Coordinating procedural and conceptual knowledge to make sense of word equations: understanding the complexity of a ‘simple’ chemical task at the learner’s resolution

摘要

This paper discusses the conceptual demands of an apparently straightforward task set to secondary level students – completing chemical word equations with a single omitted term. Chemical equations are of considerable importance in chemistry, and school students are expected to learn to be able to write and interpret them. However, it is recognized that many students find them challenging. The present paper explores students’ accounts of their attempts to identify the missing terms, to illuminate why working with chemical word equations is so challenging from the learner’s perspective. 300 secondary age students responded to a 5-item exercise based on chemicals and types of reactions commonly met at school level. For each item they were asked to identify the missing term in a word equation, and explain their answers. This provided a database containing more than a thousand student accounts of their rationales. Analysis of the data led to the identification of seven main classes of strategy used to answer the questions. Most approaches required the coordination of chemical knowledge at several different levels for a successful outcome; and there was much evidence both for correct answers based on flawed chemical thinking, and appropriate chemical thinking being insufficient to lead to the correct answer. It is suggested that the model reported here should be tested by more in-depth methods, but could help chemistry teachers appreciate learners’ difficulties and so offer them explicit support in selection and application of strategies when working with chemical equations.