EDTAによる鉄(III)の双金属極電位差滴定

概要

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Potentiometric titration of iron(III) with EDTA was carried out both in the solution acidified with hydrochloric acid and in the acetic acid-sodium acetate buffer solution by use of eight couples of bimetallic electrodes: platinum-tungsten, platinum-palladium, platinum-molybdenum, platinum-silver, platinum-silver amalgam, platinum-gold, platinum-zirconium and platinum-nickel. Titration curves were constructed and the magnitudes of change in potential at the end point were compared. Platinum-tungsten, platinum-gold and platinum-palladium electrode couples showed reverse L-shaped titration curves and the potentials at the end point increased abruptly. Platinum-molybdenum electrode couple presented a titration curve having a peak. The other four electrode couples gave reverse S-shaped titration curves and the potentials at the end point receded suddenly. Platinum-molybdenum and platinum-nickel electrode couples showed a deviation of end point in the solution acidified with hydrochloric acid (pH 2.1), and, accordingly, were not suitable for the titration. In the titration of iron(III) with 0.01M EDTA, platinum-tungsten electrode couple was applicable with good results at pH 2.78. The magnitude of ΔE/ΔV at the end point for this couple in 0.01M solution was greater than that in 0.1M solution, but the reason was not clarified.
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