The CEC Game.

Clay mineralogy, cation-exchange capacity, and acquisition of nutrients by plants are challenging concepts for students to grasp. A CEC ‘board’ game was developed to demonstrate two important principles governing CEC and how a plant root acquires nutrients. This game also reinforces the four major silicate clay minerals, location of charge imbalances created by isomorphous substitution and pH-dependent charges. It provides visual clues to illustrate which of these clay minerals has the highest CEC and why. Two prototypes have been developed and tested in multiple lab sections of an introductory soil science course: a magnetic version and a felt board version. Students receive a brief lecture to reinforce concepts previously discussed in the lecture portion on the building blocks of clay minerals, sources and location of charge imbalances, principles governing CEC, and shrink-swell properties. Students are provided a felt board that have the four major silicate clays illustrated as either 1:1 or 2:1 type clays with relative distance between silicate sheets, a die, and felt or magnetic pieces that serve as cations. The goal is to exchange hydrogen ions for cations on exchange sites while following the principles of charge equivalency and cation selectivity. After a set time, students add up their charges (not number of cations) and subtract for any aluminum acquired during play. The player with the most charges wins. Student feedback was positive and (anecdotally) students scored more points on exam questions related to this topic compared to previous years prior to the game development.