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CH PTER I
INTRODUCTION ND REVIEW OF LITER TURE
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CH PTER I
INTRODUCTION ND REVIEW OF LITER TURE
1 1INTRODUCTION
The study of propagation of ultrasonic waves in liquid systems and solids is now well
established as an effective means of examining certain physical properties of the materials.
It is particularly well adapted to examining changes in such physical properties at the macro
level. The data obtained from ultrasonic propagation parameters
in
liquid mixtures and
solutions viz., ultrasonic velocity and attenuation, and their variation wit concentration of
one of the
components, helps to understand the nature of molecular interactions in the
mixtures. Ow ing to high sensitivity to very low population densities at high energy states,
ultrasonic methods have been preferred, and are reported to be complementary to the
other techniques Wyn et al., 1966) like dielectric relaxation, infrared spectroscopy, nuclear
magnetic resonance, etc. Ultrasonic studies are also extensively used in the con finnation al
analysis of organic molecules Bergelson, 1960). Several empirical and semi-em pirical
formulae have been developed correlating velocity and attenuation with other molecular
parameters, and a brief account of theoretical aspects are given below.
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1 2
THEORETICAL ASPECTS
1 2 1 THEORY OF SOUND PROPAGATION
Propagation of sound waves in a medium may be treated as a series of compressions
and rarefactions travelling along the direction of propagation so that the molecular planes of
the medium are displaced from their mean position. TIe displacement
5)
and velocity C) of
the waves are related by the wave equation,
I t is assumed here that the compressions and rarefactions are both reversible
and adiabatic. The wave equation may be rewritten using the isentropic
compressibility
P,)
and density p) of the medium as,
comparing equations 1 .I ) and I .2 it is evident that
c (p,p)-
1 . 3 )
Thus in the limit of the above assumptions the velocity of the sound waves depends
only on
P
and
p
Jack Blitz, 1963).
1 2 2 HYDRATION NUMBER
In the case of aqueous solutions of electrolytes, the major effect of ion-solvent
interaction is the phenomenon of hydration, and it involves the attachment of certain number
of water mulecules to the positive and negative ions. The first layer of firmly bound water
2
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molecules to the ions are almost incompressible, and they contribute towards the primary
hydration of the ion. The second water layer beyond the primary hydration sheath, on which
also the ion has some orientation effect, is the secondary hydration. It is shown that the
molecules of water which form the secondary hydration shells are compressed to the
maximum extent possible due to the intense electric fields around the ions. The external
pressure compressed the remainder of the solvent water molecules (Kerestov et
al.
1980).
Primary hydration number can be computed from entropies, apparent molal volume, and from
mobility. They can also be computed from compressibility nlethod which is associated with
ultrasonic velocity
A
solution of volume V containing of total number of
n
moles of water, of which h
moles are attached to ions as hydrated molecules. If n moles of ions are solvated. and P
and P are the compressibilities of solvent and solution respectively, then for dilute
solutions the hydration number (h) is given by
The hydration number of a solu te in aqueous solution can be determined using the
above relation, where the compressibilities of the solvent and solution are determined
ultrasonically (Robinson et al., 1959; Bockris et al., 1970).
1 2 3 JACOBSON S
FREE LENGTH THEORY
Kittel (1946), has applied Tonk s equation of state to wave propagation in liquids .
The molar volume V is divided into two parts. one part V which is the volume of
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geometric closest packing of molecules, and the second part is available volume V,=(V-V,).
The Tonk s equation of state for liquid is given by
PV, =
3R,T
where R, is the universal gas constant.
The velocity of ultrasonic waves in a liquid is given by the relation
CZ
=
g)
(1.6)
where
SP
is the change in pressure due to the sound wave, and
Sp
is the corresponding
change in density of the medium under adiabatic conditions.
Using equations (1.5) and
(1.6) Kinel showed that the ultrasonic velocity (C) in a liquid is given by
where y,,, is the ratio of specific heat at constant pressure to constant volum e. Equation (1.7)
indicates a linear relation between V, and V
Jacobson (1951) suggested that the adiabatic compressibility of a liquid can be
understood in terms of the intermolecular free length which is the distance between the
surfaces of the molecules, hereafter designated as
L .
L is related to the available volume V,
and the surface area per molecule Y through the relation of Eyring (1937) as
L,=
+
(1.8)
where Y is equal to
36n.v;)
N is Aragadm i number and
o
s the volume at absolute
zero). The intermolecular free length depends on the type of packing, and the extent of
association in a given liquid.
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1 2 4 THEORY OF INTERNAL PRESSURE
Richards (1925), Hildebrand (1950), and van der Waals (1873) suggested the
importance of internal pressure P, which indicates the strength of attractive forces between the
molecules. The term
aW
in van der Waals equation being the measure of the attractive
forces of the molecules is called the cohesive or internal pressure. and is of very great
importance in the study of the properties of liquids.
Intermolecular forces give a liquid its cohesion.
The attractive forces mainly
comprises of hydrogen bonding, dipole-dipole interaction, multipolar, and dispersion
interactions. Repulsive forces acting over very small intermolecular distances play a minor
role in the cohes ion process under normal circumstances. Cohesion creates a pressure of 10'
to lo4atmospheres within the liquid. Dissolved solutes experience some of this pressure, and
the amount of internal pressure increases whenever they interact with solvent through
hydrogen bonding, charge transfer, Coulombic or van der Waals interaction. Thus a solu te is
subjected to a Structural pressure from the solvent and a Chemical pressure from the
interaction with the solvent, and hence the solution exists under a higher internal pressure
than the pure solvent.
A liquid undergoing a small isothermal-volume expansion does work against the
cohesive forces which cause a change in the internal energy
(U).
The function
(6U/6V),
is
known as the internal pressure
(P,).
From Maxwell's equation of thermodynamics
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Moelwyn-Hughes, 1964), it follows that
i.e., Internal pressure =Kinetic pressure - External pressure.
The term SPIST),
in
the equation is called the thermal pressure coefficient, and
it is equal to
lp
where is the coefficient of thermal expansion, and p is the isothermal
compressibility. As a l p has a large value, and as such
P
can be neglected in comparison to
SPIST),. Hence the equation reduces to
since p p,, this equation also can be expressed
s
ro
UP
where is the ratio of specific heat at constant pressure to constant volume
Extensive study of literature shows that the internal pressure in liquid solution
seems to be such single factor which varies due to all the interactions o f type 1-1, 2-2, and 1-2
where 1 and 2 are constituents of mixtures Srinivasan, 1978). It is also known that many
properties of ionic solution may be derived in terms of intermolecular forces without
appealing to the concepts of electrical charge or ionic radii
1 2 5 EXCESS COMPRESSIBILITY
The compressibility for the
ideal liquid n~ixtures is an additive h c t i o n of
compressibilities of the components for most
of the liquid mixtures. It ise stim ated , for
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pwe liquids and those of the mixture, the excess intermolecular free length L can be thus
computed.
f L L;x~L / B X ~
1.16)
where
Lk
and
L
are the intermolecular free length,
X
and
X
are mole fractions of the
components A and B, and L F i s he experimental intermolecular free length of the mixture.
1.2.8 RELATIVE ASSOCIATION
Relative association is a parameter used to assess the association in any solution
relative to the association existing in water at
0C.
t is estimated using the following
relation.
.A
)' 1.16a)
where
p
and C are the density and ultrasonic velocity of the solution at any temperature, and
p and C, are density and ultrasonic velocity o f water at OC Satyanarayana Murthy, 1964).
1.3
THEORY OF ULTRASONIC ABSORPTION
When a plane progressive wave passes through a system, each small volume in the
system is subjected to a time dependent perturbation. The study of ul tm on ic absorpt ion is to
understand how the system responds to the perturbation, and relaxes in fluid media are
attributed mainly due to the following causes.
