Distillate: David Read looks at recent chemical education research

Ice creams melting

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Dissolving and melting are phenomena that children become familiar with very early on. However, in a study by Smith and Nakhleh, good reasoning regarding what is happening on a particle level is something which eludes even some postgraduate students. It is not surprising that students form misconceptions about these processes, as an accurate description requires detailed knowledge of complex concepts such as bonding and intermolecular forces. This article indicates that misconceptions can persist even in the minds of advanced students.

A total of 23 undergraduates and 7 postgraduates were interviewed during the course of the study. In order to probe their understanding, the students were presented with samples of salt, chalk, sugar and butter and were asked to predict what they would observe and give detailed sub-microscopic explanations regarding the melting of these substances. Subsequently, water and cooking oil were added to separate samples of the same materials to test students’ understanding of dissolving. They were again required to predict the outcome and give a detailed explanation.

The article includes numerous quotes from students, which give a fascinating insight into the misconceptions they hold, and will be of genuine value to anybody teaching about these processes and the underpinning concept of intermolecular forces. Examples relating to dissolving are particularly informative. These include the ideas that solvents form ionic or covalent bonds with particles in the solute and that oil molecules form hydrogen bonds to carbon-hydrogen bonds in the molecules in butter.

This article not only gives a framework which teachers can use to identify their students’ misconceptions, but also gives suggestions for teaching strategies to correct them. These include the use of models and animations, as well specific practical experiments and demonstrations which teachers may use to effectively communicate ideas and the explanations behind them.