This process standardizes EDTA solutions through titration with sodium hydroxide, enhancing understanding of chemical equilibrium.
EDTA solutions prepared with Na2H2Y•2H2O in the concentration range of 0.1 to 0.01 mol L–1 were standardized alkalimetrically with sodium hydroxide solutions by titrating the hydrogen ions released by the reaction of excess Ba2+ or Ca2+ ions with hydroxide ions. Equilibrium constants estimated for the overall reaction are K = 2.2 × 1019 mol–3 L3 for Ba2+ and 2.2 × 1022 mol–3 L3 for Ca2+. Endpoints were found with phenolphthalein or by using potentiometric derivative curves plotted from data measured with a glass electrode. This gave an opportunity for helpful discussions with students concerning the involvement of chemical equilibrium in the fundamentals of the method, and it has been found to be a good didactic example for dealing with equilibrium constants.
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Neves et al. (2005) studied this question.
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