CHAPTER I

INTRODUCTION AND REVIEW OF LITERATURE

CHAPTER I

INTRODUCTION AND REVIEW OF LITERATURE

1.1 INTRODUCTION

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 with concentration of

one of the components, helps to understand the nature of molecular interactions in the

mixtures. Owing 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 confinnational

analysis of organic molecules (Bergelson, 1960). Several empirical and semi-empirical

formulae have been developed correlating velocity and attenuation with other molecular

parameters, and a brief account of theoretical aspects are given below.

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

c2 = (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

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 solute 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 volume. 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 Yo is the volume at absolute

zero). The intermolecular free length depends on the type of packing, and the extent of

association in a given liquid.

From the study of adiabatic compressibility and L, in the case of non-associated

organic liquids, Jacobson (1951) has shown that the plot of log P, against log L, is a linear

one suggesting a relation of the type

PI = KL; (1.9)

where K and x are constants and the values of the constants x and log K are 2.082 and 7.097

C.G.S units at 20aC in the case of non-associated liquids. The free length L, calculated using

the relation (1.8) agrees with the free length calculated using the relation (1.9) and the

maximum deviation being approximately 3%, and this is attributed to uncertainties of the

parameters in equation (I .8).

The computation of the free length for mixtures of liquids from molar volumes has

been extended by Jacobson (1952) by revising the definition L,= 2 V,N as

where X,, X, and V,", V,B represent the mole fractions and volumes at absolute zero of the

liquid components A and B respectively, and V, stands for molar volume of the mixture.

Y, and Y, are the surface areas of the molecules of the components. The free length

computed from the compressibility data according to equation (1.9) agrees well with that

calculated for mixtures from molar volumes. The average error being less than one

percent. This constitutes the strongest evidence of the applicability and the utility of equation

(1.9) for liquid mixtures."

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 aW2 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 cohesion process under normal circumstances. Cohesion creates a pressure of 10'

to lo4 atmospheres 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 solute 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

(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 alp where a is the coefficient of thermal expansion, and p is the isothermal

compressibility. As a lp has a large value, and as such P can be neglected in comparison to

T (SPIST),. Hence the equation reduces to

since p = y p,, this equation also can be expressed as

p -ro ' - UP,

where y 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 of 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 isestimated, for

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example, for a binary liquid mixtures using the relation

- "1P,:l.:'P2 T-- (1.13)

where n, and n, are the number of moles of the components and D l and p, are the

compressibilities of the components, and pT is the compressibility of the ideal mixture. In

certain liquid mixtures which deviate from ideal behaviour, the experimentally determined

compressibility (P,) will be different from that of calculated adiabatic compressibility (P,).

The difference between these two is called excess compressibility, and it is given by

Pt = (1.14)

(Narayanaswamy et al., 1981).

1.2.6 EXCESS VOLUME

When two liquids are mixed together the volume of the mixture is a function of

the component volumes. If V10 and V: are the molar volumes of the pure components, and

Vl and V, are the partial molar volumes of the solution at molar concentration X, and X,, the

molar volume change AV on mixing is given by

*V=X1V, +X>V, - (x& +x*e) = VI - # + ((VZ - e) - ( ~ 1 - q)) x2 (1.15)

The change in volume AV is known as the excess volume, and it may be positive or negative

depending on the nature of interaction between the molecules (Moelwyn-Hughes, 1964).

1.2.7 EXCESS INTERMOLECULAR FREE LENGTH

With the help of thermodynamic parameter of intermolecular free length of the

pwe liquids and those of the mixture, the excess intermolecular free length L: can be thus

computed.

Lf = 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 the 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 0°C. It 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 of water at O°C (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 ultmonic absorption 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~ties of the sound before and after passing

through a layer of thickness X, then

I = ( oe -20~X (1.17)

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 Np 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 is found to be higher than the classical

I0

absorption. The difference between these two absorptions is termed as 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 THERMAL 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

11

where intermolecular forces are fairly strong. In these liquids, the molecules are assumed to

be in two structurally different arrangements. The time lag in exchange of energy between

two different structural arrangements is termed as structural relaxation.

If the structural fluctuation perturbs the equilibrium of the components of a molecular

relaxation process, then the thermodynamic coefficient depends not only on the equilibrium

thermodynamic variables, but also on the extent to which the reaction has proceeded towards

its local equilibrium. The bulk modulus, for example, becomes a complex function of

acoustic frequency (a) as given below:

e=em+,; and hence

P o = P = + P r

where r represents the relaxation time. and p, the contribution to p caused by relaxational

effect, and is the compressibility at high frequency and j = f i , P, is the compressibility at

low frequency.