1.3.1 CLASSICAL ABSORPTION
The propagation of ultrasonic wave through a thin layer of medium suffers a
fractional loss of energy. If I and
1
are the intens~tie s f the sound before and after passing
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through a layer of thickness X, then
= o e - 2 0 ~ X 1 . 1 7 )
where
a,
is defined as the absorption coefficient of the medium, and is generally expressed in
Nepersicentimetre. The classical absorption arises because the propagating wave loses
energy in overcoming the shear viscosity q,) and thermal conductivity (K) of liquids. It may
be represented as
al),iarr = aA)*hear aA),hrrmo
It is winen as follows in the form of Stoke's-Kirchoff equation,
where p is the density of the medium, C is the ultrasonic velocity in the medium,
y
is the
ratio of specific heats, and
C,
the specific heat at constant volume.
As the thermal conductivity of most of the liquids is generally small, its
contribution to the attenuation of ultrasonic waves is negligible -10 2P p cm s' ) except for
liquid metals. However, the attenuation due to shear viscosity will have a significant
contribution (-10 ' Np cm s'
).
1 3 2 EXCESS ABSORPTION
The classical absorption may be calculated theoretically using the relation
I l 9 )
as
a sum of shear viscosity and thermal conductivity contributions. But in many liquids, the
experimentally measured ultrasonic absorption i s found to be higher than the classical
I0
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absorption. The difference between these two absorptions is termed a s excess absorption
a/f3x.
1 3 3 MOLECULAR ABSORPTION
For most of the liquids, the experimentally measured absorption is higher than the
classical absorption. This excess absorption is due to molecular relaxation. The molecular
relaxation arises due to either thermal relaxation or structural relaxation or both.
1 3 4 THERMA L RELAXATION
During adiabatic compression of a unit volume of the system by ultrasonic sound
waves, the total energy is made up of many different contributions such as translational.
vibrational, rotational. and intermolecular structural) energies. The translational energy
derived from the acoustic wave is passed from one molecule to another without delay.
A
part of this energy may be converted into rotational or vibrational energy during collision.
The equilibrium between the three energy states is gradually restored. This transfer of
energy from external to internal degrees of freedom requires finite time, and the medium is
said to be relaxing. This phenomenon is termed as thermal relaxation which causes the
attenuation of sound waves. Rotational isomerism and vibrational relaxation
are
the most
commonly observed types of thermal relaxation.
11 3 5
STRUCTURAL RELAXATION
This type of relaxation was first proposed by Hall
1948)
to explain the excess
absorption in water, which could not be explained on the basis of thermal relaxation alone.
Structural relaxation occurs in liquids like water, alcohol, and similar polymeric liquids
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considered that (1) and (2) were states of equilibrium separated by a potential barrier of AF,
and obtained an expression for the relaxation time
as
given below
where 7, is the shear viscosity, V molar volume of liquid, is the gas constant, is the
absolute temperature, and K is Boltzmann's constant.
1 3 6
VOLUME VISCOSITY
In order to explain the excess absorption in some liquids, volume viscosity was
introduced in addition to shear viscosity. One of the approaches adopted to explain the
volume viscosity is a pseudo-lattice description of the liquid state (Herzfeld et al.,
1959).
In
this model, molecules jump from lattice positions to the holes (vacant lattice sites) , and the
holes jump to the neighbouring lattice sites. The presence of such holes account for the fact
the molar volume of the liquid is nearly aleays greater than the molar volume of the
corresponding sol id. When a liquid is subjected to a shearing force, molecules jump between
neighbouring planes perpendicular to the direction of shear. When a liquid is compressed, the
molecules jump to occupy holes resulting in closer packing i.e., the holes move out on
compression. This leads to a volume viscosity 7 . The relaxation of volume viscosity (q,)
and shear viscosity (7,) with the increase in frequency results from a kinetic control of
molecular reorganization. However, the volume viscosity cannot be independently
determined. It is established from the ultrasonic absorption in the liquid by the folloaing
relation:
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In order to explain the ultrasonic absorption in water, Hall
(1948)
used the model of
water developed by Bemal and Fowler (1933). According to these authors, the water exists
in two phases, in which one phase is dense monomeric water and the other ice-like structure.
When the ultrasonic waves pass through water, the equilibrium between these two phases is
disturbed, and causes the absorption of ultrasonic waves. Hall developed an expression
based on the above model for the excess ultrasonic absorption as
f )
2n2pcp.r
(1.23)
where s is the structural relaxation time. e is the relaxational part of compressibility. C the
ultrasonic velocity and
p
the density of the liquid.
The structural relaxation time
is related to the molar volume, and free energy
d; rence between the two states is given by the equation (1.21).
The relaxational part of compressibility (P,) was related to the volume viscosity, and
the relaxation time
by
an expression developed
by
Litovitz and Davis (1965)
s
r ~
l v = x
(1.24)
where p is the static compressibility.
For the viscoelastic liquids it has been found that the relaxational time (s ) may be
related to the static compressibility Po
),
and the two viscosities q, and q , as follows
~ ~ ( q .4q1)
(1.25)
1 4 HYDROGEN BONDING
According to Pimental et al. (1959), a hydrogen bond exists when a hydrogen atom is
bonded tc two or more other atoms . Usually the hydrogen bond refers to the enti re group of
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three or more atoms, which are involved in a configuration X-H-Y, where X and Y may be
like or unlike atom s. One of the two bonds X-H or H-Y may be stronger than the other. The
weaker of the two bonds is some times called as hydrogen bond to distinguish it fiom the
stronger bond which may be a covalent bond. Such a bonding situation is often indicated by
X-H ..Y . Although the hydrogen bond is not a strong bond, its bond energy, that is, the
energy of the reaction XH+Y+X HY lying in most cases in the range to lOKCal/mole.
Hydrogen bonding is found with strong electronegative atoms like
F,
0 N, CI, etc The
atom X o r Y is one of these electronegative a toms in the configuration X-H-Y. Increasing the
electronegativity o f an atom increases its power of forming hydrogen bonds. In almost all
hydrogen bonds the hydrogen atom nearer to one of the two adjacent electronegative atoms
than to the other. These hydrogen bonds, existing in substances containing 0- H , h -H,
F-H
groups, provide special properties to these substances.
The hydrogen bond species varied from the highly symmetric ones like F-H ,.F to
general form of A-H.,B type. The variation of ultrasonic velocity data in liquid mixtures or
solid liquid solutions gives a clue to the intermolecular association through hydrogen bonding
(Anbananthan, 1979; Tabhane et al., 1983; Nambinarayanan et al., 1989) where such
possibility exists.
1.4.1 INFRARED
SPE TROS OPY
lnfrared absorption spectrophotometry has proved to be a valuable technique for
identification and characterisation of organic substances,
Infrared spectra are directly
involved with the vibration of atoms, or groups of atoms in a molecule, and arise from
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transition between the vibrational energy levels of the molecules. Stretching and bending are
the two kinds of fundamental vibrations for molecules. If the periodic oscillation is
moderate, the system follows Hooke's law to first approximation, and the frequency of
stretching (v) vibration can be expressed as
where k is the force constant of the bond, and M is the reduced mass of the system. The
various stretching and bending vibration of a bond occur at certain quantised frequencies.
