Standardization of EDTA Solutions Using an Alkalimetric Method: Didactic Aspects

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

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 L³for 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)

Article in PDF format (285 KB) HTML format

Supporting Materials: