CAUT Report

UniServe Science News Volume 8 November 1997

An Interactive Multimedia Package Designed to Improve Beginning Students' Understanding of Chemical Equations

Introduction

Reviews of alternative conceptions research (e.g. Garnett, Garnett & Hackling, 1995) indicate that it is difficult for introductory chemistry students to develop adequate conceptions of the unobservable entities (atoms and molecules) and events involved in chemical reactions. The difficulties students experience visualising the submicroscopic particulate nature of matter and the processes involved in chemical change represent a major barrier to the development of a scientifically valid understanding of many chemistry concepts. As a result, beginning students often exhibit a wide range of alternative conceptions about the molecular basis of chemical reactions and this subsequently affects their ability to write balanced equations, interpret the symbolic representations used in equations and solve problems based on equations.

Johnstone (1991) proposed that chemistry is taught at three levels. The macroscopic level is sensory and deals with tangible and visible phenomena (e.g. salt dissolving in water). The submicroscopic level provides explanations at a particulate level (e.g. disruption of the ionic lattice with ions, surrounded by water molecules, moving into solution). The symbolic level represents processes in terms of formulas and equations (e.g. NaCl(s) + H₂O(l) -> Na⁺(aq) + Cl^-(aq)). Johnstone believes that insufficient attention is given to understanding chemistry at the submicroscopic level and has pointed out the difficulty for students when teachers move quickly between these different levels.

From the available research evidence it appears that students have most difficulty in dealing with the submicroscopic which is, of course, outside their experience and can only be made accessible to students through the use of models, analogies or computer graphics. Interactive multimedia materials are ideally suited to the simulation of the submicroscopic/ particulate nature of matter in its various states and the processes involved in chemical change. Tasker, Chia, Bucat and Sleet (1996) have reported recently on the VisChem Project which has developed molecular animations of a range of chemical processes aimed at improving students¹ understanding of the molecular basis of these processes.

Description of the project

This project developed an interactive multimedia package designed to help beginning students understand the particulate basis of chemical reactions, their symbolic representation as chemical equations and to apply this understanding when balancing equations and solving simple problems based on equations.

The materials were designed to expose students to the three levels of chemical knowledge described previously, i.e. the macroscopic, submicroscopic and symbolic levels, and provide an understanding of the particulate basis of chemical reactions. As well it was intended that the program provide opportunities for students to learn and practise the skills of balancing chemical equations. Finally the program aimed to develop students' skills in interpreting chemical equations at a quantitative level including an understanding of the concept of limiting reagent.

The project has developed three discrete modules that introduce students to chemical equations and develop skills in balancing equations and their interpretation. The materials are designed for use in direct teaching, tutorial or self-instructional modes. Two modules deal separately with 'molecular' and 'ionic' equations. A third module provides students with practice in the interpretation of equations.

Modules 1 and 2 both include instruction relating to eight chemical reactions. For each of these eight reactions students can:

1. View a video demonstration transformed into computer images (Figure 1). These images are intended to show students the actual appearance of a reaction when it occurs in real life. The purpose of this macroscopic view is to provide a link between the real world and the submicroscopic/particulate models chemists use to interpret chemical reactions;
   
   
   
   

   Figure 1. Video of a laboratory demonstration of a chemical reaction.

   
   
   
2. View a simulation of the reaction at a particulate level (Figure 2); these animations use dynamic graphics that illustrate the behaviour of atoms and molecules and the transformations they undergo in chemical reactions. The animations are designed to represent, at a particulate level, the processes that occur during chemical reactions using information that is available about these processes. In some examples, where these processes are very complex, the process animations are simplified;
   
   
   
   

   Figure 2. Simulation of a chemical reaction at a molecular level.

   
   
   
3. Write a balanced chemical equation (Figure 3). Equations are used to represent chemical reactions at a symbolic level. Students are provided with a particular approach to the balancing of equations which enables them to scaffold their knowledge. In this interactive program students are provided with a word equation and are asked to enter the formulas of each of the substances involved. Feedback is provided in relation to the chemical formulas written and also on the coefficients used to balance the equations. An option allows students to enter the physical states of all the substances involved.
   
   
   
   

   Figure 3. Interactive program for learning to write chemical equations.

   
   
   

Practice sets of twenty additional reactions are provided with both these modules to give students further practice in writing balanced chemical equations.

In Module 3 students develop their understanding of what chemical equations represent and their skills in interpreting equations. They are asked to interpret equations by drawing "before" and "after" diagrams to represent what occurs in a chemical reaction (Figure 4); do simple calculations to develop an understanding of the meaning of coefficients in chemical equations; and write equations to represent reactions illustrated by "before" and "after" diagrams (Figure 5). The concept of limiting reagent is introduced in some sections of this module.

Figure 4. Drawing "before" and "after" diagrams to represent a chemical reaction.

Figure 5. Writing equations from "before" and "after" diagrams representing a chemical equation.

Conclusion

This IMM package was designed to improve students' understanding of the particulate/molecular basis of chemical reactions, and their ability to balance and interpret chemical equations. The provision of concrete representations of unobservable entities and processes, and the use of an interactive approach with associated feedback should facilitate students' achievement of scientifically acceptable conceptions of chemical equations and their application.

References

Garnett, Patrick J., Garnett, Pamela J. & Hackling, M.W. (1994) Students' alternative conceptions in chemistry: A review of research and implications for teaching and learning. Studies in Science Education, 25, 69-95.

Johnstone, A.H. (1991). Why is science difficult to learn: Things are seldom what they seem. Journal of Computer Assisted Learning, 7, 75-83.

Tasker, R.F., Chia, W., Bucat, R.B. and Sleet, R. (1996). The VisChem Project - visualising chemistry with multimedia. Chemistry in Australia, September 1996, 395-397.

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