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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 10 Issue 5 (2005) pp 367-370

Standardization of EDTA Solutions Using an Alkalimetric Method: Didactic Aspects

Eduardo Almeida Neves, Andrea Oliveira, and Joaquim A. Nóbrega*

Departamento de Química, Universidade Federal de São Carlos–São Carlos. Via Washington Luiz km 235, São Carlos, SP. CEP 13565-905, BRAZIL, djan@terra.com.br
Received April 30, 2005. Accepted July 21, 2005.

Published online: 21 September 2005

Abstract. 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.

Key Words: Laboratories and Demonstrations; quantitative analysis; titration; EDTA standardization; alkalimetry; potentiometry; calcium; barium; equilibrium constants

(*) Corresponding author. (E-mail: djan@terra.com.br)

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Issue date: October 1, 2005

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