Semi-Permiable Membranes: How Molecule Size Affects Diffusion Rate

Abstract

This experiment is a look at how diffusion and osmosis work, and what possibly limits diffusion. Specifically, in this experiment we are interested in how the size affects how much of a molecule can move across a semipermeable membrane. Previous work has not specifically addressed whether or not molecules move across membranes by observing a change in mass, volume, and concentration. As a result, we chose to observe the amount of three different sized molecules that diffuse across a semi permeable membrane. We hope to accomplish this by observing mass, volume, and concentration of the molecule in the solution surrounding the semipermeable membrane. We tackled this question by running several tests, using dialysis tubing to represent a semipermeable membrane, and recording the mass, volume, and concentration of the solute in the outside solution to observe how the size of molecules affects how much, if at all, the molecules diffuse across the membrane. By observing what can and cannot cross a membrane, this could possibly assist future researchers in developing artificial cells, and eventually recreating organs, such as kidneys.