CHAPTER IV

ULTRASONIC STUDIES ON THE INFLUENCE OF ELECTROLYTES ON MOLECULAR INTERACTIONS IN

AQUEOUS SOLUTIONS OF ETHYLENE GLYCOL

CHAPTER IV

ULTRASONIC STUDIES ON THE INFLUENCE OF

ELECTROLYTES ON MOLECULAR INTERACTIONS

IN AQUEOUS SOLUTIONS OF ETHYLENE GLYCOL

4.1 INTRODUCTION

Water, unlike many other liquids exhibits, anomalies in its physical properties as a

function of temperature. This peculiarity has been attributed to its hydrogen bonded

structure. When a solute. either electrolyte. or non-electrolyte, or both, is added to water.

I[ affects the structural equilibrium existing between hydrogen bonded clusters and

monomers. The possible structural changes are (a) stabilization of hydrogen bonded

clusters against thermal collapse, (b) promotions of long range order, (c) formation of

clathrate ljydrate like structures, or (d) collapse of the hydrogen bonded clusters.

The variation of ultrasonic velocity, adiabatic compressibility. and viscosity in

d~lute solutions containing electrolytes (or non-electrol)?es) with solute concentration

generally exhibits an extrema at some solute concentration (Kaulgud et al.. 1975; Atkinson et

a1. 1980; Burton, 1948; Endo et al., 1973; Hertz et a]., 1929). These extrema were attributed

10 the structural changes taking place in the solvent water, and these changes are generally

large due to the addition of the solute, which optimizes the structural changes at the solute

COncentrations whose extrema are observed. The ultrasonic studies in aqueous solutions of

non-electrol)?es indicate that non-electrolytes, which are soluble, are generally

,+,ater-structure promoters or breakers.

When an electrolyte is dissolved in water, it dissociates into anions and cations.

Aqueous electrolyte solutions are characterised by many peculiarities in their physical

properties, owing to the existence of ion-ion, ion-solvent. and solvent-solvent interactions.

Ethylene glycol-water mixture behaves like an elastomer, and the study of the

physical properties has attracted attention due to its glassy behaviour. A survey of the

available literature shows that considerable amount of data is available on the influence of

electrolytes on the structural aspects of ethylene glycol solutions (Blockra et al.. 1976). The

data on ultrasonic velocity and absorption studies in aqueous ethylene glycol solutions

containing CdSO,, CdC12, and Cdl is scanty. The electronic structure of cadmium is Is2, 2s2,

?ph. 3s2, 3p6, 3d1', 4s2, 4p6, 4dI0, 5s'. In this case, the 5s shell gets filled up leaving the 4f shell

empty. In rare earth elements (cerium to europium), the 4f shell gets progressively filled

up. and their salts are known to be either water structure-maker or breaker (Srinivasa Rao et

al., 1991). In order to find whether the absence of 4f shell of cadmium in cadmium salts cause

any change in the nature of interaction with aqueous solutions, the present study of ultrasonic

~elocity and absorption in the above solutions was undertaken

Ultrasonic velocity and absorption were measured in ethylene glycol-water mixtures

of volume proportions 10% ethylene glycol and 90% water (Solution A), 20% ethylene

~Iycol and 80% water (Solution B). and 30% ethylene glycol and 70% water (Solution C) at

a temperature of 303K. Electrolytes cadmium sulphate, cadmium iodide. and cadmium

69

chlor~de are added to the above solutions A, B, and C respectively to form the electrolyte

concentrations ranging from 0.01 to 0.1 molarity. The chemicals used were of ARIBDH

quality. Ethylene glycol is purified before use, and double distilled water is used in the

peparation of solutions A, B, and C. The ultrasonic velocity and absorption in these

solutions were measured at a temperature of 303K. using pulse echo interferometer

operating at a frequency of 10 MHz as described in Chapter 11. The densities of these

solutions were determined, using a specific gravity bottle of capacity 5 ml. The viscosity

or these solutions were determined using an Ostwald's viscometer. The temperature is

maintained constant throughout the experiment within =O.l°C. The ultrasonic parameters

such as adiabatic compressibility, intermolecular free length, excess absorption. volume

\iscosity, and relaxation time were calculated in these solutions in all the concentrations.

'The data on velocity, observed absorption, density, viscosity, intermolecular free length,

classical absorption, excess absorption, volume viscosity, and relaxation time of aqueous

ethllene glycol solutions with and without the electrolytes are given in tables 4.1 to 4.9.

