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镀铬液中硫酸根的测定通常采用硫酸钡重量法、硫酸钡沉淀-EDTA 容量法。前者速度慢,后者准确度欠佳。Natarajan 的方法是先用苯甲酸银使铬生成铬酸银沉淀而将铬分离,然后用 EDTA 测定滤液中的硫酸根。Norwitz 用氢碘酸、次磷酸将硫酸根还原成硫化氢以后吸收在氨水中,在加入柠檬酸铅后,用光度法测定硫化铅的黄褐色。最近,Prasad报道,也采用苯甲酸银使铬酸根沉淀分离,然后用阳离子交换树脂除去银和钠离子,在加抗坏血酸后用钡电极为指示电极、高氯酸钡为滴定剂滴定硫酸根。
Determination of sulfate in the chrome plating solution usually barium sulfate gravimetric method, barium sulfate precipitation-EDTA capacity method. The former is slow, the latter less accurate. Natarajan’s method is to first separate the chromium from the silver by silver benzoate precipitation of chromium silver and then measure the sulfate in the filtrate with EDTA. Norwitz uses hydroiodic acid and hypophosphorous acid to reduce the sulfate to hydrogen sulfide and then is absorbed in aqueous ammonia. After the lead citrate is added, the yellowish brown color of the lead sulfide is measured spectrophotometrically. Recently, Prasad reported that silver chromate was also precipitated using silver benzoate and silver and sodium ions were removed by cation exchange resins. After ascorbic acid was added, the barium electrode was used as the indicator electrode and barium perchlorate was used as the titrant to titrate the sulfate.