Distillates - EiC Jan 2012

Distillates - Chemical Education Research

David Read looks at recent chemical education research

Getting to grips with gases

A good understanding of the particulate nature of matter is essential for any student to grasp complex topics including entropy, equilibria and kinetics. Although primary school pupils typically learn about the behaviour of particles in different states of matter, with further reinforcement at 11-14 level, many able students still show poor understanding which inhibits progress at post-16 level.

Chiu and colleagues investigated students' understanding of the behaviour of particles in gases, and compared the results with teachers' predictions. The research centred on a computerised test which included dynamic elements which reveal characteristics of gas particles in some questions, allowing students to then select which representation most closely matched their own perception.

Students generally held one of three mental models: a) the weight model, where heavier particles tend to sink to the bottom of a container b) the size model, where larger particles push their way towards smaller ones (rather than vice versa) and c) the correct scientific model where particles become randomly distributed regardless of size and weight. The test examined whether or not students changed the model they applied when the orientation of the apparatus or the pressure was changed.

The study included reasonable sample sizes of 102 8th graders and 92 9th graders. Only a small percentage of students answered all questions correctly, and the 9th graders outperformed the 8th graders, as one might have expected. Interestingly, the teachers involved in the study made incorrect predications regarding students' answers, illustrating another impediment to teaching and learning in this area.The key finding is that the main misconception centres on a lack of knowledge of the random distribution of gas particles, which is in line with previous studies. The authors suggest that static images in textbooks may play a role in reinforcing this problem.

In their conclusions, the authors recommend that teachers identify their students' misconceptions more effectively to identify appropriate strategies, including the use of dynamic visual resources, to support progress.

References

J-C Liang et al, Chem. Educ. Res. Pract., 2011, 12, 238 (DOI: 10.1039/C1RP90029C)

Melting Misconceptions

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.

References

K C Smith and M B Nakhleh, Chem. Educ. Res. Pract., 2011, 12, 398 (DOI: 10.1039/C1RP90048J)

Demystifying bonding

Chemists use a complex combination of jargon and graphics to communicate information, and it should be no surprise that students can find it difficult to adapt to this new 'language' of multiple representations. Hilton and Nichols have carried out a study which probed students' understanding of different representations in relation to the vital topic of chemical bonding.

In their introduction, the authors revisit the suggestion that there are three levels of representation in chemistry; macroscopic, sub-microscopic and symbolic. They propose that students' misconceptions arise from the misguided use of different forms of representation by past teachers, adding to the mystery of chemistry rather than clarifying it. In particular, symbolic representations, communicating little information about underlying phenomena, can be problematic.

The research involved 49 Year 11 students, and was carried out in two phases. During the initial phase, students were taught about the use of representations in explaining and predicting phenomena relating to structure and bonding. Electronic learning resources, including ACD ChemSketch and Molecular Workbench (both freely available online), were used extensively for hands-on learning. This was followed by a second phase involving two investigations into the properties of biopolymers, where groups of students completed digital posters and lab reports in different orders. This allowed the researchers to examine students' abilities to use multiple representations in describing the behaviour of biopolymers at the molecular level.

Evidence from pre-test/post-test comparisons and scrutiny of their work showed that students' understanding of the phenomena underpinning their laboratory observations had been enhanced by the approach. Other interesting outcomes are evident in the comments of students themselves, many of which are included in the text. Students felt that generating and manipulating their own molecular-level models and diagrams was particularly valuable, and that the focus on multiple representations helped them to communicate with each other more effectively.

In the final conclusions, the authors suggest that teachers' own understanding of why they use particular representations is not always clear, and that a lack of focus can lead to misconceptions, with implications for teacher training and professional development.