When infrared light of that same frequency is incident on the molecule, energy is absorbed,
and the amplitude of vibration is increased. non-linear molecule that contains toms has
(3N-6) possible fundamental vibrational modes that can be responsible for the absorption in
the infrared. For a particular vibration to result in the absorption of energy, that vibration
must cause a change in the dipole moment
of
the molecule. A number of characteristic group
absorption frequencies for several structural types are compiled. This compilation is
particularly useful when the spectrum of
an
unknown material has been obtained. For
example, a stretching vibration of the
0 H
ond is at 3600 cm , but is lowered to 2630 cm-'
in the 0 - D bond. For P=O , a strong band appears in the range 1100 to 1300 cm .
Appearance of a band suggests the presence of a functional group, but it has to be conf irmed
by further analysis. However, if the spectrum does not contain an absorption typical of a
certain functional group, the molecule does not contain that functional group.
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the solvent and the mixture have been estimated using Flory s theo ry.
These excess
parameters are proportional to the strength of the interaction between unlike molecules in a
mixture.
Ultrasonic absorption studies have made a significant contribution to chemical
physics and its various aspects have been reviewed by Herzfeld (1959) and Blandamer
(1973). As the present thesis deals with ultrasonic velocity and absorption studies pertaining
to binary liquid mixtures of organic liquids, carboxylic acids, electrolytes, and amino acids, a
brief review of the relevant literature is given below.
1 5 1
LIQUIDS AND LIQUID
MIXTUR S
Kaulgud (1963) measured ultrasonic velocity and adiabatic compressibilities of
binary mixtures of acetonitrile and nitromethane in benzene and carbon tetrachloride. He also
measured the ultrasonic velocity in the mixtures of acetone-carbon tetrachloride, at different
concentrations. It is generally observed that the adiabatic compressibility decreases as the
ultrasonic velocity increases. A peculiar behaviour was observed in the mixtures of acetone
and acetonitrile in carbon tetrachloride when both ultrasonic velocity and adiabatic
compressibility decrease with increase in the concentration of acetone and acetonitrile. These
peculiarities have been explained on the basis of thermodynamical excess functions and also
the variation of intermolecular free length after mixing.
The densities and ultrasonic velocities have been measured by Singh et al. (1977) at a
temperature of 30C in ternary liquid mixtures of acetonitrile-carbon tetrachloride-n-butanol;
dioxane-cyclohexane-chloroform. The increase in free length in the solutions due to the
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mixing results in lowering of the velocity. From the study it was concluded that the free
length was a predominant factor in determining the nature of variation of sound velocity in
these mixtures. The changes from positive to increasingly negative excess molar volumes
have been interpreted in terms of closer approach of unlike molecules leading to reduction in
compressibility. It has been further concluded that the dispersion forces make a positive
contribution to these values, while the dipole-dipole and hydrogen bonding forces between
unlike components make a negative contribution.
Ultrasonic velocities and adiabatic com pressibilit~es in binary ~ lq u id mixtures of
ani line phenol, quinoline phenol and pyridine phenol have been studied by Adgaonkar
et al. 197 7). It is observed that at the molar ratio 1:1, the velocity and compressibility
showed discontinuity. These discontinuities have been attributed to complex formation
through hydrogen bonding. Complex formation in these mixtures has been explained on the
basis of spherical-cage model, where decrease in adiabatic compressibility indicates a
decrease in free volume at the discontinuities.
The ultrasonic velocity and adiabatic compressibility measurement at room
temperature in binary mixtures of aniline o-cresol, phenoline o-cresol and pyridine
o-cresol have been used by Adgaonkar et al. 1979) to study the physical propert~ es f these
mixtures. The complex formation through hydrogen bonding for
the
above liquid mixtures
have been observed. From these studies, it was inferred that the com plex formation w s
stronger in the case of pyridine o-cresol mixture and weaker in others.
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The ultrasonic velocity in liquid mixtures of dioxane with homologous series of
alcohols have been carried out by Anbananthan 1979) with a view to studying the
molecular association in these mixtures. The plots of ultrasonic velocity and adiabatic
compressibility versus composition of the mixtures have shown maximum in velocity and
minimum in compressibility. The minimum in compressibility in these mixtures indicates
complex formation through hydrogen bonding.
Excess volumes and isentropic compressibilities in the mixtures of acetonitrile in
n-propanol, i-propanol, n-butanol, i-butanol, and cyclohexanol were determined at 300K by
Narayanasamy et al. 1981). It is reported that these mixtures show positive excess volumes,
and these excess volumes are attributed to weak hydrogen bonding.
Intermolecular free length L between the molecules in the binary liquid
mixtures of carbon tetrachloride
benzene, carbon tetrachloride toluene, carbon
tetrachloride methanol, methanol water, and ethanol water were calculated by
Suryanarayana et al. 1982) in the complete concentration range as a function of temperature
from 282K to 343K using the various formulae in vogue. It was concluded that L,
calculated in each case from the corresponding adiabatic compressibility was simple, direct,
and sufficiently accurate.
The ultrasonic study by Dharmaraju et al . 1983) in the mixtures of acentonitrile with
n-pentanol, n-heptanol, n-octanol at 303K shows a weak interaction. The physical parameters
like excess volume and excess compressibility increase with the chain length of alcohols.
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The ultrasonic studies on the nature of molecular interactions in the mixtures of
carbon tetrachloride o-toluidine and carbon tetrachloride p-toluidine were reported by
Tabhane et al. 1983). The ultrasonic studies on the nature of compressibility is negative and
increases in magnitude up to about 1 I molar concentration and decreases thereafter. The
maximum in excess compressibility in this mixture indicated complex formation through
hydrogen bonding.
Ultrasonic velocity of solutions of triphenyltin chloride in acetone was measured at
30,
3 5
40, and 45C by Srivastava et al. 1983) using single crystal interferometer at a
frequency of 2
MHz.
Various parameters were calculated, and the results were interpreted in
the light of solute-solvent interactions.
An ultimate study on ion-solvent interaction in the solutions of tetra alkylamrnonium
iodides bN 1; where
R
C, to n-C,) in dimethyl sulphoxide has been carried out by Pankaj
and Sharm a 1991) at 40, 50, and 60C. The study reveals that the
N'
cation remains more
or less excluded in this solvent as found in other non-aqueous solvents like sulpholane and
ethylene carbonates.
The excess molar volumes V h f mixtures of water polyethylene glycol mono-,
di-, tri-, and tetra- ethylene glycols) were measured as a function of compositions at 303.15
and 308.1 5K. The values of
VE
were all negative over the entire composition range. Apparent
molar volumes have been calculated from these data. These results suggested that weak
hydrophobic effects might develop in the water-rich region, its magnitude increased with the
size of the hydrocarbon chain Pal et al., 1994
).
1
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Srivastava et al. (1986) have evaluated excess internal pressure in the binary liquid
mixtures of water t-butanol, water n-propanol, water ethylene glycol, and water
glycerol at 25 C. The ultrasonic velocity and density were taken from the literature. It was
reported that intermolecular interaction in the case of water monohydric alcohols was
stronger than that of water polyhydric alcohols. When monohydric alcohols were mixed
with water, hydrogen bonding between like molecules was broken down and hydrogen bonds
were formed between unlike molecules. In the case of polyhydric alcohols, mutual
association between their molecules was stronger than with water molecules so that the
strength of interactions decreased in these systems
Chauhan et al. (1994) measured ultrasonic velocity, density, and viscosity of binary
mixtures of acetonitrile (AN) and propylene carbonate (PC) between 25 and 45 C. Adiabatic
compressibility, excess adiabatic compressibility, excess viscosity, and excess volume were
calculated. The activation energies for viscous flow for AN and PC interpreted by the
activated rate process revealed relatively stronger molecular association in PC. Excess
functions while examined as a function of mole fraction of PC were found to be negative
over the whole composition range of AN-PC mixtures between 25 and 4SC. This has
been taken into account for the strong dipole-dipole interactions in AN-PC mixtures.
