Applications involving oxidation with KBrO3: Potentiometric determination of some inorganic white and yellow pigments

Rapid potentiometric methods were given for determination of some sulfide and chromate pigments in pure as well as adulterated samples. The methods are based on oxidation of S^2? or Cr³⁺ with known excess of KBrOs³ to the corresponding (S ↓) or Cr^6?. Oxidation of trivalent chromium proceeds only toward completion in presence of a catalyst such as Co²⁺. Sulfide oxidation needs gradual liberation of H₂S—which can be achieved by dropwise additions of the acid—together with the presence of excessive amount of water, in order to obtain accurate results excess oxidant was subsequently reduced with SO₂ to produce Br^? that can be titrated against Hg(I). The potential breaks are quite sharp for accurate determination of the equivalent points.