Diffusive and Deterministic Transport in Gels

We present a novel lab for teaching diffusion and electrostatics in ionic solutions. Two challenging topics in our introductory university physics course with a bio focus are diffusion and electrostatics in salty solutions. In the diffusion unit, the students work through a laboratory in which they observe two dyes diffuse in agarose gels. In the second semester course, electrostatics is introduced and the students investigate and model interactions between charges in conducting solutions. We developed a new laboratory in which the students investigate the movement of dye molecules with different charges and sizes under electric field in agarose gels. In this lab, the students make observations in gels made with pure water, as well as in media prepared with salt and buffered solution. The lab also allows students to use image analysis to determine pH change, how far the dyes have traveled, the effect of additional ions in the solution on the dyes and their interactions in different media, the change in current over time, and to estimate the unknown molar mass of one of the dyes.