Ultrasonic speed, isentropic compressibility, dielectric constant, refractive index, and
viscosity data of binary mixtures of quinoline with benzene, toluene, o-xylene or p-xylene
have been experimentally obtained over the whole composition range at 303.15K and the
interactions existing between the components have been discussed by Kalra et al. (1994).
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These studies suggested strong complexation between the molecules of quinoline and
aromatic hydrocarbons.
From the experimentally measured velocity, density, and viscosity data, excess
adiabatic compressibilities, excess volumes, excess internal pressures, etc., in binary liquid
mixtures of ethylacetate and n-butanol have been computed at three temperatures 303.15,
313.1 5, and 323 .15K . AB interactions were found to be predominant in the binary mixtures at
all temperatures besides interstitial site occupation Padmasree et a]., 1994)
Ultrasonic velocities, densities, and viscosities were measured in the three binary
mixtures of acetophenone, 4-chloro acetophenone and 2-hydroxy acetophenone with
isopropanol as the common component by Yanadireddy et al. 1994). Adiabatic
compressibilities and the excess thermodynamic parameters like
BE
VE,
nE
tc., were
computed and the results were discussed in the light of interlintra molecular interactions. In
all the three binary systems,
AB
interactions have been observed to be predominant
besides interstitial site occupation.
The ultrasonic velocity, viscosity, and density of binary mixtures of the extractant
acetylacetone with isoamyl alcohol, benzene, and carbon tetrachloride have been measured by
Rout et al. 1994). over the entire composition of the mixtures at 30, 35. 40, and 45C. The
excess isentropic compressibility, excess intermolecular free length, excess acoustic
impedance, and excess viscosity were calculated from the experimental data. These excess
values for various mixtures tndicated the existence of specific ~nteraction f acetylacetone
with benzene and carbon tetrachloride. The higher positive values of
t
and rlE and less
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negative values of P Land L fof acetylacetone and carbon tetrachloride mixture suggested
that a strong molecular interaction was likely to operate between the unlike molecules.
Sharma et al. (1994) has measured molar excess volume
VE
and molar excess
enthalpies
HE
for methylene bromide nitrobenzene mixture at
308 15K
raph-theoretical
analysis of VE data suggested that while nitrobenzene existed as equilibrium mixture of
monomer and dimer in this mixture, the mixture as such contains a
1: l
molecular complex.
IR and NMR studies lent funher credence to this view point.
1.5.2 CARBOXYLIC ACIDS
Ultrasonic velocity studies have been extended to mixtures of carboxylic acids in
organic liquids. and several interesting results have been reported.
The ultrasonic velocity and adiabatic compressibility and molar sound velocity data
with varying acid concentrations, in mixtures of acetic acid, propionic acid, and butyric acid
separately in solvents like benzene, carbon tetrachloride, chlorofom, pyridine, and acetone
have been studied (Rao, 1965). Both velocity and adiabatic compressibility vary with
concentrations nonlinearly, which is different from that expected for ideal liquid mixtures
thus indicating association between the molecules of carboxylic acids and organic liquids.
The deviation from ideality has been found to be greater in mixtures of carboxylic acids in
solvents of high dipole moment. Plots of squares of free length against adiabatic
compressibility in some of these mixtures have shown nonlinearity and this is in
disag reement with Jacobson s relation
due to structural changes in these mixtures. This
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deviation from linearity is found only in a few systems, and in most of the binary mixtures
the variation is linear.
Nana Rao et al. (1972) have studied the temperature variation of ultrasonic velocity in
ethyl esters of some carboxylic acids in the temperature range of 30C to 80C. In all these
systems, the ultrasonic velocity decreased with increase of temperature and adiabatic
compressibility increased with increase of temperature. Molar sound velocity and molar
compressibility found to be fairly constant, and L a g e m m s relation
s)
oes not
seem to hold good for these liquids.
Subramanyam et al. (1978) have measured the ultrasonic velocities and temperature
coefficient of velocity of dicarboxylic acids, and using Jacobson s free length theory,
association has been estimated. It is found that the association decreases with the increase of
molecular weight of the acid. When association is taken into account, Lagemann s rule which
relates the temperature coefficient of velocity to molecular weight is found to be valid in
these acids . The value of space filling factor rf is found to decrease with the increase of
molecular weight of dicarboxylic acids. The de cr ea e of space filling factor indicates
scope for more compression, and this leads to a decrease in ultrasonic velocity in higher
mem bers of dicarboxylic acid series.
Th e applicability of the Schaaffs collision factor theory and Jacobson s free length
theory to the homologous series of pure mono carboxylic acids and dicarboxylic acids in
liquid state has been tested by Ragupathy Rao et al. (1979) using ultrasonic studies. It has
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been observed that the compressibility of mono carboxylic acids is greater than that of
dicarboxylic acids.
Ultrasonic absorption has been measured in p-dioxanelwater system by Atkinson et al.
(1980) at 25 and l lC at nine concentrations over the frequency range 0.3-630 MHz. It is
shown that the frequency dependence can be fitted quantitatively by the fluctuation theory of
Romanov and Solov ev (1965) if NMR determined
difhsion data are available. The
experimentally determined amplitude of absorption agrees very well with that calculated
using experimental thermodynamic data and the R-S theory. The ultrasonic relaxation times
show the same concentration dependence as the high frequency dielectric relaxation
measured by Garg and Smyth. The discussion considers the ultrasonic fluctuations
a
dynamic
analogue of the cla thrate hydrate forming proclivities of such solutes.
The ultrasonic velocity studies in the solution of p- and o-hydroxy benzoic acids in
dioxane and in those of benzoic acids in benzene for several low concentrations have been
measured by Anbananthan et al. (1975) . It has been reported that there is a formation of
intermolecular hydrogen bonds between p and o-hydroxybenzoic acid and dioxane molecules
whereas in the solutions of benzoic acid in benzene there is no formation of such hydrogen
bonds.
The studies of Nambinarayanan et al. (1978) on the variation of internal pressure with
concentration in benzoic acid and oxalic acid in dioxane have shown a maximum where
maximum hydrogen bonds are formed between monomer carboxylic acid and dioxane. The
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complex formation between dioxane and certain solutes such as benzoic acid, succinic acid,
and oxalic acid had been reported.
Rajendra Naidu (1985) has measured sound velocities in aqueous solutions of sodium
benzoate and sodium phenyl acetate and densities and sound velocities in aqueous solutions
of sodium salts of m-nitrobenzoic acid, m-toluic acid have been measured at four different
temperatures (25, 35, 45, and 55C) from which the apparent molal volumes (g,) and
apparent molal adiabatic compressibility ( 3 ave been obtained. The results indicate that 4,
VS
m :
nd
,
vs m ? curves are straight lines for all the salts in the concentration range
studied. The derived limiting apparent molal volumes (4, ) and limiting apparent molal
adiabatic compressibilities (4;) have been examined for specific effects in the hydration
behaviour of the substituted arom atic acid salts. The , and values increase with
tempera ture for all the salts in the temperature range studied . The results were explained in
terms of solu te-solvent and solute-solute interactions
Ultrasonic absorptions in the solutions of oxalic acid dihydrate and benzoic acid in
dioxane were measured by Srinivasa Manja (1985). The classical absorption was less than
the observed absorption, and excess absorption was found to be 4 to 6 times that of the
classical absorption. It was concluded that the molecules in the system appears to be in two
states, and this result was more useful in elucidating the nature of molecular interactions than
the quasichemical model.
Ultrasonic velocities in aqueous ethanolic solutions of monochloroacetic acid have
been measured by Nikam and Hasan (1986) in the concentration range 0.05-0.4 moll1 at 25.
