Ceric oxalate, Ce(C₂O₄)₂

Ceric oxalate, Ce(C₂O₄)₂.7H₂O (?). - Ceric oxalate is obtained as an orange-yellow gelatinous precipitate when cold, aqueous solutions of ceric ammonium nitrate and ammonium oxalate are mixed. The precipitate is difficult to filter and wash, and when attempts are made to dry it on a porous plate, considerable decomposition occurs; apparently a mixture of cerous oxalate, Ce₂(C₂O₄)₃.10H₂O, and ceric oxalate, Ce(C₂O₄)₂.7H₂O, is produced, from which ceric oxalate may be extracted with aqueous ammonium oxalate. Cerous oxalate is a very unstable salt, readily losing carbon dioxide and becoming converted into cerous oxalate: -

2Ce(C₂O₄)₂ = Ce₂(C₂O₄)₃ + CO₂.

It is readily soluble in ammonium oxalate solution, thereby resembling thorium oxalate. The orange-yellow solution deposits cerous oxalate on standing, the decomposition being rapid when the solution is warmed. The cerium may be rapidly and quantitatively precipitated from the solution by the addition of sulphurous acid.