Gravimetric determination as barium sulphate after distillation

2 Gravimetric determination as barium sulphate after distillation General 

The sulphite ions are distilled over as sulphur dioxide from a solution containing phosphoric acid into a receiver containing a solution of iodine and potassium iodide, where they are oxidized to sulphate ions  

The sulphate ions are precipitated out of the weakly acid solution as barium sulphate by adding barium chloride solution, and then weighed. 

The method is suitable for determining sulphite ions in concentrations in excess of 20 - 30 mg/1 and where considerable quantities of disturbing 

The distillation process largely eliminates any disturbing factors. 

---