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30,
35, and
40C.
Specific acoustic impedance, molar sound velocity, molar compressibility,
relative association, and solvation number have been evaluated and discussed in the light of
solute-solvent interaction.
The ultrasonic measurements were carried out by Nambinarayanan et al. 1988) in
non-aqueous solutions of malonic acid, maleic acid, and cinnamic acid in dioxane and
aqueous solutions of malonic acid and maleic acid. The concentration range studied were
from
0.01
to
0.1
mole fractions at different temperatures. The ultrasonic velocity showed two
maxima in the concentration ranges, in non-aqueous solutions, while a non-linear variation of
the velocity in the concentration ranges in the case of aqueous solutions. The other
parameters were calcu lated . The results indicate the possibility of formation of hydrogen
bonding of
0 - H
type and
C-H
type in the non-aqueous solution, and weak association
due to hydration in the case of aqueous solution.
Ultrasonic velocity studies were carried out by Sosamma et
al
1988) in solutions of
o- and p-hydroxy benzoic acid in dioxane at various solute concentrations ranging from
0.01
to 0.1 mole fraction at temperatures
308K,
313K, and
323K.
The variation of ultrasonic
velocity in both solutions in the solute concentration showed two velocity maximum, one at
lower solute concentration and the other at higher solute concentration. These maxima
indicate complex formation between OH and COOH groups of the solute with the free
oxygen of the dioxane. These studies also indicate that the ultrasonic velocity is higher in the
non-chelated compound than the chelated compound at any solute concentration.
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The ulhmsonic velocity and density of the solutions of phenol, a-nap thol, and benzoic
acid in benzene and 1,4-dioxane were measured by Om ch ow sk i and Em st (1988). The
results discussed in the light of Jacobson s association model, indicate the importance of
different types of intermolecular interactions in the determination of ultrasonic velocity in
liquids.
Ultrasonic velocity, density, and viscosity measurements have been made of solutions
of urea, thiourea, acetamide, d imethyl urea in the water-dioxane system by M isra et al. (1988)
at different temperatures. Partial molal volume
O,),
partial molal compressibility
( ,),
Vand s
interaction coefficients
(Q,
V) and the thermodynamic activation parameters
G .
S*, and
Hi) of these solutions have been computed. The results are interpreted in terms of
solute-solvent interactions.
Ultrasonic absorption measurements were made by Agnihotri and Adgaonkar (1989)
using sender-receiver technique in binary liquid mixtures of n-hexane benzene, methanol
n-hexane, butanol n-hexane, methanol + benzene, butanol b e m n e , n-hexane acetone,
benzene acetone at a frequency of
2 M z
and at a temperature of 3 13K. Viscosity is also
reported for these liquid mixtures. The results are discussed in terms of the structural effect
of n-hexane and benzene.
Acoustic investigations of three binary mixtures of organometallic compounds-
tetrabutyltin, tributyltin chloride and dibutyltin dichloride
-
with tetrahydrofuran have been
made by Singh and Kalsh (1991) at 4SC. A large number of acoustical and
thermodynamical properties, such as molar sound velocity, molar adiabatic compressibility,
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acoustic impedance, surface tension, available volume, co-volume, intermolecular free length,
and relative association have been evaluated for the systems. Excess parameters such as
excess ultrasound velocity, excess density, excess molar sound velocity, excess molar
adiabatic compressibility, excess acoustic absorption have been calculated. All the three
systems studied here are non-ideal, and results have been used to interpret the relative order
of the acceptor strength of the butyltins.
Ravichandran et al. (1994) carried out ultrasonic velocity studies in the solutions of
oxalic acid in tetrahydrofuran at 303, 313, and 323K. The measured ultrasonic veloc~ty
increased nonlinearly over the entire concentration range studied. The results were discussed
on the basis of formation of hydrogen bonds between the oxalic acid monomers and the free
oxygen of tetrahydrofuran molecules.
The apparent molar volume 4,) of calcium acetate was determined in 10, 20, 30, and
40 aqueou s acetic acid at different temperatures by Blokhra et al. (1992). Results were
interpreted in terms of solute-solute and solute-solvent interactions and structure
makingistructure breaking capacity. Calcium acetate was found to be a structure breaker.
The ultrasonic velocity, density, and viscosity were measured by Kannappan et al.
(1992) for five ternary mixtures of acetic acid, propionic acid, and butyric acid with aniline
and acetic acid and propionic acid with pyridine in a non-polar solvent benzene. The
acoustical parameters such as adiabatic compressibility, free length, free volume, and internal
pressure were obtained from the experimental data for all the mixtures. The results indicated
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the presence of strong hydrogen bonding interaction as well as the charge transfer complex
between amine and carboxylic acid in benzene.
1 5 3 ELECTROLYTES AND NON ELECTROLYTES
The study of ultrasonic velocity and adiabatic compressibility in aqueous solution of
electrolytes and non-electrolytes is of paramount importance, as it provides information about
the nature of molecular interactions. Extensive work has been carried out by a number of
workers in this area and the parameters such as adiabatic compressibility, apparent molal
compressibility, and hydration numbers have been determined in aqueous solutions of
different electrolytes. For aqueous solutions of electrolytes cadmium bromide, cadmium
iodide, zinc iodide, and strontium iodide, the ultrasonic velocity studies have shonn a
decrease of sound velocity with increase of concentration of the electrolytes Balachandran,
1960). This is contrary to the general observation that the sound velocities are more
than
that
of water in aqueous electrolyte solutions. However, the decrease in ultrasonic velocity
observed in this case was explained as due to the presence of heavy ion. Heavy ions have
smaller velocity of Bronnian motion. The apparent molar compressibility of the electrolyte
solutions provided information on the state of dissociation
of
the electrolyte in aqueous
solutions. Similar observations of decrease in ultrasonic velocity with the increase in the
concentration of electrolytes have been reported in the case of aqueous solutions of calcium
iodide, zinc bromide, and silver nitrate Rao et al., 1961). The plot of molar sound velocity
against solute concentration is linear and the gradient seems to depend on the valency of the
solute Murthy et al., 1963).
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The complex formation of aluminium sulphate and scandium sulphate was studied by
Berger et al. 1978) in aqueous solutions using ultrasonic relaxation techniques in the
frequency range 0.23 to 1500 MH z. Two and three chemical relaxation effects were observed
for 32 solutions of aluminium sulphate and scandium sulphate respectively, which are
onsistent with a three step association mechanism.
For scandium sulphate, rate and
equilibrium constants s well s volumes of reaction were obtained for all three reaction steps
by analysis of relaxation times and amplitudes.
Ultrasonic relaxational absorption w s observed in the solutions of Nal in i-PrOH by
Okuwa and Ohno 1981). Assuming the excess ultrasonic absorption to be caused by the
relaxation of dissociation equilibrium of NaI in the solutions, the dissociation and
recombination rates of NaI, the Arehenius activation energy, and the enthalpy and volume
changes due to association were calculated; these were compared with the values estimated
from other methods. An increase of the dissociation constant of Nal was observed with an
increase of H,O in i-PrOH-H,O mixtures.
The absorption of sound in aqueous solutions of alkali halides decreases with
increasing concentration irrespective of the frequency Endo et al., 1981). The mechanism
for this sound propagation is explained by a kinetic model describing the behaviour of the
nearest neighbour water molecules around the ions.
Free volumes PI ave been evaluated for aqueous solutions of p-dioxane, pyridine,
N-methylformamide NMF) and N,N-dimethylformamide DMF) as a function of
Concentration by Manohara Murthy and Nagabhushanam 1984) using the ultrasonic velocity,
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density, and heat capacity data at 298.15K. V, is found to be minimum at
X,=
0.16,0.23,
and 0.25 for p-dioxane, pyridine, NMF, and DMF respectively. These results indicate the
formation of 5: 1 water-dioxane and 3: 1 water-pyridine, water-NMF and water-DMF
complexes.
