Many studies in science education research have found metacognition to be beneficial for undergraduate STEM students. Students do not necessarily know how to employ their metacognition without some training or prompting, and undergraduate chemistry instructors do not always have the capacity to instruct their students on metacognition. Thus, it would be beneficial for instructors and students if metacognition development could be implicitly incorporated into typical classroom activities. In this study, 25 undergraduate students in an upper-division biochemistry course were interviewed via a think-aloud protocol. In the interviews, they were asked to solve two open-ended buffer problems. Before answering the second buffer problem, the students were asked questions designed to target their metacognition. The interview transcripts were qualitatively analyzed through a codebook thematic analysis, with deductive and inductive coding, to understand the types of metacognitive knowledge and metacognitive skills these students demonstrated while solving the buffer problems. The transcripts were also analyzed to understand how these metacognitive prompts may have changed students' metacognitive approaches to solving the problems. Overall, 20 of the 25 students demonstrated some type of metacognition in response to the metacognitive prompts that they had not demonstrated in the first buffer problem. We discuss how asking students to think how an "unreflective" student would answer a question can prompt students to metacognitively evaluate their thought processes.