The variation of ultrasonic velocity, adiabatic compressibility, intermolecular free length,

observed absorption, excess absolption, and volume viscosity with concentration are

graphically represented in figures 4.1 to 4.1 5.

1.2 RESULTS AND DISCUSSION

ULTRASONIC VELOCITY STUDIES

4.2.1 SYSTEMS OF ETHYLENE GLYCOL-WATER (WITHOUT ELECTROLYTES)

In aqueous solutions of ethylene glycol with ethylene glycol concentration vqving

from 10% to 30%, the ultrasonic velocity is found to increase with increase in the

concentration of ethylene glycol. The adiabatic compressibility decreases with increase in

the concentration of ethylene glycol in water (Tables 4.1 to 4.3). The observed non-linear

increase in ultrasonic velocity and decrease in adiabat~c compressibility with concentration

generally indicate some type of complex formation between the constituents of the mixture

(Notnoto, 1953). The increased cohesion be due to ionic hydration of the solutes

(Ramabramham. 1968). or due to hydrogen bonding between the solute and solvent

molecules. In the present case, the increased cohesion between the molecules in these

solutions is likely to be due to the later effect. The ethylene glycol is a dihydric alcohol

having two hydroxyl groups. whlch may form hydrogen (0-H..O) bonds with water

molecules. The solubility of alcohols is high in water because the oxygen atom of the

hydroxyl group in alcohols can form hydrogen bonds with water molecules (Soni. 3973).

The above conclusion appears to be similar to the one drawn by Rajagopalan et at. (1988)

from their ultrasonic studies in water-methanol mixtures at 0. 15. 25. 30, and 40°C. From

the variation of adiabatic compressibility. free volume, internal pressure, they concluded

the formation of aggregate termed as "methanol-aggregate" through H bonds between the

methanol and water molecules. In addition, panial molar volume and light scattering studies

7 1

In aqueous solutions of alcohols supports the above conclusion (Jumean. 1991; Grassman et

81.. 1981). This view is further confirmed by the study of refractive index in aqueous

srilutions of glycol (Douheret et al.. 1979).

4.2.2. AQUEOUS ETHYLENE GLYCOL W I T H CdSO,, CdCI,, AND C d I

The variation of ultrasonic velocity with the concentration of CdSO,. CdCI,, and CdI

In solutions .4. B, and C of ethylene glycol are shown in figures 4.1 to 4.3. It can be seen

from the figures 4.1 and 4.2 that in solution A at the temperature of 303K. the ultrasonic

\.elocity increases as the concentration of CdSO, and CdCI, is varied from 0.01 to 0.1

molarity. The ultrasonic velocity in solutions A, B, and C containing Cdl remains fairly

constant up to 0.3 molar electrolyte concentration. and then decreases slightly with increase

of electrolyte concentration (Fig. 4.3). A similar behaviour in ultrasonic velocity is observed

i\ith increasing concentrations of CdSO,, CdCI,. and Cdl in solutions B and C. The

ultrasonic velocity generally increases with the increase in concentrations of ethylene glycol

In water for a given CdSO,. CdCI,, and CdI concentration. It can further be seen that

the increase in the ultrasonic velocity is larger for solution containing CdSO,, as compared to

the solution containing CdCI,, or CdI for the same concentration of ethylene glycol.

Plots of adiabatic compressibility with concentration of CdSO,. CdCI:. and Cdl in

aqueous ethylene glycol mixture are shown in figures 4.1 to 4.3. The adiabat~c

compressibility decreases with the increase in the concentration of CdSO, and CdCI,.

For solutions containing Cdl. the adiabatic compressibility remains fairly constant In the

above range of electrolyte concentration. The variation of adiabatic compressibility for

72

5:s - - ULTRASONIC VELOCITY

C - 4 ADIABATIC COMPRESSIBILITY

CONCENTRATION IN MOLARITY ( X )

$ 4 . I . ULTRASONIC VELOCITY AND ADIABATIC COMPRESSIBILITY Vs. CONCENTRATION Of CADMIUM SULPHATE IN AQUEOUS

ETHYLENE GLYCOL

5.5 - U L T R A S O N I C VELOCITY I

*--@ ADIABATIC COMPRESSIBIL ITY

CONCENTRATION IN MOLARITY ( X )

u. ULTRASONIC VELOCITY AND ADIABATIC COMPRESSIEULITY Vs.CONCENTRATION OF CADMIUM CHLORIDE IN AQUEOUS

ETHYLENE GLYCOL

- ULTRASONIC VELOCITY

*-4 ADIABATIC COMPRESSIBILITY

CONCENTRATION IN MOLARITY ( X )

-3. ULTRASONIC VELOCITY AND ADIABATIC COMPRESSIBILITY Vs. CONCENTRATION OF CADMIUM IODIDE IN AQUEOUS ETHYLENE GLYCOL

,~lutions B and C with increasing concentration of cadmium salts are similar. The adiabatic

~~mpressibility decreases with the increase in concentration of ethylene glycol in water for a

ci\en electrolyte CdSO,, CdCI,, and Cdl concentration.

