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Fundamental Issues of Thermodynamics Illuminated by Conspicuous Inorganic Chemistry: Oxidation of [Co(H2O)6]2+ to [Co(H2O)6]3+ by Hydrogen Peroxide: A Nonspontaneous Redox Reaction Made Feasible by Thermodynamic Coupling

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Susan Cline Schäffer and Claus E. Schäffer

Undergraduate Department of Chemistry and Chemical Engineering, Technical University of Denmark, Building 375, DK 2800, Lyngby, Denmark

J. Chem. Educ., 1996, 73 (2), p 180

DOI: 10.1021/ed073p180

Publication Date (Web): February 1, 1996

Section:

History, Education, and Documentation

Abstract

The thermodynamic properties of hydrogen peroxide as an oxidizing agent do not allow it to oxidize [Co(OH2)6]2+ to [Co(OH2)6]3+. However, if [Co(OH2)6]3+ is formed in two steps, hydrogen peroxide is able to do it. The trick, which embodies two beautiful, classroom reactions, is to let the acid neutralization of HCO3- provide the driving force. The first step is the oxidation of pink [Co(OH2)6]2+ to green [Co(CO3)3]3-; the second one is the reaction of [Co(CO3)3]3- with acid to form the blue [Co(OH2)6]3+. The paradoxical reduction of [Co(OH2)6]3+ to [Co(OH2)6]2+ by H2O2, which is irrelevant for the thermodynamic discussion, forms an extra point in the demonstration experiment.

Keywords (Audience):

Upper-Division Undergraduate

Keywords (Domain):

Inorganic Chemistry

Keywords (Subject):

Thermodynamics

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Cobalt alums. A demonstration experiment
Claus E. Schäffer and Poul Steenberg , Wayne Wolsey and Erica Nostrom
Journal of Chemical Education2002 79 (8), 958
- Cobalt alums. A demonstration experiment
  Claus E. Schäffer and Poul Steenberg , Wayne Wolsey and Erica Nostrom
  Journal of Chemical Education2002 79 (8), 958
  The demonstration experiment describes the isolation of [Co(H2O)6]3+ both as the pure blue crystalline cesium cobalt alum, CsCo(SO4)2·12H2O, and as a light greenish-blue solid solution of ammonium cobalt alum in (NH4)Al(SO4)2·12H2O. The hexaaquacobalt(III)...
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