Students' conceptions of stoichiometry at the submicro level

Abstract

Stoichiometry is an important topic in chemistry. It tells how many reactants are required to produce a certain amount of product in terms of mass, mole and volume. Learning stoichiometric calculation involves the understanding of certain concepts such as the mole, stoichiometric ratios and chemical equations. Some studies attributed the failure in learning stoichiometry to the unfamiliarity with the amount of substance in a mole and students’ weakness in the mathematical ability. Nevertheless how students connect the submicro level and the symbolic level in learning stoichiometry was not discussed widely. In this study, two examples of chemical reactions with different levels of difficulties were used to probe students’ conceptual understanding in stoichiometry at the submicro level. Their strategies used in stoichiometric calculations were examined by an interview study of five Secondary Five students. The connection between the submicro level and the symbolic level in learning stoichiometry would be also probed into. Results indicate that the failure of stoichiometry learning may due to the disconnection in different levels of representation and students’ generated strategy – ‘one portion reasoning’. An implication for teaching and learning is that teachers should use diagrams at the submicro level in the teaching of stoichiometry. Such diagrams should aim to help students building connections across the three levels of representation and enhancing students’ conceptual understanding in stoichiometry.