chapter xi apparent molar volumes and viscosity b...

* Published in Journal of Chemical Thermodynamics 2010, 42, 380

CHAPTER -XI

Apparent Molar Volumes and Viscosity B-Coefficients of Caffeine

in Aqueous Thorium nitrate Solutions at

T = (298.15, 308.15 and 318.15) K

11. 1. Introduction

Alkaloids are a broad category of nitrogen containing organic metabolites

produced by plants. Of the three naturally occurring purine base xanthine alkaloids,

caffeine is the most significant stimulant to central nervous system 1. Pure caffeine

occurs as odourless, white, fleecy masses, glistening needles of powder. Its

molecular weight is 194.16 g, melting point is 236oC, pH is 6.9 (1% solution),

specific gravity is 1.2, volatility is 0.5%, vapour pressure is 760 mm Hg at 178oC,

solubility in water is 2.17 %, vapour density is 6.7 2. Caffeine- an additive to popular

carbonated drinks exists widely in the leaves, seeds, and fruits of a large number of

plants. Among them, cocoa beans, tea, coffee, cola, and guarana are the best known.

It has a wide range of effects on cardiovascular activity including vasoconstriction

and so forth 3. It produces acute elevations in both systolic and diastolic blood

pressure in most individuals [4] but as a complex forming agent decreases the

effective concentration of the anti-tumor antibiotic actinomycin D 5. It is teratogenic

and causes inhibition of DNA repair [6], inhibition cyclic AMP phosphodiesterase

activity 6 and inhibits seed germination. It can be a cause of cancer, heart diseases 7

and complications in pregnant women and ageing 8. It is a diuretic, has applications

in bilurubin determination in neonates with a clearing influence on the turbidity of

human sera 9. As drug it finds extensive applications in pharmacological

preparations including analgesics, diet aids, and cold/flu remedies 10. However, it

may produce confusion, tremours, insomenia and excitement leading to mild

delirium 1. Caffeine also finds applications as a chemical marker 11 in detecting

sources of domestic water pollution and as antioxidants 12. Thus, most of the studies

on caffeine relate to its physiological and pharmaceutical properties but studies on

Apparent Molar .................Thorium nitrate Solutions at T = (298.15, 318.15) K

294


its physicochemical properties in different solvent systems are still lacking. Only few

workers have studied self-association and thermodynamics of caffeine in aqueous

solutions. 13-16

Pyrimidine, purine bases and their derivatives are known to self-associate in

aqueous solution with the formation of dimer or higher aggregates by “vertical-

stacking” arising mainly due to optimization of Vander Waals contacts between

stacked molecules with planes apart at a distance of 3.4 Ǻ. Each step of such

associations is characterized by large negative enthalpy and entropy values 15. Again

caffeine is an interesting alkaloid with two different carbonyl groups- one isolated

and another conjugated; which are labeled as C=O(2) and C=O(6) in figure 1. Also

there are only few studies reported in the literature on the solution properties of

aqueous Th(NO3)4 solutions 17,18. Thus, in this paper we attempted to study the

various interactions in (0.00, 0.03, 0.05 and 0.07) 3dmmol −⋅ aqueous Th(NO3)4

solutions from solution density and viscosity measurements at temperatures in the

range (298.15 to 318.15) K as function of concentration of caffeine.

11. 2. Experimental

Caffeine was purchased from Loba Chemie, India, purity 99% and was

purified by dissolving it in aqueous ethanol and then recrystallized. Th(NO3)4.5H2O

was procured from Thomas Baker, India, purity 99% and was used without further

purification. Before using Th(NO3)4.5H2O was dried in vacuo for few hours. Triply

distilled, degassed water with a specific conductance <10-6 S.cm-1 was used for the

preparation of different aqueous Th(NO3)4 solutions. However, the concentrations

of Th(NO3)4 in different aqueous solutions were determined by EDTA titrations with

xylenol orange indicator 19 and necessary adjustments were done to have

approximately 0.03, 0.05 and 0.07 3dmmol −⋅ aqueous solutions of Th(NO3)4. The

physical properties of different aqueous Th(NO3)4 solutions are listed in table 1.

Table 1 shows that the experimental densities are in good agreement with the least

squares relations suggested by Apelblat et al 17. But we did not find any literature

viscosity data for our aqueous Th(NO3)4 solutions.


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Stock solutions of caffeine in different aqueous Th(NO3)4 solutions were

prepared by mass and the working solutions were prepared by mass dilution. The

conversion of molality into molarity was accomplished using experimental density

values. All solutions were prepared afresh before use. The uncertainty in molarity of

the caffeine solutions is evaluated to ± 0.0001 mol.dm-3.

