Award Date


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Chemistry and Biochemistry

First Committee Member

MaryKay Orgill

Second Committee Member

David Hatchett

Third Committee Member

Paul Forster

Fourth Committee Member

Stefani Relles


Laboratory activities are a prevalent and essential part of chemistry learning because of their potential to help students develop problem solving abilities, visualize chemistry concepts learned in lecture, and gain practical skills. However, learning in the laboratory environment is not without its challenges. For example, cookbook-style chemistry laboratories can promote superficial learning, and cognitive overload can result from the study of new concepts and the use of new procedures in this environment. Multiple pedagogies and supports have been developed to address challenges such as these. The current research focuses upon external representations that are commonly used to support learning in the general chemistry laboratory. External representations are visual tools—such as graphs, pictures, charts, and equations—that are used to illustrate, model, and communicate ideas. These representations are often used in chemistry lecture and laboratory to illustrate concepts that are beyond the senses. Although external representations are used with the intent of supporting student learning, research indicates that students have difficulty interpreting and learning from them. Therefore, it is important to examine how students’ learning from these figures, graphs, and symbols correlates with what their instructors intend for them to learn.External representations are commonly used in the chemistry laboratory environment; however, very few studies have examined what instructors intend for their students to learn from these external representations, what is possible for students to learn from these external representations, and what students actually learn from these representations. Specifically, I focus on external representations of acid-base titrations. I have chosen this subject because titrations are an important skill for practicing scientists; therefore, it is important that students master titrations during their training. Furthermore, external representations are commonly used (1) to illustrate how students should set up their laboratory equipment, (2) to demonstrate how to carry out a titration, and (3) to help students understand the chemical reactions that occur during a titration. This research utilizes variation theory to determine what instructors intend for their students to understand about acid-base titrations, what they can learn from the images we use to instruct, and what they ultimately do learn about acid-base titrations. In this dissertation, I first describe the 18 features which instructors deem as critical for their general chemistry students to understand about acid-base titrations. These include pH, chemical equations, and excess base, among others. The images the instructor participants then chose to share with the student participants included most of the critical features mentioned by the instructors, indicating that typical images used to teach students about acid-base titrations are consistent with the concepts that instructors want their students to understand about titrations. Students were interviewed about their understandings of acid-base titrations both before and after viewing the external representations selected by the instructors. Evidence suggests that students learned from the representations. In fact, the external representations used in the study facilitated learning. The external representations used in the study facilitated learning for many of the critical features; in some cases, they were essential for learning. Therefore, it is critical that external representations used to teach acid-base titrations are chosen with consideration to the critical features identified by instructors, the affordances that the representations can give for learning, and the features that students focus upon when learning about these important chemistry concepts. Based on the findings of the current study, recommendations are provided for the design, the selection, and the utilization of external representations used in teaching acid- base titrations.


Acid-base titrations; Chemistry education; Variation theory


Chemistry | Science and Mathematics Education

File Format


Degree Grantor

University of Nevada, Las Vegas




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