TEACHING REDOX AS A CHINESE BUFFET

Redox is difficult for many students to understand if they lack substantial training in chemistry; a commonly used textbook figure looks like a spaghetti diagram. I explain it with an analogy to a Chinese buffet, which I am visiting near the end of the day. All entrees are available, but when the trays are empty, the food will not be replenished. The concentration of organic substrate being oxidized (electron donor) that decreases with time in the diagram represents my stomach space. As I eat and electrons are taken up by chemical reactions, that space gets smaller and smaller. How I fill it is important. I do not eat rice or eggrolls; I go straight to my favorite, Hunan beef, and eat until it is gone, as others may try to eat it also. The quantity of Hunan beef in the tray is the decreasing concentration of oxygen in the diagram. Only after oxygen is gone does the next electron acceptor, nitrate, begin to work (or I start eating sesame chicken). I then proceed, in turn, to General Tso’s chicken (manganese) and then to Szechuan beef (iron). The diagram does not show decreasing concentrations of manganic and ferric ions because it would be messy. Therefore, I explain the display of increasing concentrations of reduced manganous and ferrous ions, thus introducing the chemical equations. When my stomach space is extremely “reduced”and I feel bloated, I use carbon dioxide as an electron acceptor and undergo methanogenesis. My students then understand redox.