The variation of intermo;ecular free length in the solution with molarity of CdSO,.

CdCI,, and Cdl at 303K are shown in figures 4.4 to 4.6. The free length of the solution

decreases as the concentration of CdSO,, CdCl,, and CdI in solution A increases. A similar

hel~aviour in intermolecular free length is observed with increasing concentration of

C'dSO,, CdCI,, and CdI in solutions B and C . It can further be seen that the intermolecular

ircc length decreases with the increase in concentration of ethylene glycol in water for a

parricular CdSO,. CdCI,, and CdI concentration. The intermolecular free length is largest

for solutions containing Cdl, as compared to solutions containing CdCI, and CdSO, in all

aqueous solutions A, B, and C of ethylene glycol.

The hydration numbers of CdSO,, CdCI, and CdI in aqueous solutions A, 9. and C

oi'ethylene glycol solutions are shown in tables 4.1 to 4.9. The hydration number decreases

as the concentration of cadmium salts increases and reaches a constant value.

Relative association of solutions A, B, and C with increase of CdSO,, CdCI,, and

Cdl concentration are given in tables 4.1 to 4.9. It is seen that for all the three ethylene

gl!col solutions the relative association increases with the increase in CdSO,, CdCI,,

dnd Cdl concentration.

CONCENTRATION IN MOLARITY ( X )

E 4 . 4 . INTER- MOLECULAR FREE LENGTH H. CONCENTRATION OF CADMIUM SULPHATE IN AQUEOUS ETHYLENE GLYCOL

CONCENTRATION IN MOLARITY ( X )

FlG:4.5. INTER-MOLECULAR FREE LENGTH VS. CONCEN-

TRATION OF CADMIUM CHLORIDE IN AQUEOUS ETHYLENE GLYCOL

CONCENTRATION IN MOLARITY ( X )

5 4 . 6 . INTER- MOLECULAR FREE LENGTH Vs. CONCENTRATION OF CADMIUM lODlDE IN AQUEOUS ETHYLENE GLKOL

The salient features of this study are as follows:

1. The ultrasonic velocity in solutions A, B, and C of aqueous ethylene glycol

solut~ons increases w ~ t h the increase in CdSO, and CdCI, concentration. The

ultrasonic velocity in solutions A, B, and C containing Cdl remains fairly

constant up to 0.3 molar electrolyte concentrations, and then decreases slightly

with the increase of electrolyte concentration.

2. The ultrasonic velocity increases with the increase in ethylene glycol in water

for a given CdSO,, CdCI,, and CdI concentration.

3. The adiabatic compressibility for the above solutions decreases with the

increase in CdSO, and CdCI,. The adiabatic compressibility remains fairly

constant up to 0.3 molar electrolyte concentration, and then increases slightly

with increase of electrolyte concentration.

4. The intermolecular free length also has the same behaviour as that of the

adiabatic compressibility.

5. The hydration number decreases with increase in concentration of CdSO,,

CdCI,, and CdI in aqueous solutions of ethylene glycol.

6. The relative association in the solutions A, B, and C increases with increase in

concentration of CdSO,, CdCI,, and Cdl.

The ultrasonic velocity in the aqueous solutions of A, B, and C of ethylene glycol

Increases with the addition of electrolytes CdSO, and CdCI,. The increase in ultrasonic

\elocity in these solutions may be attributed to the cohesion, brought about by the ionic

74

h!dmtion. CdSO, and CdCI, is a strong electrolyte which dissolves in water to form Cd*',

50; and Cl' ions. The water molecules are attached to the ions strongly by electrostatic

forces. which introduce a greater cohesion in the solution. However, the increase in

ul~rasonic velocit~ on addition of CdSO, seems to be greater, as compared to CdCI, for

In! particular electrolyte concentration. (This result is in agreement with the ultrasonic

studies of Ramabrahmam (1968), Satyanaryanamurthy ( 1 964), Mallikharjuna Rao (1987) and

Jha (1986)). In the present case the increased cohesion between the molecules in the

solutions appears to be due to ionic hydration. The hydration number reported for S O , ion

