Relationship between Students’ Knowledge Structure and Problem-Solving Strategy in Stoichiometric Problems based on the Chemical Equation

Relationship between students’ knowledge structure and problem-solving strategy was studied using a written test containing one complex stoichiometric problem based on the chemical equation and four simple problems similar to the steps of two known strategies (mole method and proportionality method) for solving the complex problem. Based on the strategy used in solving the complex problem students (N = 1072, grades 7-10) were divided into three groups: (1) mole method group; (2) proportionality method group; and (3) others (unidentified strategy or no strategy). The knowledge structure characteristic of each group was determined by using knowledge space theory. There was no significant difference between the success (ca. 70%) of the student groups applying any strategy (groups 1 and 2), but the achievement of the students not using any strategy (group 3) was significantly lower (ca. 20%). We found significant difference between the characteristic knowledge structure of the three groups. The knowledge structure of the group 3 is very similar to the experts’ knowledge structure. However, the knowledge structure of the student groups using any strategy shows that students typically used these problem-solving strategies as algorithms instead of the conceptual understanding. For example in the characteristic knowledge structure of group 1 the knowledge necessary to solve the complex problem is built on both the proportionality and the molar mass, while in case of the student group 2 it is built on only one simple knowledge, the proportionality.