The densities were measured with an Ostwald-Sprengel type pycnometer

having a bulb volume of 25 cm3 and an internal diameter of the capillary of about

0.1 cm. The pycnometer was calibrated at T = (298.15, 308.15 and 318.15) K with

doubly distilled water and benzene. The pycnometer with the test solution was

equilibrated in a water bath maintained at ± 0.01 K of the desired temperatures. The

pycnometer was then removed from the thermostatic bath, properly dried, and

weighed. Adequate precautions were taken to avoid evaporation losses during the

time of actual measurements. The mass measurements accurate to ± 0.01 mg were

made on a digital electronic analytical balance (Mettler, AG 285, Switzerland). The

total uncertainty in density was estimated to be ± 0.0001 g.cm-3 and that of the

temperature is ± 0.01 K.

The viscosity was measured by means of a suspended Ubbelohde type

viscometer thoroughly cleaned, dried and calibrated at T = (298.15, 308.15 and

318.15) K with triply distilled water and purified methanol. It was filled with

experimental liquid and placed vertically in a glass sided thermostat maintained

constant to ± 0.01 K. After attainment of thermal equilibrium, the efflux times of

flow of liquids were recorded with a stopwatch correct to ± 0.1s. In all

determinations, an average of triplicate measurements was taken into account.

Viscosity of solution, η, is given by the following equation:

)1()/( ρη tLKt−=

where K and Lare the viscometer constants and t and ρ are the efflux time of flow in

seconds and the density of the experimental liquid, respectively. The uncertainty in

viscosity measurements is within ± 0.003 mPa.s. Details of the methods and

techniques of density and viscosity measurements have been described elsewhere

20, 21. The experimental values of concentrations c, densities ρ, viscosities η, and


296


derived parameters at various temperatures are reported in table 2. The absorption

spectra of the studied solutions were recorded by Shimatzu (Japan) double beam

UV-VIS Spectrophotometer (model UV- 240) coupled with thermostatic

arrangement (model TB-85). The spectra of caffeine solutions in 0.03 3dmmol −⋅ aqueous Th(NO3)4 solutions were taken at the concentrations range from

5106.1 −× to 5100.5 −× 3dmmol −⋅ at ambient temperature using a quartz cell of 1 cm

path length. Double distilled water was used as the reference solvent throughout the

spectroscopic measurements.

11. 3. Results and discussion

For the analysis of solvation state of caffeine in aqueous Th(NO3)4 solutions

and the interaction between caffeine and Th(NO3)4, data of partial molar volumes

are important. For this purpose, the apparent molar volumes Vφ were determined

from the solution densities using the following equation 22:

)2()(1000 000 ρρρρφ cMV −−=

where M is the molar mass of the solute, c is the molarity of the solution, 0ρ and ρ

are the densities of the solvent and solution, respectively. As the plots of Vφ against

square root of molar concentration c , were linear, Vφ values were fitted to the

Masson equation 23:

)3(*0 cSVVV += φφ

where 0

Vφ is the partial molar volume at infinite dilution and *

VS the experimental

slope. The 0

Vφ values have been determined by fitting the dilute data (c < 0.1) to

equation (3) using least squares fit. The values of 0

Vφ and *

VS at each temperature are

reported in table 3. The estimated uncertainties in 0

Vφ , are equal to standard

deviation σ , the root mean square of the deviations between the experimental and

calculated Vφ for each data point. Our 0

Vφ value for aqueous caffeine solution at


297


298.15 K was in good agreement with the 0

Vφ value reported earlier 15. Table 3

shows that 0

Vφ values are generally positive and increase with a rise in the

temperature but decreases as the molarity of Th(NO3)4 in the mixtures increases.

However, 0

Vφ values of the aqueous Th(NO3)4 solutions are lower than those of the

binary solutions with caffeine. This indicates the presence of strong solute-solvent

interactions and these interactions are further strengthened at higher temperatures

but decreases as the molarity of Th(NO3)4 in the aqueous solutions increase from

0.03 to 0.07 3dmmol −⋅ .