15 6 and for Cl' is 1 (Mason, 1965). The ionic radii of SO; and C1 are 1.41 and 1.81A0

respectively ( Pauling. 1960). This indicates that SO,^ ions form more hydration in aqueous

ethjlene glycol solutions because of 1:s large charge density Ions with larger value of

charge density always disturb the prevailing short range ordering in aqueous solutions and

E r ~ r n ~ hydration. From the literature (Kavanau, l964), it can be seen that the relatively small

ions like SO; induces higher order in the water structure. The increase in structural order

of water may result in more cohesion, and hence leads to a decrease in adiabatic

compressibility. The decrease in adiabatic compressibility should result in an increase in the

ultrasonic velocity, and such an increase in solutions A, B, and C containing CdSO, has been

observed in the present studies. The increased cohesion observed in solutions A, B, and C

containing CdSO, concentration may also be attributed to sulphate ion. which may form

(0-H ..O) hydrogen bonds, and such a possibility does not exist in CdCI, solutions. From the

above study, it may be concluded CdSO, is a stronger structure-maker than CdCI, in aqueous

e1h)lene glycol solutions A, B, and C. The ultrasonic velocity decreases at higher

concentrations of CdI in solutions A, B, and C of aqueous ethylene (Fig. 4.3). Generally,

the velocity of ultrasonic waves increases with increasing salt concentrations. With some

salts involving heavy metal cations, the ultrasonic velocity decreases with concentration

(Mason. 1965). Salts of this type include uranyl chloride and nitrate (Balachandran, 1956).

strontium iodide (Balachandran, 1956). lead acetate (Balachandran 1956) and nitrate

(Suhramanyan and Bhimanschachar, 1960) and cadmium bromide and iodide (Padmin~ and

Kao. 1960). The hydration number reported for 1. is 0. The ionic radius is 2.20A0. Since

lhc charge density of the iodide is low compared to with that for other Ions, the assumption

often made is that the electrostatic effects of the iodide ion on the surrounding water

tnolecules are negligible, and hence, that the hydration of this ion can be assumed to be zero

(Mason, 1965). Since the charge density is very small, the ions increase the fluidity of water

(Kabanau, 1964) in its immediate vicinity resulting in the weakening of molecular

interactions. This may be the reason for the observed decrease In ultrasonic velocity at

higher electrolyte concentrations

The variation of adiabatic compressibility in solutions A, B, and C containing

electrolytes CdSO,, CdCI,, and CdI generally supports the above conclusion.

The primary hydration numbers of CdSO,, CdCI,, and Cdl solutions A. B. and C of

aqueous ethylene glycol decrease with the increase in the concentration of electrolytes

(Tables 4.1 to 4.9). The primary hydration number decreases as the concentration of

76

ethbiene glycol in water increases for a given electrolyte concentration. A probable

e~planation may be given as follows: Considering flickering-cluster model of water and

the nlodel for hydration. Flickering cluster model of Frank and Wen (1957) postulate that

~ h c formation of hydrogen bonds in liquid-water is predominantly a co-operative

phenomenon. The existence of a pair of hydrogen-bonded atoms promotes the tendency of

sach atom to hydrogen bond to another neighbour. This results in the format~on of short

Ined flickering clusters of varying extent. consisting of highly hydrogen bonded molecules.

'Illese clusters are mixed with non-hydrogen bonded molecules (water monomers) about one

or two layers between them. Solutes like ethylene glycol which have hydroxyl gro13n-.

cnwr the cavities in the water structure. and increase the stabilization by forming

hhdrogen bond with the Hater molecule. This process may take up a few water monomers

also. The strong electrolytes like CdSO,. CdCI,. and CdI break up into ions due to the

large dielectric constant of water. The ions, in turn, attack the dipoles of water, and

strongly polarise and orient them by strong electrostatic force. The water monomers

surrounding the ions in the immediate vicinity are termed as primary hydration (Kavanau.

1964). They also induce additional order beyond the first water layer which is known as

Tccondary hydration or long range hydration (Bockris. 1949). The ethylene glycol

solutions stabilise the water structure probably through hydrogen bonding networks and a

few water monomers are left. The CdSO,, CdCI,, and CdI, dissolved in the aqueous

ethylene glycol solutions. are likely to be hydrated by the water monomers. When the

-oncentration of the CdSO,. CdCI,, and CdI is increased, the primary and secondw

11)dration molecules are redistributed and result in a smaller primary hydration number.

As the ethylene glycol concentration is increased from 10% to 309.6 in water. the

Ih!dration number decreases. At a higher ethylene glycol concentration. the number of free

mter n?onomers may be less, or more monomers are attached to the ethylene glycol

molecules. The dissolved CdSO,. CdCI,, and CdI find lesser number of free water

monomers to be distributed in pr imay and secondary shells.