Adiabatic compressibilities have been calculated from ultrasonic velocity
measurements by Venkatesan et al. (1986) for solutions of sodium and potassium acetates in
10 WIW
acetic acid-water mixture. From this data apparent molal compressibilities have
been calculated. Attempts were made to explain the variation of ultrasonic velocity with
concentration in terms of variation in compressib il~ty nd density. From the compressibility
data presented it was concluded that both salts are stmcture makers.
The measurement of velocity of propagation of ultrasonic waves has been used by
Ogra et ai. (1988) for the determination of thermodynamic parameters for sodium citrate in
water at different temperatures and concentrations. The ultrasonic velocity, density havr
been used for the computation of adiabatic compressibility
P,),
spec if i~ ~ ~ u u s t ~ cn ~ p c d ~ : : ; .
(Z). apparent molal compressibility O,), molar sound velocity (R), relative association (RA),
and intermolecular free length (LJ. The absorption together with ultrasonic velocity and
density have been used to compute mechanical (Q)
and
relaxation time r). The variation of
a iP has been studied at different concentrations and temperatures.
Relative hydration numbers, H of 50 non-electrolytes in the temperature range
273-308K were determined by Juszkiew icz (1989) by measuring the maximum velocity of
ultrasound in solutions of the following binaq solvents; water-ethanol, water-n-propanol,
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water-acetone, water-tetrahydrofuran, and water-dioxane. Contributions to total hydration of
alkyl groups and of different hydrophilic groups were also evaluated. The structure of the
solution of these non-electrolytes is described qualitatively on the basis of the hydrogen
bonded framework model of the water structure.
Mixtures of water and DMSO were prepared in a particular weight ratio (20 DMSO
80 water) and the homogeneous systems was allowed to attain room temperature. The
required quantity of the non-electrolyte urea for a given molality was then dissolved and
filtered. Free volume and internal pressure were evaluated using the experimentally
determined ultrasonic velocity, density, and viscosity of the solution (Pillai eta ]. . 1989).
Apparent molar volumes of univalent salts have been studied in dioxane water
mixtures by Das (1989) at 10. 20, and 30 (by UT. ithin the temperature range 30-45'C
and ion-solvent interaction has been inferred.
The expression on sound absorption and sound dispersion in aqueous solutions of
non-electrolyte has been obtained by Endo (1990) based on the idea due to hydrophobic
interactions. The calculations are shown to be in agreement with the observation on butyl
cellulose (ethylene glycol monobutyl ether) aqueous solutions. It is shown that the relaxation
curve is expressible in terms of two relaxation times the upper relaxation time,
corresponding to the usual intermolecular relaxation time hitherto employed, and the lower
relaxation time, shortened under the influence of the diffusion of the molecules.
Measurements of absorption coefficient of ultrasonic waves have been made by Piotr
Miecmik (1990) within the frequency range 10-100 MHz in aqueous solutions of
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N-meth~ lace tam ide O'JMAA) and zinc chloride (ZnCI,).
The method used to prepare
quasi-two-component solutions permitted a change in the ratio of number of amide molecules
to electrolyte molecules , given a constant number of water molecules. The results indicate the
occurrence of a single relaxational process in the solutions under investigation and the
frequency range adopted. On the basis of theory of relaxational absorption of sounds,
relaxation parameters as well as the enthalpy of activation of the solution in question, which
was 16.4 KJImol, have been calculated. The character of the relaxational process observed
was determined o n the basis of the analysis of relaxational curves. The discovered
relaxational process in H,O-NMAA-ZnCI, was ascribed to the formation and degeneration of
'salvatomers' composed of (NMAA Zn(H,O),) .
Aqueous solutions of CF,COONa have been studied with ultrasonic methods by
Berchiesi and Farhat (1992). Excess sound absorption has been generally observed, and in
the most concentrated solution, a dependence of a P on the frequency was also put into
evidence.
An
anomalous trend of
alp
observed in solutions, has been correlated to the
micellar nature of these solutions.
Experimental data for ultrasonic velocity, density, and viscosity in aqueous solutions
of Co(CH,C00),.4H,O, CoBr,.6H,O and CoF2 .4H,0 at 304.8K were reported by Das et al.
(1992). The data were used to compute thermo-acoustic parameters of the salt solutions for
studies of the kinetics o f interaction.
Ultrasonic, volumetric and viscometric measurements have been performed by
Pandey et al. (1992) on aqueous solutions of D(+)ribose at 10, 15, 20, 25, and 30C. These
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measurements have been used to evaluate some important ultrasonic and thermodynamic
parameters viz., apparent molal volume
O
apparent molal compressibility
O
partial molal
compressibility
go
the viscosity B-coefficient of the Jones-Dole equation, the free energy of
activation for viscous flow
AG,
entropy
AS
and enthalpy of activation
AH.
These parameters
have been used to interpret the results in terms of solute-solvent interactions. The structural
interactions of ribose and its derivatives with water molecules have been interpreted
successfully.
Using a single crystal variable path interferometer, ultrasonic velocity was determined
in aqueous solutions of rare earth nitrates near the temperature of the sound velocity
maximum and adiabatic compressibility minimum. The study indicated that neodymium and
gadolinium nitrates behaved as structure makers even at high temperatures, and the results
were discussed in the light of the structure making properties of both neodymium and
gadolinium nitrates Moosavi et al., 1988).
Ultrasonic absorption, velocity, isentropic compressibility, relaxation time, and
relaxation amplitud e measurements were reported on poly vinyl chloride) PVC ) solutions in
two different solvents dioxane and butanone at 239K. The results showed linear increase of
velocity, density, and viscosity with increasing poly viny1 chloride) concentration in the two
solvents. In contrast, the isentropic compressibility, relaxation time, and relaxation amplitude
were found to decrease with increasing PVC concentration. This suggested interaction
between PVC and the solvent molecules Hassun et a] ., 1989).
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Ultrasonic velocity and absorption measurements were undertaken in aqueous
electrolytic solutions of ammonium chloride, ammonium dihydrogen phosphate, and
ammonium oxalate. The non-linear increase in the ultrasonic velocity and decrease in the
observed absorption were discussed on the basis of Flickering-cluster model and Hall's
two-state model for liquid-water (Ravichandran et al., 1991a).
Self diffusion coefficients of water and of 1-propanol have been determined in the salt
free mixtures and in NaI solution at 25'C. Assuming perfect slipping boundary conditions,
hydrodynamic radii of both components have been calculated. Their values have indicated
that diffusing units of water and of I-propanol were not the single molecules. In aqueous
solutions below 20 mol of alcohol clusters have been found. In alcohol rich mixtures, above
50 mol PA, motions of water molecules were strongly correlated with those of alcohol
ones, which indicated that a water molecule was able to co-ordinate up to the alcohol
molecules. In
Nal
solutions, because of preferential hydration of sodium ions, such
a
phenomenon does not exist (Hawlicka et al., 1992).
John Paulus et a l. (1986) measured ultrasonic velocity of the ternary system consisting
of water, 2-propanol and nitromethane at 35C for different proportions of the components.
Adiabatic compressibility, molar sound velocity, free volume, and internal pressure were
calculated. The observed increase in adiabatic compressibility and free volume with increase
in mole fraction of 2-propanol suggested polymerisation or ternary pseudo molecules.