Like other purine bases, caffeine in aqueous solution aggregate by plane-to-plane

staking 15, 24, 25. M. Falk et al 14 studied the self-association of caffeine in aqueous

solution by FT-IR spectroscopy showing absence of a single isobestic point; which

indicated the presence of more than two distinct molecular species in equilibrium

for aqueous caffeine solutions. A low concentration range of caffeine, 31025.0 −× to

3100.1 −× (M) the association is mainly between monomers. But at higher

concentrations, trimers and higher associations of caffeine are also present in

aqueous solutions. So we expect our caffeine solutions to have trimers and higher

aggregates in equilibrium. This fact justifies the observed decrease in apparent

molar volumes ( Vφ ) with increasing concentration for the studied caffeine solutions

at the experimental temperatures. The parameter, *

VS , is the volumetric virial

coefficient that characterizes the pairwise interaction of solvated species in solution

26-29. The sign of *

VS is determined by the interaction between the solute species. In

the present study *

VS values were found to be negative and decreases further as the

experimental temperature increases. This trend in *

VS values indicates weak solute-

solute interactions in the mixtures. But interestingly *

VS values increase as the

molarity of Th(NO3)4 in the studied mixtures increased; thus indicating increased

solute-cosolute interactions in the ternary mixtures.


298


The temperature dependence of partial molar volumes, 0

Vφ can be expressed

by the following relation:

)4(2

210

0 TaTaaV ++=φ

Values of the coefficients of the above relation for different caffeine solutions are

listed in table 4.

The partial molar expansibilities 0

Eφ can be obtained by the following equation 30:

( ) )5(2δδ 21

00 TaaTPVE +== φφ

The 0

Eφ values for different ternary solutions at 298.15, 308.15 and 318.15 K are

given in table 5. Table 5 reveals that 0

Eφ values decrease as the temperature

increases, except for aqueous caffeine solutions free of Th(NO3)4, and generally

increases as the molarity of Th(NO3)4 increases except for 0.07 mol.dm-3 of Th(NO3)4

solutions. This fact may be attributed to gradual disappearance of caging or packing

effect 31, 32 in the ternary solutions.

According to Hepler 33 the sign of ( )PE Tδδ 0φ is a good criterion in

characterizing the long-range structure-making and breaking ability of the solutes in

solution. The general thermodynamic expression used is as follows:

( ) ( ) )6(2δδδδ 2

2020 aTTPVPE == φφ

If the sign of ( )PE Tδδ 0φ is positive or small negative the solute is a structure maker,

otherwise it is a structure breaker. According to M. Falk et al 14 hydrogen bonding of

water to C=O groups of caffeine (figure 1) diminishes as the stacking of caffeine

molecules take place, i.e., stacking of caffeine releases hydrated water to the bulk

water. Thus caffeine acts as a water structure promoter. But this structure

promoting tendency of caffeine decreases when Th(NO3)4 is introduced in the

ternaries. Thus as evident from table 5, caffeine acts as a mild structure breaker

when Th(NO3)4 is introduced in the ternary solutions. Also, in aqueous Th(NO3)4

solutions, its structure breaking ability increases to some extent as the temperature

and the content of Th(NO3)4 in the experimental solutions increase. Such structure


299


breaking tendency of aqueous caffeine solutions has also been reported earlier by

W. E. Price et al 13.

Partial molar volumes 0

Vφ∆ of transfer from water to different aqueous

Th(NO3)4 solutions have been determined using the relations 34, 35:

)7(]Water[]solution)Th(NOAqueous[ 0

43

00

VVV φφφ −=∆

The 0

Vφ∆ value, by definition, is free from solute-solute interactions and therefore

provides information regarding solute-cosolute interactions 35. As can be seen from

table 6, the value of 0

Vφ∆ is generally positive at all the experimental temperatures

and decreases monotonically with the molarity of Th(NO3)4 in the ternary mixtures.

The concentration dependence of the thermodynamic properties of the solutes in

aqueous solutions can be explained in terms of overlap of hydration co-spheres.

According to the co-sphere model, as developed by Friedman and Krishnan 36, the

effect of overlap of the hydration co-spheres is destructive. The overlap of hydration

co-spheres of two ionic species results in an increase in volume but that of

hydration co-spheres of hydrophobic-hydrophobic groups and ion-hydrophobic

groups results in a net volume decrease. The positive values of 0

Vφ∆ indicate that

hydrophobic-hydrophobic and ion-hydrophobic group interactions are

predominant and the overall effect of the overlap of the hydration co-spheres of

caffeine and Th(NO3)4 reduce the effect of electrostriction of water by caffeine

molecules and this effect decreases with the molarity of Th(NO3)4 in the ternary

mixtures as shown in figure 2 ( 0

Vφ∆ versus molarity of Th(NO3)4 in aqueous

solutions).

