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The effects of chloride salts of some cations on the molecular organization of H2O. Towards understanding the Hofmeister series. II

TitleThe effects of chloride salts of some cations on the molecular organization of H2O. Towards understanding the Hofmeister series. II
Publication TypeJournal Article
Year of Publication2006
AuthorsKoga, Y, Katayanagi, H, Davies, JV, Kato, H, Nishikawa, K, Westh, P
JournalBulletin of the Chemical Society of Japan
Volume79
Pagination1347-1354
Date PublishedSep
Type of ArticleArticle
ISBN Number0009-2673
KeywordsAQUEOUS-SOLUTIONS, EXCESS CHEMICAL-POTENTIALS, HEAT-CAPACITIES, INTERMOLECULAR INTERACTIONS, MIXING SCHEMES, PARTIAL MOLAR ENTHALPIES, TETRAALKYLAMMONIUM HALIDES, TETRAMETHYL UREA, THERMODYNAMIC APPROACH, WATER MIXTURES
Abstract

We use the thermodynamic behaviour of I-propanol (1P) as a probe in ternary 1P-salt-H2O systems to elucidate the effect of a salt on the molecular organization of H2O. For salts, we have chosen CaCl2, NH4Cl, and (CH3)(4)NCl (TMAC). Having fixed the counter anion at Cl-, we compare here mainly the effects of chosen cations on H2O. Together with an earlier study on NaCl, we found that Ca2+, Na+, and NH4+ are hydrated by a number of H2O molecules and leave the bulk H2O away from the hydration shell unperturbed. The hydration numbers were found to be 6.4 +/- 1.6, and 1.2 +/- 0.4, for Ca2+ and NH4+, respectively with the hydration number 5.2 for Na+, the result of a simulation study, chosen as a reference. Thus, a salting out (also referred to as structure making, stabilizing, or kosmotropic) tendency would decrease in the order; Ca2+ > Na+ > NH4+. TMA(+), on the other hand, showed a more hydrophilic characteristics than the probing 1P. Thus, TMA(+) is rather chaotropic (salting in, structure breaking or destabilizing) within this methodology.

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