The significant of P,, P,, and P, can be realised, if one considers that the liquids can

exist in two energy states (1) and (2) having energy values W, and W, respectively. For the

lower state W, , the volume is larger than for the higher state W,. Here, P, represents the

compressibility for the higher state. At lower frequencies, where there is sufficient time for a

complete transfer of energy from state (I) to state (2), P, will be equal to Po, P, is the

compressibility which corresponds to the lower state. At very high frequencies, where there is

no time for any energy to flow from state (1) to state (2) P is equal to Po. Hall (1948)

considered that (1) and (2) were states of equilibrium separated by a potential barrier of AF,

and obtained an expression for the relaxation time T as given below

where 7 , is the shear viscosity, V molar volume of liquid, $ is the gas constant, T 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 solid. 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:

13

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) as

@ 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

r = ~ ~ ( 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 entire group of

14

three or more atoms, which are involved in a configuration X-H-Y, where X and Y may be

like or unlike atoms. 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+XHY lying in most cases in the range 2 to lOKCal/mole.

Hydrogen bonding is found with strong electronegative atoms like F, 0, N, CI, etc The

atom X or Y is one of these electronegative atoms in the configuration X-H-Y. Increasing the

electronegativity of 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 SPECTROSCOPY

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

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. A non-linear molecule that contains N atoms 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 bond 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 confirmed

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.

1.4.2 HYDROGEN BONDING AND IR SPECTRA

Hydrogen bonding has been recognised as an interaction between an X-H group of

molecule with an Y atom, usually of another molecule. Since the force field around hydrogen

atom is modified as a result of the formation of the X-H-Y bond, the X-H vibrational bands

are altered. The X-H stretching band, which is usually sharp in the unbonded state usually

becomes broader and more intense and is shifted to lower frequencies upon the formation of

hydrogen bond. The amount of X-H frequency shift upon formation of the X-H-Y bond has

been correlated with the X-Y distance. the smaller the distance, the larger the shift (Ferguson,

1969). The change in the frequency between the free 0-H absorption and bonded 0-H

absorption is a measure of the strength of the hydrogen bond, and this enables one to

calculate the probable average hydrogen bond length.

1.5 REVIEW OF LITERATURE

Ultrasonic velocity and absorption measurements in liquids and liquid mixtures find

extensive application to study the nature of intermolecular forces. An excellent review of the

work carried out on large number of liquid mixtures is given by Nomoto (1956) and Schaaffs

(1954). The liquid mixtures can be broadly divided into two groups, viz., I and 11. In group 1,

the velocity variation with concentration of the solute is non-linear, whereas group I1 exhibits

velocity maximum or minimum (Nomoto, 1953). The ultrasonic studies in liquids and liquid

mixtures were interpreted using Schaaffs' collision factor theory. and Jacobson's free length

theory. Excess parameters, i.e., the difference between molecular and physical properties of

the solvent and the mixture have been estimated using Flory's theory. 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 MIXTURES

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 30°C in ternary liquid mixtures of acetonitrile-carbon tetrachloride-n-butanol;

dioxane-cyclohexane-chloroform. The increase in free length in the solutions due to the

18

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 compressibilit~es in binary ~lquid mixtures of

aniline + phenol, quinoline + phenol and pyridine + phenol have been studied by Adgaonkar

et al. (1977). 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 of these

mixtures. The complex formation through hydrogen bonding for the above liquid mixtures

have been observed. From these studies, it was inferred that the complex formation was

stronger in the case of pyridine + o-cresol mixture and weaker in others.

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.

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 45°C 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 (bN1; where R = C, to n-C,) in dimethyl sulphoxide has been carried out by Pankaj

and Sharma (1991) at 40, 50, and 60°C. 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 308.15K. 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 ).

2 1

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 4S°C. 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).

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, etc., 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 45°C. 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 of acetylacetone

with benzene and carbon tetrachloride. The higher positive values of Zt and rlE, and less

23

negative values of PEL and LEf of 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. Graph-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

disagreement with Jacobson's relation due to structural changes in these mixtures. This

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 30°C to 80°C. 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 Lagemm's relation d (s) does 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 decreae of space filling factor indicates

scope for more compression, and this leads to a decrease in ultrasonic velocity in higher

members of dicarboxylic acid series.

The 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

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 l°C 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 clathrate 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

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 55°C) from which the apparent molal volumes (g,) and

apparent molal adiabatic compressibility ($3 have been obtained. The results indicate that 4,

VS m'': and $, 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 aromatic acid salts. The $,' and $: values increase with

temperature for all the salts in the temperature range studied. The results were explained in

terms of solute-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.

30, 35, and 40°C. 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 calculated. The results indicate the possibility of formation of hydrogen

bonding of 0-H 0 type and C-H 0 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.