Standard partial molar volumes, 0

Vφ of a solute can also be explained in terms

of a simple model 37, 38:

)8(0

SVoidVWV φφφφ −+=

where VWφ is the Vander Waals volume, Voidφ is the volume associated with voids or

empty space, and Sφ the shrinkage volume due to electrostriction. Assuming the


300


VWφ and Voidφ have the same magnitudes in water and in aqueous Th(NO3)4

solutions for the same solute 39, the increase in 0

Vφ values and the concomitant

positive 0

Vφ∆ values can be attributed to the decrease in the shrinkage volume of

water by caffeine in presence of Th(NO3)4. It is reported 14 that C=O groups of

monomeric caffeine molecules in aqueous solution can be assumed to be fully

hydrated; when vertical stacking takes place steric hindrance prevents full

hydration of C=O groups. But owing to the relative flexibilities of the dimer or

related associates the resulting dehydration effect is relatively small. The caffeine

molecules are, however, supported by a spine of water molecules in a hydrogen

bonded polymeric chain (unstable) as concluded from crystallographic investigation

40 and vacancies within these zig-zag hydrate chains allows a facile movement of the

water molecules 40. This facile movement of water molecules seems to increase

when Th(NO3)4 appears in the investigated ternaries. This fact, substantiated by the

extensive hydrolysis 41 of Th(NO3)4 in aqueous solution, suggests that Th(NO3)4 has

a dehydration effect on the hydrated caffeine. These results are also supported by

the UV-VIS absorption spectra of the studied solutions (figure 3). Due to the [Rn]0

electronic configuration of Th4+, it does not show any absorption but the aqueous

Th(NO3)4 solution shows maxλ at 298 nm due to −3NO ion, but when caffeine is

introduced this peak gradually disappears and forms a valley as the concentration of

caffeine increased in the solutions. Also due to the engagement of N9 of caffeine

molecule (figure 1) in hydrogen bonding in aqueous solutions lowering of intensity

as well as wavelength of *πn → transitions were observed. But with the advent of

Th(NO3)4 in the ternary solutions bathochromic shifts of the *πn → transition peaks

from 272–275 nm were observed, most probably due to extensive hydrolysis of

Th(NO3)4 in aqueous solutions.

It is reported 40 that in the crystal structure, caffeine molecules possesses a

hydrophobic center at the imidazole nitrogen atom, N9, (figure 1) susceptible to

hydrogen bonding and that the hydrated water molecule effloresces via a molecular

escape tunnel through the crystallographic a-face of the lattice (space group cP /21 ).


301


However, the various possible interactions between caffeine and Th(NO3)4 in water

can roughly be summarized as follows: (i) interaction of N9(caffeine) and Th4+ ion,

(ii) interaction of N9(caffeine) and H+ ion, (iii) interaction of C=O(2) and Th4+ ion,

(iv) interaction of C=O(6) and Th4+ ion, (v) interaction of C=O(2) and H+ ion , (vi)

interaction of C=O(6) and H+ ion, (vii) interaction of N1(caffeine) and −3NO ion, (viii)

interaction of N3(caffeine) and −3NO ion (ix) interaction of N7(caffeine) and −

3NO ion

etc., and (x) ionic-hydrophobic interactions between ions of Th(NO3)4 and non-polar

part of caffeine molecules. While interactions (i)-(ix) contribute positively,

interaction (x) contribute negatively to 0

Vφ values. Therefore the overall positive

0

Vφ values indicate that ionic-group interactions predominate over ionic-

hydrophobic interactions and thus reduce the electrostriction of water molecules by

caffeine imparting positive values of 0

Vφ .

The viscosity data of the aqueous and aqueous electrolytic solutions of

caffeine have been analyzed using the Jones-Dole [43] equation:

)9(110 cBAc)(ηc)ηη( r +=−=−

where 0ηηηr = , η0 and η are the viscosities of solvent and solution, respectively. A

and B are the parameters estimated by a least- squares method and reported in

table 7.

The viscosity B-coefficient 44 reflects the effects of solute-solvent interactions on the

solution viscosity. Table 7 illustrates that the values of the viscosity B-coefficient for

caffeine in the studied solvent systems are positive, thereby suggesting the presence

of strong solute-solvent interaction and these interactions are strengthened with a

rise in the experimental temperature but weakened as the molarity of Th(NO3)4

increases in the mixtures. However, the values of the A coefficient are either small

positive or negative for the experimental solutions indicating the presence of weak

solute-solute interactions, and their irregular behaviour may be due to the

hydrolysis of Th(NO3)4 in aqueous solutions 41.


302


Viscosity B-coefficients of transfer B∆ from water to different aqueous TBAB

solutions have been determined using the relations 34, 35-

)10(]Water[]solution)Th(NOAqueous[ 43 BBB −=∆

B∆ values shown in table 6 and depicted graphically in figure 2 ( B∆ versus molarity

of Th(NO3)4 in aqueous solution) as a function of molarity of Th(NO3)4 at the

experimental temperatures support the results obtained from 0

Vφ∆ values as

discussed earlier.

