The characterization of students' cognitive biases is of central importance in the development of curriculum and teaching strategies that better support student learning in science. In particular, the identification of shortcut reasoning procedures (heuristics) used by students to reduce cognitive load can help us devise strategies to foster the development of more analytical ways of thinking. The central goal of this study was thus to investigate the reasoning heuristics used by undergraduate chemistry students when solving a traditional academic task (ranking chemical substances based on the relative value of a physical or chemical property). For this purpose, a mixed-methods research study was completed based on quantitative results collected using a ranking-task questionnaire and qualitative data gathered through semistructured interviews. Our results revealed that many study participants relied frequently on one or more of the following heuristics to make their decisions: "recognition," "representativeness," "one-reason decision making," and "arbitrary trend." These heuristics allowed students to generate answers in the absence of requisite knowledge; unfortunately, they often led students astray. Our results suggest the need to create more opportunities for college chemistry students to monitor their thinking, develop and apply analytical ways of reasoning, and evaluate the effectiveness of shortcut reasoning procedures in different contexts. (Contains 2 tables and 2 figures.)