a teacher’s specific classroom.