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Educational research High school students’ understanding of titrations and related acid- base phenomena Keith Sheppard Program in Science Education, Teachers College, Columbia University, 525 West 120th Street, New York, NY, 10027, USA e-mail: sheppard@tc.columbia.edu Received 26 November 2005, accepted 4 January 2006 Abstract: Acid-base titrations are common laboratory activities carried out in high school chemistry courses. Using a series of qualitative and computer-based tasks, this study examined sixteen American students’ understanding of titrations. The findings indicated that students had considerable difficulty with acid-base chemistry, were unable to describe accurately acid-base concepts, such as pH, neutralization, strength, and the theoretical descriptions of acids and bases. Further, most students could not relate the concepts to actual solutions. Student difficulties stemmed from a lack of understanding of some underlying chemistry, such as the nature of chemical change and the particulate nature of matter. A number of factors were identified as contributing to these difficulties, including the overstuffed nature of introductory chemistry itself, the emphasis during instruction on solving numerical problems, and the dominant role played by the textbook. The conceptual density of acid-base chemistry, the confusing nature of acid-base terminology and the lack of agreement about what material should be included in the chemistry curriculum were identified as being problematic. [Chem. Educ. Res. Pract., 2006, 7 (1), 32-45] Keywords: Acid-base models, titration, pH, neutralization, student conceptions Introduction Acid-base titrations are common exper