Determination of molecular size and Avogadro’s number: A student experiment Available to Purchase

In this paper we describe a simple and inexpensive student experiment for the estimation of molecular size and Avogadro’s number. The results are close to the accepted values. We use elementary kinetic theory and two pieces of experimental information. The diffusion length of iodine in air at 100 °C as a function of time is one piece of data used; the other is the change in volume of a given small quantity of carbon dioxide as it goes from the solid to the gaseous state. This experiment is an adaptation of Rogers’ demonstration experiment. For demonstration purposes one uses bromine diffusion in air at room temperature and the volume change upon evaporation of a small quantity of liquid nitrogen.