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在定量分析化学中,标化0.1 N 的碘溶液,一般均以三氧化砷(As_2O_3)或0.1 N 的硫代硫酸钠溶液为基准物质;在中国药典1953年版中亦规定以三氧化砷为原始标准。惟因三氧化砷的毫克当量为49.46,标化0.1N 碘液时所取之量约为150毫克;在—般化验空中天平的敏感度仅为~1/_(10,000)克或更低于此时,则秤量150毫克,每易引起差误。今年5月份分析化学杂志(Analytical Chonistry,1953,25,767)中,载有“以一结晶水硫代硫酸钡标化碘溶液”一文;因其毫克当量为267.5,标化0.1N 碘液时所取之量约为900毫克左右;如此则因秤量而产生之差误当可减少。今将原文及本人仿照实验的结果介绍于下:
In quantitative analysis of chemistry, standardization of 0.1 N iodine solution, usually with arsenic trioxide (As2O3) or 0.1 N sodium thiosulfate solution as the reference substance; in the Chinese Pharmacopoeia 1953 edition also provides for arsenic trioxide standard. However, since the arsenic trioxide has a meq of 49.46 and an amount of about 150 mg is taken when standardizing 0.1 N iodine solution, the sensitivity to a typical airborne balance is only ~1 / _ (10,000) grams or less At this point, then weighing 150 mg, each can cause errors. In May this year, Analytical Chonistry (1953, 25, 767) contained a paper titled “Iodine Solution with Barium Sulfate in a Crystallized Water”; with a milliequivalent of 267.5 normalized 0.1N iodine solution The amount taken is about 900 mg; so the error caused by the weighing can be reduced. Now the original text and I follow the experimental results introduced in the next: