Gibbs Free Energy of Formation of Synthetic Cryptomelane

Authors

  • Raphael Hypólito Universidade de Sao Paulo, Institute de Geociencias, Caixa Postal 20’899, BR - 01’000 Sao Paulo, Brasil
  • José Vicente Valarelli Universidade de Sao Paulo, Institute de Geociencias, Caixa Postal 20’899, BR - 01’000 Sao Paulo, Brasil
  • Rudolf Giovanoli Laboratorium für Elektronenmikroskopie, Institut für anorganische, analytische und physikalische Chemie der Universität Bern, Freiestr. 3, Postfach 140, CH-3000 Bern 9, Schweiz
  • Silvania M. Netto Universidade de Sao Paulo, Institute de Geociencias, Caixa Postal 20’899, BR - 01’000 Sao Paulo, Brasil.

DOI:

https://doi.org/10.2533/chimia.1984.427

Abstract

Cryptomelane with a formal composition of K0.88Mn(III)0.24Mn(IV)7.60O16.00∙0.33H2O was precipitated from a solution of sulfuric acid containing dissolved manganese sulfate. The oxidation state of manganese in solution was controlled by bubbling pure oxygen gas through and the pH was raised from 1.00 to 2.90 by addition of KOH.
Measurements of pH and Eh as well as determination of ion activities in equilibrium with the obtained solid led to a pH = f(Eh) curve with an inclination corresponding to the synthesis equation:

(0.88K+) + 7.84Mn2+ + 16.01H2O ⇌ K0.88Mn(III)0.24Mn(IV)7.60O16.00∙0.33H2O + 31.36H+ + 15.68e

By Nernst’s equation an E° value was determined permitting the calculation of Gibbs free energy of reaction, (ΔGR)°298 = 1323.98 ± 3.29 kJ∙mol-1  and formation, ΔG°fCRYP = - 4482.08 ±3.40 kJ∙mol-1 of synthesized cryptomelane.

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Published

1984-12-31

Issue

Vol. 38 No. 12 (1984): Forschung/Research

Section

Kurze Mitteilungen

License

Copyright (c) 1984 Raphael Hypolito

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

How to Cite

[1]
R. Hypólito, J. V. Valarelli, R. Giovanoli, S. M. Netto, Chimia 1984, 38, 427, DOI: 10.2533/chimia.1984.427.