Although vacuum technology is essential to many aspects of modern physical and analytical chemistry, vacuum experiments are rarely the focus of undergraduate laboratories. We describe an experiment that introduces students to vacuum science and mass spectrometry. The students first assemble a vacuum system, including a mass spectrometer. While assembling the vacuum system students learn about the components and the conditions necessary to operate a mass spectrometer. Then students use their assembled system to explore mass spectrometry; they use the mass spectrometer to diagnose vacuum conditions, then collect the mass spectrum of an unknown organic molecule, and propose the identity of the molecule.