Handbook of Solvents - George Wypych - ChemTech - Ventech!

9.3 Physical properties of mixed solvents 517
Two basic factors which influence conductivity of binary solvent mixture are viscosity
and permittivity. The influence of these factors on specific conductivity is quantitatively
considered in empirical equation:
[ 1 1 ( 1)
]
κ = 1/ ηexp ln κ η −L 1/ ε−1/ ε
[9.38]
where:
κ conductivity (symbols without index belong to the mixture properties, index 1 belongs to
electrolyte component)
L = aεε 1 2/( ε1−ε2) a proportionality coefficient
and in non-empirically equation:
where:
( )
ln κ = const + 1/ ε const + const + const + 1/ 2 lnc −lnη
[9.39]
1 2 3 4
c concentration, mol l -1
consts calculated from the equations 11 based on crystallographic radii of the ions, dipole
moments of molecules of mixed solution, and ε of mixture components
From equations [9.38] and [9.39], it follows that isotherms of the logarithm of conductivity
corrected for viscosity and concentration lnκηc -1/2 have to be a linear function of reciprocal
ε. Validity of this assumption is confirmed in Figure 9.1. Control of properties of
multi-component mixture of solvents is achieved by methods of optimization based on analytical
dependencies of their properties in composition:
( i )
( )
I I I
II II II
y = f y , y , �c , c , �c , y = f y , y , �c , c �c
1 2 1 2 −1 1 2 1 2 i −1
[9.40]
where:
y I ,y II
any property of solvent
I II
y1, y 2 initial property of solvent
Concentration dependencies of permittivity, viscosity, density (molar volume) and
conductivity described here permit to select with certainty the composition of mixed solvent,
characterized by any value of mentioned properties.
9.3.2 PHYSICAL CHARACTERISTICS
OF THE MIXED SOLVENTS WITH
CHEMICAL INTERACTION
BETWEEN COMPONENTS
In this section, we discuss physical characteristic
change due to the changes of binary
mixed solvent composition in the systems
with chemical interactions between components
(these systems are the most commonly
used in science and technology). Comprehensive
discussion of the physical and chemical
analysis of such systems, including
Figure 9.1. Dependencies lnκηc stoichiometry and stability constants, determination
of the formation of heteromolecular
-1/2 on 1/ε at 393.15K
for systems containing tetrabutylammoniumbromide
and aprotic solvent (1-nitromethane, 2-acetonitrile,
3-pyridine, 4-chlorobenzene, 5-benzene).