Lanthanum oxalate, La₂(C₂O₄)₃

Lanthanum oxalate, La₂(C₂O₄)₃.9(10 or 11)H₂O, may be obtained by double decomposition as a white, crystalline precipitate. According to the temperature at which precipitation occurs and the temperature of the wash water, the precipitate appears to contain 9, 10, or 11H₂O. Most experimenters give 10H₂O as being present in the hydrate in equilibrium with its aqueous solution at 25°.

Lanthanum oxalate is appreciably soluble in a solution of lanthanum nitrate, but no crystalline oxalonitrate can be isolated at 25°. The only hydrates of lanthanum oxalate that are stable at 25° in contact with aqueous solutions of lanthanum nitrate of the appropriate concentrations are those containing 3H₂O, 5H₂O, and 8H₂O. A hydrate containing 7H₂O may be crystallised from dilute sulphuric acid.

A solution of lanthanum oxalate in hot, concentrated hydrochloric acid deposits crystals of lanthanum oxalochloride, 2La(C₂O₄)Cl.5H₂O, when cooled. The salt is decomposed by water.