Graduate students play a critical role in undergraduate education at doctoral-granting institutions and yet their training is often brief and overgeneralized. Little is known about how they develop knowledge for teaching chemistry in this context. To further understand how graduate students develop knowledge for teaching, we used a questionnaire to measure pedagogical content knowledge of solution chemistry concepts. These concepts are revisited frequently in the undergraduate curriculum, particularly in laboratory courses where graduate students commonly teach. Questions were included to measure both the pedagogical content knowledge and content knowledge of graduate students with a range of teaching experience. Analysis revealed that graduate students' content knowledge is stronger than their pedagogical content knowledge, which increases modestly with teaching experience. Interviews were performed with a subset of respondents to determine whether they interpreted the questions as intended and the source of knowledge they used in responding. The interviews revealed that graduate students relied heavily on their own experience as students rather than direct experience teaching solution chemistry concepts.