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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 9 Issue 1 (2004) pp 9-11

Microscale Environmental Chemistry, Part 3: The Oxidation of Fe (II) by Molecular Oxygen as a Function of pH

Arturo Fregoso-Infante, Jorge G. Ibanez,* Luis C. Gonzalez-Rosas, Elizabeth Garcia-Pintor

Centro Mexicano de Quimica en Microescala, Departamento de Ciencias, Universidad Iberoamericana, Prolongacion Reforma 880, 01210 Mexico, D.F. Mexico, jorge.ibanez@uia.mx
Received May 25, 2003. Accepted September 10, 2003.

Published online: 9 January 2004

Abstract. The oxidation state of a chemical species is often responsible for its environmental behavior. Natural or anthropogenic processes can often change an oxidation state. For example, the redox state of iron depends on the presence of oxygen. In the following experiments the influence of pH upon the oxidation of Fe(II) is investigated by bubbling air through an Fe(II) solution at different pH values. In the first part, a qualitative experiment is aimed at showing the influence of pH upon the production of an Fe(III) precipitate. In the second part, a quantitative experiment is performed by bubbling air simultaneously through a series of Fe(II) solutions at different pH values. The Fe(II) remaining at the end of the experiment is then analyzed by potentiometric titration. It is made clear that high pH values favor the oxidation of Fe(II), whereas low pH values retard it.

Key Words: In the Classroom; general chemistry; environmental chemistry; analytic chemistry

(*) Corresponding author. (E-mail: jorge.ibanez@uia.mx)

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Issue date: February 1, 2004

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