Secondary school students’ strategies in stoichiometry

This study was designed (1) to analyse the relationship between the answer profile from multiple‐choice questions on stoichiometric problems and the students’ reasoning patterns and (2) to examine the effect for certain variables on the facility values of test items. The instruments used were mainly paper‐and‐pencil tests. The subjects were 6262 grammar school students from all parts of the Federal Republic of Germany. They were randomly assigned to the test items. The results indicated that many students arrived at their answers by mixing up amount and reacting mass, or molar mass and reacting mass. It was also found that the variables ‘easy/hard calculations’, and ‘formula given/to be developed’ determined the facility values of test items. From the results, it was possible to make recommendations to practising teachers as well as to examiners. Knowing students’ ideas, the teacher can think of how to make use of them before entering the classroom. A teaching unit may start off with easy problems leaving the more difficult ones for later. Examiners developing new tests on stoichiometry should consider two essential preconditions for the formulae of chemical compounds, used in the item: formulae of the type AB should be avoided and the molar masses of the elements involved must be clearly different.