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Molar volumes and heat capacities of electrolytes and ions in N,N-dimethylformamide

Płaczek, A., Grzybkowski, W. and Hefter, G. (2008) Molar volumes and heat capacities of electrolytes and ions in N,N-dimethylformamide. Journal of Physical Chemistry B, 112 (39). pp. 12366-12373.

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Densities and heat capacities of various 1:1 and higher-charged electrolytes have been measured in N,N-dimethylformamide (DMF) at 25 °C using a series-connected flow densimeter and Picker calorimeter. Standard molar volumes Vo and isobaric heat capacities Cpo derived from these data were split into their ionic contributions using the tetraphenylphosphonium tetraphenylborate (TPTB) reference electrolyte assumption. The values so obtained have enabled a meaningful separation of the effects of cationic size and charge for the first time in a nonaqueous solvent. As in water, Vo(Mn+) values in DMF are markedly more negative for higher-charged cations due to increasing electrostriction of the solvent. In contrast, ionic charge has a much smaller effect on C po(Mn+) in DMF than in water. Ionic volumes in DMF show the expected dependence on size but those of small monatomic monovalent cations and anions imply a significant difference in accessibility of the electron donor and acceptor sites on the DMF molecule. Ionic heat capacities in DMF show a relatively weak dependence on ionic size that, when corrected for charge, is opposite to that in water. Both Vo(R4N +) and Cpo(R4N+) in DMF show the usual linear dependence on carbon number but differ from their values in aqueous solution due to the absence of hydrophobic interactions in DMF

Item Type: Journal Article
Murdoch Affiliation(s): School of Chemical and Mathematical Science
Publisher: American Chemical Society
Copyright: © 2008 American Chemical Society.
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