亜鉛の電位差滴定における滴定条件

概要

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The determination of zinc by potentiometric titration with potassium ferrocyanide was carried out under various titrating conditions in solutions acidified with sulfuric acid by using bimetallic electrode of the platinum-tungsten, and influences on titration were investigated. At 20°C, the titre at the end point varied with concentrations of sulfuric acid and ammonium sulfate. When it was carried out in a solution 0 to 0.05N with respect to sulfuric acid and 20 g of ammonium sulfate per 100 ml of solution on condition of the constant speed of titration, the reproducibility of the titration was readily assured and a typical potential curve was obtained with a sufficiently large potential change at the end point. 0.00250.0125M zinc solution was titrated with an average relative error of +1.5%. At 60°C, the titration was done very rapidly. Influences of concentrations of sulfuric acid and ammonium sulfate and of the time for titration were smaller although the potential change was also small. The titration error was about -1.2%. In the case of the reverse titration at 20°C, the titre at the end point was almost the same as that at 60°C. Influences of acid and sulfate concentrations were small as well, but the potential change at the end point was also small.
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