Mosander went to school in Kalmar until he moved to Stockholm with his mother at age 12. There he became an apprentice at the Ugglan pharmacy. He took his pharmacy examination in 1817, but had an interest in medicine and matriculated as a student in the Karolinska Institute in 1820 and graduated with his Master of Surgery degree in 1824. He worked teaching chemistry at the Institute and as an assistant in the mineralogical collection of the Swedish Museum of Natural History. Jöns Jakob Berzelius was his teacher of chemistry during his medical studies, and in 1836 he succeeded him as professor of chemistry and pharmacy in the Karolinska Institute. Lanthanum was discovered in 1839 by Mosander, when he partially decomposed a sample of cerium nitrate by heating and treating the resulting salt with dilute nitric acid.