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Solvation numbers and hydration constant for thorium(IV) in ethanol-water medium

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Abstract

The solvation number and hydration constant of Th4+ in ethanol-water medium were determined at 25°C using UV-spectral and electrochemical measurements. A solvate formation equilibrium is demonstrated and characterized. Three molecules of ethanol (S) can bond to the metal cation with strengths comparable to that for H2O to form ThS3(H2O) 4+3 Formation of thorium monochelate with lawsone (2-hydroxy-1,4-naphthoquinone) eliminates bonding with alcohol molecules. The dissociation constant of the chelating agentsKa and the formation contant of the monochelated metal ionsK *f that are essentially independent of the solution composition are evaluated. Hydration titrations involving thorium-lawsone monochelate are performed and the data obtained from the changes of pH with solvent composition are analyzed. The solution independent constant,sK *f for thorium-lawsone complex formation in mixed aqueous ethanol is given by

$$log_s K_f * = vpK_a + log_s K_h - log[LH] - vpH + 3logv$$

where vpKa is the dissociation constant of the chelating agent LH in the solvent system of ν volume fraction of water andsKh is the solution-independent hydration constant of thorium (IV) in the solvent system. Log-values for the constantssKh,sK *f andsK *a are found to be 7.8±0.02, 11.38±0.04 and −0.753, respectively.

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Authors and Affiliations

  1. Department of Chemistry, Faculty of Science, Assiut University, Assiut, Egypt

    Hassan Sedaira, Kamal A. Idriss, Elham Y. Hashem, Mohamed M. Seleim & Abu-Bakr El-Nady

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  1. Hassan Sedaira
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  2. Kamal A. Idriss
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  3. Elham Y. Hashem
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  4. Mohamed M. Seleim
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  5. Abu-Bakr El-Nady
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Sedaira, H., Idriss, K.A., Hashem, E.Y. et al. Solvation numbers and hydration constant for thorium(IV) in ethanol-water medium. J Solution Chem 25, 95–103 (1996). https://doi.org/10.1007/BF00972762

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  • DOI: https://doi.org/10.1007/BF00972762

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