It can be seen from the tables 4.1 to 4.9 that for the ethylene glycol solutions of all

concentrations. the hydration number of CdSO, is greater as compared to CdCI: and Cdl.

Th~s may be due to the higher charge density of sulphate ion. For all the ethylene gljcol

solut~ons, the hydration numbers of CdI are In genera1 relat~\,ely small as compared to the

hydration numbers of CdSO, or CdCI, which may be due to the smaller ionic radius of SO,"

and C1' in comparison with 1.. (The ionic radii of SO;.. CI-, and 1- are 1.41, 1.81, and 2.20A0

respectively) (Pauling, 1960).

The relative association ofsolutlons A, 13, and C of aqueous ethylene glycol solutions

increase with the concentration of CdSO,. CdCI,, and Cdl. For a given concentration of

electrolytes. the relative association increases for solution A. B, and C of aqueous ethylene

glycol. Relative association is influenced by two factors: ( I ) the breaking up of the solbent

molecules on addition of electrolyte to 11; and ( 2 ) the solvation of Ions that are

simultaneously present. The former resulting in a decrease and the latter in an increase of

relative association. In the present investigation. relative association increases w ~ t h

78

L~ncentration. The increase of relative association suggests that solvation of ions

over the breaking up of the solvent aggregates (ethylene glycol-water) on

~ j d ~ ~ ~ o n of CdSO,. CdCI,, and CdI.

1.3 ABSORPTION STUDIES

From the present ultrasonic velocity studies, it can be seen that the ultrasonic

islocitles in lo%, 20%, and 30% (solutions A, B, and C) aqueous ethylene glycol solutions

of CdSO,. CdCI,, and CdI change nonlinearly with increase in solute concentrations. In order

to understand the molecular dynamics completely, the parameters like structural viscos~ty

and ultrasonic relaxation time are also to be evaluated. The ultrasonic absorption studies

nil1 he more useful in elucidating these parameters. which may help further to understand the

nature of solute-sohent interactions in these systems.

The absorption measurements were carried out in this laboratory using pulse

echo Interferometer of frequency 10 MHz.

The solutions were prepared with the solute concentrations fo1lowi:lg the

procedure already reported in velocity studies. The ultrasonic absorption are measured, as

.ictatied in chapter I1 at room temperature (303K). Viscosities and densities of these

solutions were also determined, as explained earlier. Using the values of ultrasound

absorption, shear viscosity, and density of the solutions, the derived parameters are

calculated, as detailed below.

The classical absorption is calculated using the relation (I .I 9). The excess

dbsorption is estimated as the difference between the observed absorption and classical

79

,i.sorption. Volume viscosity, which is due to the structure of the liquid, is calculated using

illr relation ( I .22).

The variation of ultrasonic absorption and the calculated parameters with

o(,ncentration of electrolytes are shown In tables 4.1 to 4.9. The variation of observed

~hsorption. excess absorption. and volume viscosity with the solute concentration at a

tsniperature of 303K are shown graphically in figures 4.7 to 4.15.

The plots of observed absorption bersus CdSO,. CdCI,. and CdI concentration for

solutions A. B, and C of aqueous ethylene glycol solutions are shown in figures 4.7 to 4.9. I t

can be seen from the figures that the ultrasonic absorption increases with the increase in

elhylene glycol concentration in water without the addition of salts. It can also be seen

from the figure that the ultrasonic absorption in solutions A, B, and C of aqueous ethylene

gl)col solution increases with the increase of the concentration of CdSO,, CdCI,, and Cdl.

The magnitude of absorption IS found to be greater in solutions containing 20% and 30%

ethylene glycol for a given electrolyte ci~ncentration. The ultrasonic absorption is greater

h r CdI than for CdCI, and CdSO, in solut~ons A, B, and C.

