Precipitation and puddle chemistry

Abstract

In order to be accepted as a useful technique in practical chemistry, the microscale technique has to offer more to the teacher and students than the traditional method. This account of diffusing precipitates shows that the understanding of the mechanism can be enhanced with extremely simple equipment. The technique uses worksheets which are laminated or inside a polypropylene folder, so the student can see the instructions, while at the same time placing puddles of water or solutions on the plastic hydrophobic surface. Salts are added to the puddle, dissolve and migrate via diffusion to form a line of insoluble salt. An examination of the mechanism for precipitation incorporates a discussion on the Johnstone Triangle, encompasses many of the core ideas of chemistry developed by Professor Peter Atkins and the amazing videos produced by Roy Tasker. It shows how even the wording of exam syllabuses can be influenced by descriptions of events at the nano-level, and the relevance of precipitation to students. The evidence of solvated ions is demonstrated by a simple conductivity indicator. This article is based upon a keynote lecture given at the 10th International Symposium on Microscale Chemistry (ISMC) held at the University of the North West, Potchefstroom, South Africa.