Hydrated cobalt II nitrate; Co(NO3)2?H2O; Molar mass 291.03 g/mol Also known as cobalt II nitrate hexahydrate, cobaltous nitrate, Nitric acid, cobalt(2+) salt, hexaaquacobalt (II) nitrate Cobalt nitrate is an inorganic compound which forms when the maximum number of six water molecules attach to the cobalt ion. It is soluble in water as well as other polar solvents. If reduced, it becomes a high purity cobalt metal. It is used in Fischer-Tropsch catalysis and in the manufacture of inks and dyes.