The variation of excess absorption with concentration of CdSO,, CdCI,, and Cdl are

s h o w in figures 4.10 to 4.12. From these figures, it is observed that the excess absorption

has the same trend as that of the observed absorption. The variation of volume viscosity for

these electrolytes is shown in figures 4.13 to 4.15. The variation of relaxation time with

Concentration of electrolytes is shown in tables 4.1 to 4.9. The vartation of \olume viscus~ty

CONCENTRATION IN MOLARITY ( X )

FIG. 4.7. OBSERVED ABSORPTION VS. CONCENTRATION OF --

CADMllM SULPHATE IN AQUEOUS ETHYLENE GLYCOL

CONCENTRATION IN MOLARITY ( X I

CG-4.8. OBSERVED ABSORPTION VS. CONCENTRATION O F

FADMIUM CHLORIDE IN AQUEOUS ETHYLENE GLYCOL

CONCENTRATION IN MOLARITY ( X )

RG.4- 9. OBSERVED ABSORPTION VS. CONCENTRATION OF CADMIUM IODIDE IN AQUEOUS ETHYLENE GLYCOL

1 8 2 I I I I

0 0.02 0.01, 0.06 0.08 0.10

CONCENTRATION IN MOLARITY ( X )

-0. EXCESS ABSORPTION Vs. CONCENTRATION OF CADMIUM SULPHATE IN AQUEOUS ETHYLENE GLYCOL

180 1 I I I I 0.02 0.04 0.06 0.08 0.

CONCENTRATION IN MOLARITY ( X )

FIG:4.11 EXCESS ABSORPTION VS. CONCENTRATION OF - CADMWM CHLORIDE IN AQUEOUS ETHYLENE GLYCOL

CONCENTRATION I N MOLARITY ( X

FIG.4.12. EXCESS ABSORPTION Vs. CONCENTRATION OF - CADMIUM IODIDE IN AQUEOUS ETHYLENE GLYCOL

31 L I I 1 I

0 0.02 0.04 0.06 0.08 0 .lo

CONCENTRATION IN MOLARITY ( X

-3. VOLUME VISCOSITY Vs. CONCENTRATION OF CADMIUM SULPHATE IN AQUEOUS ETHYLENE GLYCOL

CONCENTRATION IN MOLARITY ( X )

%.4.14. VOLUME VISCOSITY VS. CONCENTRATION OF CADMIUM CHLORIDE IN AQUEOUS ETHYLENE GLYCOL

CONCENTRATION IN MOLARITY ( X )

~ . I S . V O L U M E VISCOSITY VS.CONCENTRATION OF CADMIUM

IODIDE IN AQUEOUS ETHYLENE GLYCOL

jnd relaxation time follows the same trend as that of observed absorption for these

sicctrolytes in aqueous ethylene glycol solutions.

The salient features of the absorption study are summarised as follows:

1. The ultrasonic absorption in solutions A, B, and C of aqueous ethylene glycol

solutions increases with the increase in ethylene glycol concentration.

2. The ultrasonic absorption in all aqueous solutions of ethylene glycol increases

with increase in CdSO,, CdCI,, and Cdl concentration in the range studied.

3. The excess absorption has similar behaviour as that of observed absorption.

4. Volume viscosit! and relaxation time are found to be increas~ng in 10%. 20%.

and 30% aqueous ethylene glycol solutions with the addition of CdSO,, CdCl?.

and Cdl.

The ultrasonic absorption in aqueous solutions of ethylene glycol generally increases

n ~ t h the increase in the concentration of ethylene glycol. The earlier measurements of

ultrasonic velocity in these solutions s h o ~ that the velocity increases with the increase in

ethylene glycol concentration. The increase in velocity has been attributed to the formation

of hydrogen bonds between the molecules of ethylene glycol and water. As the ultrasonic

naves pass through the medium, part of the energy is utilised in the weakening or breaking

up of 0 4 . 0 bonds. This explanation finds some support from the NMR studies of

Lippincon et al. (1964) that the hydrogen bonds tend to weaken when the protons are brought

cluser. So it is likely that during the compression cycle of the ultrasonic wave. hydrogen

atoms are pushed closer resulting in a partially irreversible weakening, or breaking of

81

h!drogen bonds due to the absorption of ultrasonic energy. As the pressure wave passes

through the medium completely, hydrogen bonds form again between molecules of ethylene

~ ~ z o l and water. Such type of making and breaking of intermolecular bonds probably

cuplains the observed phenomenon. S~nce the ethylene glycol molecules have two hydroxyl

i ~ f i ) groups, the number of the OH groups will increase as the ethylene glycol

concentration is increased. The large number of OH groups will lead to an increased

number of intra and intermolecular bonds. As the pressure wave passes. more energy has to

he utilised to break the larger number of intermolecular hydrogen bonds due to the

l~~crcase of concentration of ethylene glycol. This probably explains the observed increase

In absorption, as the ethylene glycol concentration is increased.

