Development of a Measurement Instrument Using the Rasch Model to Assess Students’ Conceptual Understanding in Stoichiometry

This research aimed to evaluate students' conceptual understanding and identify alternative conceptions of stoichiometry using a diagnostic tool developed with the Rasch model. Conceptual understanding was categorized into three levels based on the difficulty of the content in the IPST textbook. At Level 1, students can write and balance chemical equations when reactants and products are known. At Level 2, students can calculate substance amounts in stoichiometric fit reactions. At Level 3, students can perform calculations for non-stoichiometric fit reactions. A 10-item, two-tier multiple-choice test was designed to assess these levels and identify alternative conceptions among 228 Grade 10 students in Thailand. The results revealed that 39.47% of students were at Level 1, demonstrating the ability to balance chemical equations. Several alternative conceptions were observed. At Level 1, a misconception was that stoichiometric coefficients had to remain equal before and after a reaction. At Level 2, students incorrected believed that 1 mole of any substance occupied 22.4 dm³ at STP. At Level 3, students misunderstood that the limiting reagent is always the reactant in a smaller quantity. This diagnostic tool provided valuable insights into students' learning gaps and holds potential as a standardized test for stoichiometry in the future.