The ulhmsonic velocity and density of the solutions of phenol, a-napthol, and benzoic

acid in benzene and 1,4-dioxane were measured by Omchowski and Emst (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, dimethyl urea in the water-dioxane system by Misra 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 + bemne, n-hexane + acetone,

benzene + acetone at a frequency of 2 MHz 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 4S°C. A large number of acoustical and

thermodynamical properties, such as molar sound velocity, molar adiabatic compressibility,

29

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% aqueous 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

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).

31

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 MHz. Two and three chemical relaxation effects were observed

for 32 solutions of aluminium sulphate and scandium sulphate respectively, which are . consistent with a three step association mechanism. For scandium sulphate, rate and

equilibrium constants as well as volumes of reaction were obtained for all three reaction steps

by analysis of relaxation times and amplitudes.

Ultrasonic relaxational absorption was 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) have 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,

32

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 compressibil~ty and 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,), specifi~ ~ ~ ~ u u s t ~ c in~pcd~:: ; .

(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 Juszkiewicz (1989) by measuring the maximum velocity of

ultrasound in solutions of the following binaq solvents; water-ethanol, water-n-propanol,

33

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.) within 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

34

N-meth~lacetamide 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 on 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 aIP 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 of 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 30°C. These

35

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 amplitude 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 eta]., 1989).

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 al. (1986) measured ultrasonic velocity of the ternary system consisting

of water, 2-propanol and nitromethane at 35°C 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 25°C and the partial molar volume

37

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,.6H20 and La(N03),.6H,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- ions.

Ultrasonic velocities and densities at 30°C have been determined experimentally and

isentropic compressibility, intermolecular free length, molar sound velocity, specific acoustic

impedance, molal isentropic compressibility, 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 40°C by Nikam et al. (1991). The related

parameters were calculated. Bachem and Gucker's laws have been found to be valid.

Excess internal pressure of binary liquid mixtures of cuemene with

n-propan~l, and n-butan01 at 30, 35, and 40°C and ternary liquid mixtures of di~hloromethan~

with methanol + benzene, benzene + propanone, and methanol + proponone at 30°C 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 (THF) 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 THF. 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 30°C and

39

~H=3.5. The experimental results have been discussed on the basis of B j e r r ~ m ' ~ theory of

ion-association. The results of these chelates in water-dioxane mixture have been compared

with those obtained when water was used as 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) molecules 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.

(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 of electrolytes.

Four salts Et4NI, Pr,NI, BqNI and PehNI were examined by Pathak et al. (1992) in

formamide - DMSO from the point of view of apparent molal volume $, study by the

magnetic float densitometer method. The trend in t$ . and hence the nature of the slope 4, vs

c ' ' ~ curves 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

Ultrasonic velocity measurements were done in three ternary liquid mixtures of

toluene. benzene and 1-4dioxane with cyclohexane in chloroform. The isentropic

compressibility suggested the existence of specific molecular interactions between the

components of the mixtures (Kannappan et al., 1990).

1.5.4 BIOLOGICAL MOLECULES

Measurements of absorption and velocity of sound in blood, plasma and solutions of

albumin and haemoglobin 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 amino acids,

oligopeptides, and saccharides in aqueous solutions, and their dependence on the temperature

ha . been determined by the method of ultrasonic interferometry. The hydration of ionic.

hydrophilic and hydrophobic 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

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.

Sarvazyan 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 is due to a

43

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 changes 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 40°C. Adiabatic

compressibilities, apparent molal compressibilities, hydration numbers, and other related

parameters have been calculated. The temperature dependence of apparent mold

compressibility hints towards the partially independent contributions of positive and negative

parts of the glycine zwitterion.

Panial molar volumes of various species of six a-amino acids viz., as ~artic acid,

glutamic acid, lysine, arginine, alanine, and glycine were determined by Rao e. al. (1984) at

20°C from the pH-dependent density data of their aqueous solutions. In r ich system, the

amino acid species having the highest number of charges has the lowest par lal molar volume.

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 20°C: (i) glutamic acid : glycine; (ii) arginine : 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 are discussed in

terms of "specific interactions" between ionogenic side chains. The extent of interaction is

greater in systems 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

45

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 results

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 DNA, the concentration

0.07% to 0.08% seems to be important as 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 20°C and

at a frequency of 2 MHz. The results show that the velocity increment in the neutral aqueous

solution is larger because the amino 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

hanging pH. A 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. A new pulse

transmission technique has been used, which produces continuous absorption spectra for the

range 2-50 MHz, enabling accurate determination of relaxation frequency (f,) w~thin this

range. The variation of 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.