Measurements of densities of solution of
AgNO
and CaRJO,), in the mixed solvents
water-methanol and water-acetonitrile were carried out at 25C and the partial molar volume
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of these electrolytes were determined by Fumio et al. (1991) by taking into account of the
concentration dependence of the apparent molar volumes predicted by the Debye-Huckel
theory. The ionic partial molar volumes of Ag , Ca2 and NO3-were evaluated, and compared
with those of other ions in the two mixed solvent systems. The solvent composition
dependence was more remarkable in water-acetonitrile than in water-methanol, and
characteristic behaviour was observed for Ag* and Ca2 ions in water-acetronitrile system.
The ultrasonic velocity, absorption, density, and viscosity of the solution of
Th@ 10j) 0,.6H 20 and La(N 03),.6 H,0 in methanol was measured by
Das
et al. (1990) at room
temperature. The classical absorption was found to be increased with increasing concentration
in both the salt solutions. The results were discussed in the light of long range ordering of the
solvent molecules under the influence of the electrostatic field of Th4 and La2- ons.
Ultrasonic velocities and densities at 30C have been determined experimentally and
isentropic compressibility, intermolecular free length, molar sound velocity, specific acoustic
impedance, molal isentropic compressibil ity, and solvation number have been computed for
the alcoholic solutions of thorium nitrate in methanol, ethanol, isopropanol, and n-butanol.
The results were discussed in the light of existing theories of ion solvent interaction (Prasad
et al., 1988).
Ultrasonic velocities in solutions of monochloroacetic acid in ethanol-nitrobenzene
mixtures were measured at
25, 30, 35,
and
40C
by Nikam et al. (1991) . The related
parameters were calculated. Bachem and Gucker s laws have been found to be valid.
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Excess internal pressure of binary liquid mixtures of cuemene with
n- pr op an ~l , nd n-butan01 at 30, 35, and 40C and ternary liquid mixtures of di~ h lo ro m et han ~
with methanol benzene, benzene propanone, and methanol proponone at 30C has been
evaluated by Shukla et al. (1992) from ultrasonic velocity measurements. The proposed
method involved the use of molecular diameters. It has been found that it provided useful
information on the study of intermolecular interactions in binary and ternary liquid mixtures.
Ultrasonic absorption, velocity, adiabatic compressibility, relaxation time, and
relaxation amplitude measurements were reported by Hassun (1985) on poly (vinyl chloride)
solution in tetrahydrofuran (T HF) at 313K. Results showed a linear increase of velocity,
density, viscosity, absorption, relaxation time, and relaxation amplitude values with the
increase of PVC concentration in TH F. In contrast. the compressibility decreased with
increasing PVC concentration. This suggested interaction between PVC and THF molecules.
The excess molar volumes of mixing (&VC and compression of mixing [&(PV)' ]
have been calculated from the measured density and sound velocity parameters for aqueous
binary and ternary solutions of NaCI-KCI, LiBr-KBr, RbBr-KBr, CsBr-KBr, Me,NBr-KBr,
Et,NBr-Me,NBr and Bu,NBr at 25OC by Patil et al. (1988). The study indicated the presence
of
cation-cation interactions. The results were discussed in terms of the combination of water
structure breaking and structure making properties of ions.
Sastry (1983) has measured the ultrasonic velocity using 90%-13% water-dioxane
mixture as the solvent six EDTA-metal chelates due to ( I ) EDTA+AICI,, (2) EDTAtCuSO,,
(3) EDTAtNiSO,,
(4)
E D T A ~ C ~ S O , ,5) EDTA+BaCI,, and (6) EDTA+KNO, at 30C and
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~ H = 3 .5 . The experimental results have been discussed on the basis of B j e r r ~ m ~heory of
ion-association. The results of these chelates in water-dioxane mixture have been compared
with those obtained when water was used
s
solvent. Less dielectric constant of the medium
has been found favourable to the extent and as well as scope of chelation.
Acoustical parameters namely adiabatic compressibility, free length. specific acoustic
impedance, and relative association have been computed from the experimental data in the
solutions of tetramethylammonium bromide and tetrabutyl ammonium in dioxane-water
mixtures at 303.15K. The result revealed the nature of solute-solvent interactions in these
solutions (Rajendran, 1994).
The ultrasonic and viscosity measurements of yttrium soaps (caprylate, caprate and
laurate) in a mixture of benzene and dimethylformamide (3:2). It may be concluded that
yttrium soaps behave as simple electrolytes in dilute solutions, and the electrsostrictive effect
of the ions on the polar solvent
DMF)
olecules in the immediate vicinity of the ions was
greater than on non-polar solvent (benzene) molecules.
The
results confirmed that there was
s significant interaction between soap-solvent molecules in dilute solutions (Mehrotra et al.,
1992).
Density, viscosity, and ultrasonic velocity were measured in solutions of ammonium
nitrate and tetraalkyl ammonium salts tetra methyl ammonium chloride, tetra ethyl
ammonium bromide and iodide, and tetra-n-butyl ammonium bromide and iodide in different
composition of water 2-methoxy ethanol and water 2-ethoxy ethanol by Dash et al.
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(1994). The results were discussed in terms of ion-solvent and ion-ion interactions and of
effects of the solvent.
The molar volumes of cadmium bromide and cadmium iodide in aqueous ethylene
glycol (10,
20,
30, and 40 WIW) were reported in the temperature range 30-45'C by
Blokhra et al. (1988). The limiting apparent molar volume was determined from Masson
equation. The value of $, increased with the increase in temperature showing that these salts
behaved as structure-makers in aqueous ethylene glycol. Ion-solvent interaction decreased in
case of bromide ions, and increased in case of iodide ions with the increase in ethylene glycol
content. The temperature effects suggested that at 30 ethylene glycol, bromide ions were
more solvated than iodide ions.
Syal et al. (1992) measured sound velocities and densities of lithium, sodium, and
potassium bromides and some tetralkylammonium iodide in dimethyl sulphoxide. dioxane,
and dimethyl sulphoxide
+
dioxane mixtures at
2
MHz
at 25'C and reported that
intermolecular forces were increasing with the addition o f electrolytes.
Four salts Et4NI, Pr,NI, B q N I and P eh NI were examined by Pathak et al. (1992) in
formamide -
MSO
from the point of view of apparent molal volume $, study by the
magnetic float densitometer method. The trend in
t .
nd hence the nature of the slope 4 vs
c ' ' ~urves was studied for these salts. Pr,NI, Bu,NI, and Pe&NI show transition in the sign of
slope in dilute solutions, but they show positive slope in concentrated solutions. Et4NI has
Positive nature in its slope in lower as well as in higher concentrations. The high ionic
interactions favour positive slope while weak ionic interactions lead to negative slope.
4 1
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Ultrasonic velocity measurements were done in three ternary liquid mixtures of
toluene. benzene and 1-4dioxane with cyclohexane in chloroform. Th e isentropic
compressibility suggested the existence of specific molecular interactions between the
components of the mixtures Kannappan et al., 1990).
1.5.4 BIOLOGIC L MOLECULES
Measurements of absorption and velocity of sound in blood, plasma and solutions of
albumin and haem oglobin have been reported by Cartensen et al. 1953) in the frequency
range 800-3000 KHz and at the temperature range
5 4S0C.
The absorption departs only
slightly from a linear dependence upon frequency. Absorption for the various solutions is in
direct proportion to the protein content. It is concluded that the acoustic properties of blood
are largely determined by the protein which it contains.
Goto et al. 1964) have studied the hydration numbers of various am ino acids,
oligopeptides, and saccharides in aqueous solutions, and their dependence on the temperature
h a . been determined by the method of ultrasonic interferometry. The hydration of ionic.
hydrophilic and hydrophob ic sites have been discussed. Particularly, evidence for the
hydration around the hydrophobic groups has been obtained.
