ISSN:
1572-8927
Keywords:
Ion-solvent interaction
;
ion pairs
;
conductance in mixed solvents
;
tetrabutylammonium bromide
;
tetraphenylphosphonium bromide
;
tetraphenylphosphonium chloride
;
tetrapropylammonium bromide
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Conductances at 25.00°C are reported for the following systems: tetrabutylammonium bromide in dimethyl sulfoxide-acetone mixtures (Bu4NBr in Me2SO−Me2CO); tetraphenylphosphonium bromide (Ph4PBr) in water Me2SO, Me2CO, and in the mixtures H2O−Me2SO, Me2SO−Me2CO and Me2CO−H2O; Ph4PCl in Me2SO, Me2CO, H2O−Me2SO, and Me2SO−Me2CO; and tetrapropylammonium bromide (Pr4NBr) in Me2SO and Me2CO. The data were analyzed using the Fuoss 1978 equation which is based on the coupled equilibria: (unpaired ions)⇌(solvent-separated pairs)⇌(contact pairs). The conductimetric pairing constantK A =K R(l+K s) is the product of two factors:K R, which describes the first (diffusion controlled) equilibrium andK s=exp(−E s/kT), which describes the second (system-specific) equilibrium. Ions with overlapping cospheres (of diameterR) are defined as paired: their center-to-center distancer lies in the rangea≤r≤R; contact pairs (r=a) are ions which have one ion of opposite charge as a nearest neighbor, all other nearest and next nearest neighbors being solvent molecules. The quantityE s is the difference in free energy between the states defined byr=R andr=a. For the Me2SO−Me2CO systems,E s is positive for solutions in Me2SO and decreases through zero to negative values as the fraction of the less polarizable acetone increases. For solutions in waterE s is also positive. On addition of Me2SO or Me2CO,E s initially increases, goes through a maximum, and then decreases to negative values as the fraction of the less polarizable component increases. The decrease is an electrostatic effect, common to all the systems. The initial increase inE s appears when the small water molecules surrounding solvent-separated pairs are replaced by organic molecules which have greater volumes than water.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00715996
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