The variation of observed absorption as a function of concentration of CdSO,,

CdCI,, and Cdl in solutions A. B, and C of aqueous ethylene glycol is shown in figures 4.7 to

1 9 . It can be seen from these figures that the ultrasonic absorption increases with

~ncreasing concentration of CdSO,, CdCI,, and Cdl. The variation of excess absorption, as a

function of concentration of electrolytes, may be explained as follows

1. The ions act as acceptors and they can compete with the protons for the lone pair

of electrons on the oxygen

2. The ions may possess a large volume and hence a small effective charge density.

The equilibrium between the hydrogen bonded (A) and non-hydrogen bonded (B) structural

hrms is disturbed. Both these effects are likely to contribute to a change in the acoustic

absorption. The experimental \'slues (Tables 4.1 to 4.9) show a considerable excess

82

,hsorption over the classical values. The excess absorption in these solutions may be due

lo structural relaxations in these solutions. The periodic pressure changes associated with the

passage of ultrasonic waves disturbs the equilibrium of molecules in states (A) and (B). Since

.I fin~te time is involved in the trans~tion, the process involves relaxation causing structural

:ibhorprion.

In the present investigation, the ultrasonic absorption and excess absorption in all

rhe systems is found to increase with increase of elect~u~!.te concentration . This is siinilar to

tlir observation of Snlith el al. (1951) in aqueous solutions of MgS04. This may be

~rtrihuted to the fact that the electrostatic fields of 1 . C1-, an1 '0;. ions produce long range

order of the solvent molecules. As a result, the mobility of the solvent molecules closest to

Ions should a 1 a . a ~ ~ be less than the mobility of the molecules in pure solvent, ihis

tnakes the solutions more structured and hence thL ultrasonic absorption increases in the

iolutions.

Further the absorption of solution containing CdI is somewhat greater than that of

CdCI, and CdSO,. This can be understood by considering the fact that the bulk viscosity,

caused due to mismatch in phase between the stress variations of the compressional wave in

Ihe solution and the strain variation in the solution being greater in the solutions of Cdl than

lhose of other solutions due to its higher molecular weight. Shis result is in conformity with

the results of Kutze and Tamm (1953).

ULTRASONIC VELOCITY, ABSORPTION, AND RELATED PARAMETERS OF CADMIUM SULPHATE IN 10% AQUEOUS ETHY1,ENE GLYCOL

x c p q s x ~ 0 3 p , x ~ o " Lr 11 R.A. x1015 N ~ ~ K ' S ~ qv 10'

mol dmJ ms-' Kgm Nsm-2 N-'m2 A' ~ s m . ~ s

X - Concentration in molarity; C - Ultrasonic velocity; p -Density; rls - Shear viscosity; a - Adiabatic compressibility;

Lr - lnterrnolecular free length; h - Hydration numher; R.A. - Relative association; Ohsewed absorption;

(a/i)cl - Classical absorption; ju/'?) - Excess absorption; q v - Volume viscosity: TS - Relaxation timr. C Y

TABLE 4.2

ULTRASONIC VELOCITY, ABSORPTION, AND RELATED PARAMETERS OF CADMIUM SULPHATE IN 20% AQUEOUS ETHYLENE G1,YCOL

x c lo3 1o1O LI h R.A. ~ 1 0 ' ' N ~ ~ - ' S ~ qv 10' 10"

rnnl dm" Ins-' ~ ~ m - ~ ~ s m - ~ N.'rn2 A0 (")oh ( W)cl

~ s m . ~ s

X - Concentration in molarity; C - Ultrawnic velocity; p - Density; qs -Shear viscosity; - Adiabatic compressibility;

Lr- lnterrnolecular free length; h - Hydration number; R.A. - Relative association; Observed absorption;

('!/,i)cl - Clas5ical ahsorrption: ('%l)cl)er - Excess absorption; q v - Vulun~e viscosity; rs - Relaxation lime.

TABLE 4.3

ULTRASONIC VELOCITY, ABSORt'TION, AND RELATED PARAMETERS OF CADMIUM SULPHATE IN 30% AQUEOUS ETHYLENE GLYCOL

x c p qs lo3 , IO'O L, h R.A. ~ 1 0 ' ~ N ~ ~ - ' S ' r(v lo3 lo1'

mol dmJ ms.' ~~m~ Nsm.' ~ - ' m ~ A' ( a q c l (a'')CX

~ s m - ' s

X - Concentration in molarity; C - Ultrasonic velocity; p - Density: 115 - S h n ~ r viscosity; - Adiabatic compressibility;

Lf - Interml~lecular free length; h - Hydration number; R.A. - Relative assnciation; ('W)c,b - Oberved ahsorption;

(%i)<, - Classi~?l ahsorption; - Excess absorption; 11,' - Volume viscosity: TS - Relaxatiirn time.

