The ability to "engage in argument from evidence" is one of the eight practices identified in the "Next Generation Science Standards" as well as an emerging focus of undergraduate chemistry curricula. Guiding students to make evidence-based claims that engender argumentation will require faculty to revise conventional expository laboratory experiments. The type of data collected and the method of collecting the data as well as the question to be answered must be carefully considered. This paper describes a simple yet effective change to a standard laboratory, the determination of density, which we have used since 2006 to engage students in argumentation about both method and outcomes.