メチルレッドを指示薬とする亜鉛の新定量法

概要

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A new back-titrimetric method for the determination of zinc, using methyl red as an indicator is described. A sample solution containing zinc ions can be back-titrated by zinc chloride solution after an excess of potassium ferrocyanide solution has been added to the sample solution. Many kinds of indicators have been proposed for this titration. The authors propose methyl red as an indicator for this titration. The color change at the end point is sharp, and this can be used to advantage. After the sample solution containing the zinc has been neutralized to slight acidity by proper alkali or ammonia, the solution is heated to about 70°C, and 0.1 M potassium ferrocyanide solution is added beyond the equivalent point corresponding to the quantity of zinc in the solution. Then a few drops of methyl red solution are added as an end-point indicator. The excess of potassium ferrocyanide is back-titrated by 0.15 M zinc chloride solution. At the end point of the back titration, the color of the solution changes from white cream yellow to blue quite sharply. The titration curve, the pH changes in the process, and a schematic diagram of the circuit used for this titration are presented.
社団法人日本分析化学会の論文