ULTRASONIC VELOCITY, ABSORPTION, AND RELATED PARAMETERS OF CADMIUM CHLORlDE IN 10% AQUEOUS ETHYLENE GLYCOL

x c vs 103 ~5 lot0 L~ h R.A. ~ 1 0 ' ~ ~ ~ m - l s ' qv lo3 rs 10"

mol dmJ ms-I ~ ~ m - ~ Nsm-Z N-'m2 A'

X - Concentration in molarlty; C - Ultrasonic velocity; p - Density; qs -Shear viscosity; - Adiabatic compressibility;

LC- Intermolecular free length; h - Hydration number: R.A. - Relative associalion; - Ohserved absorption:

('!@)c, - Clasrical ahsti~ption: ('X)rr - Excess absorption; q v - Volume viscosity; rs - Relaxation time.

TARLE 4.6

ULTRASONIC VELOCITY, ABSORITION, AND RELATED PARAMETERS OF CADMIUM CHLORIDE IN 30% AQUEOUS ETHYLENE GLYCOL

x c p qc x id fi5 X 10" LI h R.A. *lo'5 N ~ ~ - ' s ~ qv 103 ts i n t1

mol dm-? ms-' ~ ~ m - ~ Nsm-2 N-1m2 A' ("/')oh ( a/')cl Nsm.' s

X - Concentration In molarity: C - Ultrasonic velocity; p - Density; qa - Shear v~sa)\ity: - Adiahntic compressibility;

Lr- Intermolecular free length; h - Hydration number; R.A. - Relative association: ( ' 7 1 ) ~ ~ - Ohserved absorption;

('Yi)', - Classical ahsorpllon; ('yi)cx - Excess ahsorptiun; q v - Volume viscosity; rs - Relaxation time.

TABLE 4.7

ULTRASONIC VELOCITY, ABSORITION, AND RELATED YARAME'TERS OF CADMIUM IODIDE IN 10% AQUEOUS ETHYLENE GLYCOL

x c I)s lo3 (j\ x loL0 LI h R.A. X I O I ~ ~ ~ m - l s ' qv lo3 rs lo t1 mol dm-3 ms-' Kgm Nsm-2 wlm2 A'

( ( u'')cl ( a'')cx NsniZ s

X - Concentration in rnolarity; C - Ultrasonic velocity; p - Density; 11s - Shear viscosity; - Adiahalic a~mpressibility;

1.r- Intermolecular free length: h - Hydration numhcr; R.A. - Relative association; - Ohserved absorption;

('l/?),, - Clars~cal absorption; ('l/i)tx - Excess ahsorpt~on; q v - Volume v~!,cosity; TS - Relaxat~on lime.

TABLE 4.8

ULTRASONIC VELOCITY, ABSORITION, AND RELATED PARAMETERS OF CADMIUM IODIDE IN 20% AQUEOUS ETHYLENE GLYCOL

x c p q s X 1 0 3 li ,xlolo ~f h R.A. ~ 1 0 ' ~ N ~ ~ - ~ s ~ rlv 10' ts 10"

mol dm-3 rns-' ~ ~ m - ~ Nsm-Z i--lm2 A' ( ( (O'')er Nsm-' s

X - Concentration in rnolar~ly; C - Ultrasonic velocity; p - Density; qs - Shear vlsa,sity; li, -Adiabatic compressibility;

L t lnlermolrcular free length; h - Hydration numher; R.A. - Relative aa\oclatinn; (a/?),,l, - Ohserved ahwrption;

( ' ~ I ) ~ , - Classical absorption: ("/i')cy - Excess ahsorptlon; I ) V - Volume viscosity; b -Relaxation time.

TABLE 4.9

ULTRASONIC VELOCITY, ABSORlTION, AND RELATED PARAMETEUS OF CADMIUM IODIDE IN 30% AQUEOUS ETHYLENE GLYCOL

x c p x I 0' ps x 10"' Lr h R.A. X I O ' ~ ~ ~ m - ~ s ~ rlv 103 Ts 10"

mol dm-' ms-I ~~m~~ ~sm. ' N.'m2 A' ~ s m - ' s

X - Concentrat~on in molarity; C - Ultrason~c velocity; p - Density; rls -Shear v~sc~~s i t y ; fk Adiabat ic compressibility;

Lr - lnlermolecular free length, h - Hydration numher; R.A. - Relat~ve assriciat~~in; (o/i'),,,, - Ohserved ahairption;

- Classical absorption; ("/i)cx - Excess absorption: rlv - Volume v~scosity; TS - Relaxation time.