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一问题的提出 1 标定硫代硫酸钠标准溶液,常用的基准物是纯铜和重铬酸钾。实践表明两种基准物标定出的浓度相差很多,通常是以纯铜为基准物标定出的浓度偏高。 2 以纯铜为基准物标定出的浓度用于计算铜合金标样的含铜量分析结果时,也往往误差过大。 3 碘量法定铜接近终点时,加入硫氰酸盐溶液,有时溶液颜色变浅,甚至完全变白(终点提前),有时终点颜色带灰包,致使色泽变化不敏锐。以上问题均由硫氰酸盐中的耗碘杂质(主要是硫化物利氰化物)所致。硫化物不仅耗碘而且能与一些
A proposed problem 1 calibration of sodium thiosulfate standard solution, the common benchmark is pure copper and potassium dichromate. Practice shows that the two standards to determine the concentration of a lot of difference, usually based on pure copper as the standard calibration of the high concentration. 2 copper as the benchmark to determine the concentration of the standard for the calculation of copper alloy copper content analysis results, it is often too much error. 3 Iodine legal copper near the end, adding thiocyanate solution, and sometimes the solution lighter color, or even completely white (end point ahead of time), sometimes the end of the color with a gray pack, resulting in less sensitive to changes in color. The above problems are caused by consumption of iodine impurities in thiocyanate (mainly sulfides cyanide). Sulfides not only consume iodine but also some