Molar volumes and heat capacities of electrolytes and ions in N,N-dimethylformamide.
J Phys Chem B
; 112(39): 12366-73, 2008 Oct 02.
Article
em En
| MEDLINE
| ID: mdl-18783193
ABSTRACT
Densities and heat capacities of various 11 and higher-charged electrolytes have been measured in N,N-dimethylformamide (DMF) at 25 degrees C using a series-connected flow densimeter and Picker calorimeter. Standard molar volumes V (o) and isobaric heat capacities C p (o) 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, V (o)(M (n+) ) 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 p (o)(M (n+) ) 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 V (o)(R 4N (+)) and C p (o)(R 4N (+)) 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.
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MEDLINE
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En
Ano de publicação:
2008
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Article