It makes more sense honestly to dissolve BaO2 with aqueous HCl (recalling that peroxide is stabilized by acid), titrate to pH 4-5ish with a solution
of Na2CO3, collect dilute peroxide by distillation, and then convert the remaining BaCl2 to the carbonate by adding water followed by more Na2CO3
until precipitation ceases. HCl and Na2CO3 are pretty cheap. |