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Abstract

The authors' purpose in a series of two investigations is to examine the following research questions: (1) How do college students define the mole concept? (2) How do college students explain the numerical identity between the atomic or molecular mass of a substance and its molar mass? (3) Is there a connection between students' definitions of the mole concept and their explanations of the numerical identity between the atomic or molecular mass and the molar mass of a substance? (4) Do the connections in question 3 extend to students' ability to solve mole concept problems? Research questions 1-3 are examined first through an analysis of students' answers and errors on a chemistry examination question that assesses their knowledge of the mole concept and the numerical identity between the atomic or molecular mass of a substance and its molar mass. Forty-eight students in the first quarter of first-year chemistry for scientists and engineers at a large, urban, midwestern research university during summer session are the subjects. One question on the first exam assesses the extent to which students understand the mole concept and the above-mentioned relation. Results indicate that students' most frequent errors are: (1) failing to define the mole in terms of 12C; (2) defining the mole as Avogadro's number; (3) defining the mole as a mass; and (4) constructing a logical argument in vague terms or by using improper knowledge. The results and limitations of the first investigation prompted a follow-up study in which the authors add research question 4 and further examine research questions 1-3 through qualitative methods. In the second study, the subjects are 12 college students enrolled in a chemistry course for students with little or no background in chemistry. Each subject participates in a think-aloud protocol designed to focus on the research questions. The authors qualitatively analyze the content of written transcripts of the audiotaped think-aloud sessions. Results of the second investigation indicate that students' definitions of the mole vary and that their definitions are connected to their understanding of the numerical identity issue. Moreover, students' understanding of the numerical identity issue is a major stumbling block in terms of their ability to solve two problems in the think-aloud protocol. Results of both investigations are discussed in terms of research in chemical education and in cognitive science.