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
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.