Exploring students' pre-instructional ideas in balancing chemical equations

Abstract

This study explored pre-instructional ideas of balancing chemical equation held by students aged 14-15 (Year 9). Nine students were selected based on their performance in a selection test that assessed their relevant prior knowledge of stoichiometry. Each three were selected from high, medium and low achievers in the test. These students were interviewed. Their pre-instructional ideas were probed into through observing strategies they employed in balancing a simple molecular equation (namely, the combustion of methane). It was found that students’ pre-instructional ideas of ‘being balanced’ varied. Strategies students deployed in balancing the equation could be modelled as using (1) symbols, (2) particulate drawings, and (3) numbers:

(1) Students deploying strategies using symbols tended to balance the equation successfully. But changes of subscripts in chemical formulae to represent the number of atoms was observed. (2) Students deploying strategies using particulate drawings demonstrated more use of relevant prior knowledge and the ability to move across symbolic representations and particulate diagrams. (3) Students deploying strategies using numbers were found to assemble very limited relevant prior knowledge of stoichiometry by treating the chemical equation as a mathematical equation.

The study ascertained students’ pre-instructional ideas in equation balancing and enhanced our understanding of what relevant prior knowledge was used as they attempted to balance the equation. Suggestions in the teaching of balancing equations in relation to students’ pre-instructional ideas are discussed.