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以碘化钾标准溶液为滴定剂沉淀滴定法测定银,存在大量钨、钼、硅酸有干扰。通常采用氯化银沉淀预分离,再以氨水溶解后滴定。可是,此时连同沉淀的钨、钼、硅酸等也溶解,溶液发生混浊,致使滴定终点不明显,不适宜分析银含量在0.0x%的试样。经试验作了三点改进:在40毫升待沉淀溶液中银量应多于100微克,采用氯化银饱和溶液稀释和洗涤沉淀;用硫代硫酸钠溶液代替氨水溶解沉淀,可与钨、钼、硅酸等分离,又避免了氨嗅;滴定前溶液中加入适量碘乙醇溶液,使碘浓度≥1.8×10~(-5)M,终点则明显且与等当点一致。分析步骤称取1.000～3.000克试样(视银含量
Potassium iodide standard solution as titrant precipitation titration silver, there is a large number of tungsten, molybdenum, silicate interference. Usually silver chloride precipitation pre-separation, and then dissolved in ammonia after titration. However, the precipitated tungsten, molybdenum, silicic acid and the like are also dissolved at this time, and the solution is turbid, resulting in the end point of the titration being not conspicuous. Therefore, it is not suitable to analyze the sample with a silver content of 0.0x%. The experiment made three improvements: in 40 ml of solution to be precipitated silver should be more than 100 micrograms, the use of silver chloride saturated solution dilution and washing the precipitate; sodium thiosulfate solution instead of ammonia dissolved precipitate, with tungsten, molybdenum, Silicic acid and other separation, but also to avoid the ammonia sniff; titration solution before adding iodine ethanol solution, so that the iodine concentration ≥ 1.8 × 10 ~ (-5) M, the end point is obvious and with the same point. Analysis step Weigh 1.000 ~ 3.000 grams of sample (depending on the silver content