Here we describe an experiment for the undergraduate physical chemistry laboratory in which students synthesize the intermetallic compounds AlNi and AlNi3 and study them by X-ray diffractometry. The compounds are synthesized in a simple one-step reaction occurring in the solid state. Powder X-ray diffractograms are recorded for the two compounds as well as for the elements Al and Ni, all of which have cubic crystal structures. The students analyze the measured spectra to determine both the type of cubic lattice present and the unit cell dimension for comparison with the literature. The experiment demonstrates the utility of X-ray diffraction for structure determination.