Abstract:
The densities, viscosities and relative viscosities of solutions of several
univalent electrolytes Lithium bromide (LiBr), Sodium bromide (NaBr),
Potassium bromide (KBr), Rubidium bromide (RbBr) Cesium bromide (CsBr)
and reference salts tetra butyl ammonium tetra phenyl borate (BU4NBPh4 ),
tetra butyl ammonium bromide (BU4NBr) and potassium chloride (KCl)
were measured over the entire range of concentration at 25 oC to 45oC in pure
DMSO, pure water and DMSO- H2O binary mixtures.
Data was analysed by Jones-Dole equation to determine ion –ion
interactions (the A- coefficients), ion- solvent interaction, (the B- coefficients)
for alkali metal bromides in pure DMSO, pure water and DMSO- H2O binary
mixtures. The values of A- coefficients were small and almost positive in all
the cases. The values of B- coefficients were large and almost positive of all
the salts in DMSO and DMSO- H2O mixtures, which showed the structure
making abilities of the salts in DMSO- H2O mixtures at all the five
temperatures.
The values of viscosity B- coefficients were found negative for KBr, RbBr and
CsBr in pure water at all the five temperatures, which showed the structure
breaking abilities of the salts while the values of viscosity B- coefficients of
LiBr and NaBr in water at all the five temperatures were found positive and
behave as structure makers.
iv
The viscosity B- coefficient data was further splitted into ionic B-
coefficient for non-aqueous solvents by using Gill and Sharma’s convention
and Gurney’s convention into ionic B- coefficients for aqueous solvent
systems.
From ionic B- coefficient data it was observed that in pure DMSO all
the alkali metals have strong structure making abilities. It was also observed
that these structure making abilities were decreased with the increase in ionic
radii or temperature. While in aqueous solvents (DMSO- H2O) mixtures the
structure forming capabilities were weakened and structure breaking abilities
were appeared at all temperatures.
In pure water except Li+ and Na+ all the ions showed the structure
breaking properties, which increased with the increase in temperature. The
data obtained during this study was found in good agreement with those
values which were already available in literature.
The Transition state parameters such as free energies and energies of
activation for viscous flow have been calculated for the whole solvent system.
From the present study it is concluded that the energy of activation of viscous
flow is influenced by the concentration and the size of the solute particles. So
the energy of activation of viscous flow for CsBr is greater than for RbBr,
KBr, NaBr and LiBr in DMSO and DMSO-H2O mixtures.
It is also observed that the energy of activation of viscous flow are
greater for alkali metal bromides in water than in DMSO due to the presence
of a network of hydrogen bonds in water. For the free energy of activation for
viscous flow, it is observed that the free energy of activation for viscous flow
increases with temperature.