Major Sources of Difficulty in Students' Understanding of Basic Inorganic Qualitative Analysis

Abstract

Most students' introduction to qualitative analysis in the United States occurs in general chemistry courses at college or university; in Australian universities this occurs as part of analytical chemistry courses for chemistry majors. In Singapore, however, students are first introduced to qualitative analysis in grade 10 chemistry (when they are 16 years old), even though the topic is generally considered to be conceptually difficult to understand and there is inadequate time for comprehensive experimental work. Using extensive interviews, this study was designed to identify the sources of these difficulties. Students had difficulty understanding the formation of precipitates and complex salts, and the reactions of acids in qualitative analysis experiments. Many students thought that the formation of precipitates in reactions involving exchange of ions was because of more-reactive ions displacing less-reactive ones, and that ammonia was included in the reactivity series. The students also regarded the formation of complex salts such as zincates as a mere dissolution process, and did not understand the reactions involving acids; for example, they thought that neutralization reactions involved redox processes, and that the order in which acids were added determined whether unknown anions could be identified. Instructional implications arising from the study are discussed.