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The research reported in this case study explores the understanding of stoichiometry and related concepts of Thai science students in grades 10 and 11 after major national curriculum reforms. Students' conceptions and alternative conceptions were investigated using a questionnaire--the "Stoichiometry Concept Questionnaire" (SCQ) (N = 97), which consists of 16 multiple-choice items, the choices for which respondents are required to provide reasons. The findings suggest that less than half of the students surveyed hold what is considered by a panel of experts to be a scientifically acceptable understanding for the conceptions investigated. The main student alternative conceptions are that one mole of all substances has a volume of 22.4 L at STP, that a solution that contains a greater mass of solute has the higher molar concentration, and that the limiting reagent is the reagent for which the lowest mass of reactant is present. Examination of students' reasons suggests that they resort to the use of algorithms with little understanding of the underlying concepts. It thus seems the national educational reforms have not resulted in a sound understanding of some science concepts. It is recommended that curriculum developers should specify a need for conceptual understanding along with capability in numerical problem-solving in their learning objectives, and link this to assessment regimes that reward conceptual understanding. A need for on-going professional development seems essential if the intentions of the Thai curriculum reforms are to be realized.

The international literature suggests students frequently resort to the use of formulae when solving stoichiometry problems without understanding the concepts. In prior work we identified Thai student alternative conceptions and ability to solve numerical problem for stoichiometry. The results indicate that many Thai students also hold alternative conceptions and that their ability to solve numerical problems is related to their understanding of the concepts. In the present work we describe an intervention consisting of the development of a series of stoichiometry learning units (SLUs) based on a conceptual change approach. The units involve five steps: express ideas, share ideas, challenge ideas, accommodate ideas, and apply ideas. The SLUs were implemented by three volunteer teachers in three Grade 10 science classrooms from three different schools. The findings suggest that the conceptual change approach can be useful in addressing student alternative conceptions, developing student conceptual understanding, and enhancing students' ability to solve numerical problems. (Contains 5 figures.)

Stoichiometry and related concepts are an important part of student learning in chemistry. In this interpretive-based inquiry, we investigated Thai Grade 10 and 11 students' conceptual understanding and ability to solve numerical problems for stoichiometry-related concepts. Ninety-seven participants completed a purpose-designed survey instrument consisting of open-ended questions about stoichiometry-related concepts. Detailed analysis of the research findings suggest that most of the student participants held alternative conceptions similar to and different from those reported in the Western educational contexts. The alternative conceptions related to using a mole ratio as a mass ratio; identifying a limiting reagent as the least amount reactant; using 1:1 mole ratio for all substances in the equation; thinking that one mole of water was of 22.4 dm[superscript 3] in volume, and that the units mol/dm[superscript 3] represent the mole of solute per kilogram of solution. The students' ability to solve numerical problems seems to be related to their conceptual understanding of stoichiometry; students with alternative conceptions found it difficult to solve the problems relating to the concepts.