UPPER SECONDARY SCHOOL STUDENTS’ CONCEPTIONS OF CHEMICAL EQUILIBRIUM IN AQUEOUS SOLUTIONS: DEVELOPMENT AND VALIDATION OF A TWO-TIER DIAGNOSTIC INSTRUMENT

Student understanding of chemical equilibrium in aqueous solutions (CEAS) plays a vital role their upper secondary school chemistry learning and everyday life. Diagnosis students’ alternative conceptions (ACs) the CEAS will provide teachers with valuable information to make instructional decisions on student learning. This study aims develop validate an instrument diagnose ACs about CEAS, including ionization equilibrium, water self-ionization salt hydrolysis, precipitation dissolution equilibrium. Using Treagust (1998)’s development framework, we have developed 25 two-tier multiple-choice items for diagnostic test. After completing corresponding courses, 750 Grade 11 students from five public schools responded Rasch modeling approach was employed psychometric properties test consisting one-dimensionality, reliability, validity. identified 15 toward CEAS. found that most performed better concept tiers rather than reasoning tiers. In addition, difficulties connecting acidity, solubility, ionization, reaction using mathematical thinking do transformation between concentration, constant, pH value. Keywords: solutions, conceptions, items,