Ultrasonic velocity and attenuation in aqueous solutions of glycine, diglycine,
triglycine, p-alanine, P-aminobutyric acid, aspartic acid, and L-glutamic acid have been
measured as a function of pH by Applegate et al. 1968). From the dependence of absorption
on pH, it was concluded that the perturbation of proton transfer equilibrium was the process
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responsible for the observed excess ultrasonic absorption in these amino acids and simple
peptides.
Ultrasonic velocity and absorption in dilute solutions of 12 amino acids were
measured over a wide pH range. Ultrasound velocity, volume and compressibility changes in
amino acid solutions due to ionisation of amino and carboxyl groups were evaluated. The
mutual influence of the amino and carboxyl groups on the hydrational volume and
compressibility has been estimated qualitatively, Ionisation of amino group decreased partial
molar +olume and increased partial molar compressibility of water in the hydration shell of
the solute. Ionisation of a carboxyl group decreased both partial molar volume and
compressibility of the hydrated water Chalikian et al ., 1992).
Ultrasonic velocity was measured by Gerecze 1975) in dextran and d-glucose
solutions at 814 KHz and at different temperatures. In dextran solutions the dependence of
compressibility on concentration can be explained by the interaction between dextran and
water molecules, whereas its dependence on temperature may be due to the changes in the
structure of water. According to their calculations, the structural change of water can be
attributed to the fact that in dextran solutions, the ratio of water and bound d-glucose is less
than that of water in d-glucose solutions.
arvazyan et al. 1979) have performed the ultrasonic velocity titrations in aqueous
solutions of glycine, alanine, and histidine. All systems were studied in the pH range 5-13.
The more acidic process showed a symmetrical behaviour about pH=pK . All the amino acids
studied showed an asymmetric behaviour if the pH is above 9. This asymmetry i s due to a
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relaxational velocity dispersion which occurs for the deprotonation reaction. This effect has
its maximum value at a pH near
11.
The titration curve can be corrected for this effect by the
studies of absorption of sound.
When corrected, the titration curve can be interpreted in
terms of hydration ch anges which accompany the reaction. It is found that the
NH,
group
jn glycine is the most hydrated.
The
other amino acids show lower hydration due to steric
effects. These results were extended to protein and metmyoglobin. This substance shows
three inflections in the titration curve. These correspond to titration of histidine residue. free
NH,
groups (including a relaxational contribution) and a velocity change due to
denaturation of the protein by base. Semi quantitative agreement is found between the
theoretical and experimental titration curves.
Ultrasonic velocities have been measured in aqueous solutions of glycine in the
concentration range 0.05 to 2 molality by Lark et al. 1984) at 25, 30,35, and 40C. Adiabatic
compressibilities, apparent molal compressibilities, hydration numbers, and other related
parameters have been calculated. The temperature dependence of apparent m old
compressibility hints towards the partially independent contributions of positive and negative
parts of the glycine zw itterion.
Panial molar volumes of various species of six a-amino acids viz., as ~artic cid,
glutamic acid, lysine, arginine, alanine, and glycine were determined by Rao e. al. 1984) at
20C from the pH-dependent density data of their aqueous solutions. In ich system, the
amino acid species having the highest number of charges has the lowest par lal molar vo lume.
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Rao et al. (1984a) have described a method of estimating partial molar volumes of
a-amino acids in water, starting from the partial molar volume of glycine. For eleven
zwitterionic amino acids. the estimated partial molar volumes are found to be in very good
agreement with the experimental values given in the literature. Amino acids having ionisable
side chains can exist in aqueous solutions as different ionic species: the partial molar volumes
of these obtained from the densitometric studies have been compared with the estimated
values. The method has given
good results for the ionic species of lysine and arginine,
where the charge centre in the side chain is well separated from a- NH, and
a-COO-.
but not
for all species of aspartic and glutamic acids.
Rao et al. (1988) determined the partial molar volumes of the following mixtures in
water at
2 C:
(i) glutamic acid glycine; (ii) argin ine glycine; (iii) arginine: glutamic acid;
(iv) arginine aspartic acid; v) lysine glutamic acid; and (vi) lysine aspartic acid. Partial
molar volumes of the mixtures calculated using partial molar volumes of the various ionic
species of the amino acids agreed
with
the experimental values for systems (iii) to (vi). The
positive deviations, of the experimental values from the calculated values re discussed in
terms of spec ific interactions between ionogenic side chains. The extent of interaction is
greater in sys tems containing aspartic acid andlor arginine.
Hydration numbers of the simplest carboxylic acids. amino acids and di- and tri
peptides were determined by Adam Juszkiewiz (1985) by measurements of ultrasonic
velocity in the ethanolic aqueous solutions.
Hydration numbers of the functional groups
Present in the amino acids and peptides were also determined
5
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Ultrasonic velocity hydration numbers of diamines, triamines and tetraamines, and
hydrochlorides of these m i n e s were determined by Juszkiewicz and Figlerowicz (1990) by
measuring the maximum velocity of ultrasound in aqueous ethanolic solutions. The resu lts
are interpreted on the basis of the hydrogen-bonded framework model of the water structure.
Nambinarayanan et al. (1989) have observed that the addition of small quantities of
strong structure breakers of water generally seems to increase the cohesion among the
molecules by breaking the open structure. In aqueous solutions of DN A, the concentration
0.07 to 0.08 seems to be important
s
it decreases the close packed content of water
structure, and brings down the ultrasonic velocity below that of water. Similar behaviour is
observed in L-proline. In the case of dilute aqueous solutions of glycine, there seems to be
reduction of close packed structure of water initially. These studies also indicate that the
structure breaking properties of the three biological molecules (DNA, L-proline, and glycine)
seem to be in decreasing order, it being large in DNA and small in glycine.
Wang Jin et al. (1990) used an automated version of the resonance method to measure
the velocity titration curves of several amino acid solutions in the pH range 1-13 at 20C and
at
a frequency of MHz. The results show that the velocity increment in the neutral aqueo us
solution is larger because the am ino acid molecules exist in the dipolar form and thus have a
stronger interaction with the surrounding water, and the loss of ionisation of a group by
titration decreases the velocity because of the increased compressibility resulting from the
decreased electrostrictive compression of water around the amino acid molecule with
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hanging pH. theoretical model was developed to describe the sound variation process,
which compared well with the experimental data.
Absorption of ultrasound in L-cysteine has been measured by Holmes and Challis
(1989) at 37'C for the pH range 6.8-8.0 for 0.2 and 0.5 mol dm solutions. new pulse
transmission technique has been used, which produces continuous absorption spectra for the
range
2 50
MH z, enabling accurate determination of relaxation frequency (f,) w ~t hin his
range. The variation o f f , with concentration and pH is explained in terms of mechanisms
involving both intra- and inter-molecular proton transfer. For the first time, values have been
dctcrmined for the volume change of the intra molecular proton-transfer reaction, and for
number of the individual ionization rate constants for cysteine.
Ultrasonic absorption and velocity studies were carried out and analysed by Hussey and
Edmonds (1970) in aqueous glycine solutions in the range of frequencies 10-130 MHz in the
pH range 0.96-1 1.6 for single relaxation behaviour. Activity coefficients were calculated by
three methods: the method based upon standard ionic radii and the mean dielectric constant is
found to yield the most acceptable estimates. The dependencies of the rate constants upon
initial concentration of the solute, ionic strength, and temperature are determined in the range
0.25M-1.OM and 22-37OC, respectively. It is concluded that proton-transfer reactions of
amino and carboxyl groups are not responsible for significant contributions to the total
ultrasonic coefficient of blood in the physiological range of pH.