The viscosity data have also been analyzed on the basis of transition state theory of

relative viscosity as suggested by Feakings et. al 45 using the following equation: 0 0 0 0 0

2 1 2 1 1(1000 ) / (11)RT B∆µ ∆µ φ φ φ≠ ≠= + + −

where 0

1φ and 0

2φ are the partial molar volumes of the solvent and solute,

respectively. The contribution per mole of the solute to the free energy of activation

of viscous flow, ≠0

2∆µ of the solutions was determined from the above relation. The

free energy of activation of viscous flow for the pure solvent/solvent mixture, ≠0

1∆µ ,

is given by the relation: 45, 46 0 0 0

1 1 0 1∆ ∆ ln( ) (12)A

G RT hNµ η φ≠ ≠= =

where NA is the Avogadro’s number and the other symbols have their usual

significance. The values of the parameters ≠0

1∆µ and ≠0

2∆µ are reported in table 8.

Table 8 shows that ≠0

1∆µ is almost invariant of the solvent compositions and

temperatures, implying that ≠0

2∆µ is dependent mainly on the viscosity B-coefficients

and 0 0

, 2 ,1( )V Vφ φ− terms. But ≠0

2∆µ values were found to be positive at all the

experimental temperatures and this suggests that the process of viscous flow

becomes difficult as the temperature increase but becomes easier to some extent as

the molarity of Th(NO3)4 in ternary solutions increase. Hence the formation of the

transition state becomes less favourable 45. According to Feakings et. al 45 ≠0

2∆µ >

≠0

1∆µ for solutes having positive viscosity B-coefficients and indicates a stronger

solute-solvent interactions, thereby suggesting that the formation of transition state


303


is accompanied by the rupture and distortion of the intermolecular forces in solvent

structure 45. The greater the value of ≠0

2∆µ , the greater is the structure-making

tendency of a solute but the comparatively lower positive values of ≠0

2∆µ for caffeine

in the different aqueous Th(NO3)4 solutions than those in aqueous binary solutions

suggest caffeine to be a mild structure breaker in the studied ternaries. The entropy

of activation for electrolytic solutions has been calculated using the relation 45: 0 0

2 2d( ) d (13)S T∆ ∆µ≠ ≠= −

where ≠0

2S∆ has been obtained from the negative slope of the plots of ≠0

2∆µ against

T by using a least squares treatment.

The activation enthalpy ( ≠0

2H∆ ) has been calculated using the relation 45:

)14(0

2

0

2

0

2

≠≠≠ += ST∆µ∆H∆

The value of ≠0

2S∆ and ≠0

2H∆ are listed in table 8 and they were found to be negative

for all the experimental solutions and temperatures suggesting that the transition

state is associated with bond formation and increase in order. Although a detailed

mechanism for this cannot be easily advanced, it may be suggested that the slip-

plane is in the disordered state 45, 46.

11. 4. Conclusion

In summary, 0

Vφ and viscosity B-coefficient values for caffeine indicate the presence

of strong solute-solvent interactions and these interactions are further strengthened

at higher temperatures but decreases for higher molarity of Th(NO3)4 in the

ternaries. Also, caffeine acts as a mild structure breaker due to hydrophobic

hydration in presence of Th(NO3)4, which probably has a dehydration effect on the

hydrated caffeine.


304


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Table 1

Density ρ , and viscosity η of different aqueous Th(NO3)4 solutions at different

temperatures

Aqueous Th(NO3)4

solution )dm/(mol 3−⋅ T/K -3 310 /kg mρ −⋅ ⋅ s)/(mPa⋅η

0.03

298.15 1.0096 0.9090

308.15 1.0062 0.7386

318.15 1.0021 0.6158

0.05

298.15 1.0173 0.9329

308.15 1.0139 0.7558

318.15 1.0102 0.6234

0.07

298.15 1.0259 0.9457

308.15 1.0223 0.7672

318.15 1.0180 0.6452

Table 2

Molarity c, density ρ, viscosity η, apparent molar volume Vφ , and cr )1( −η for

caffeine in different aqueous Th(NO3)4 solutions at different temperatures

c

)dm/(mol 3−⋅ -3 310 /kg mρ −⋅ ⋅ s)/(mPa ⋅η 6 3 110 / m molVφ −⋅ ⋅ cr )1( −η

0.00 a

T = 298.15 K

0.0200 0.9981 0.893 143.34 0.0206

0.0320 0.9987 0.898 143.11 0.0477

0.0521 0.9998 0.905 142.92 0.0718

0.0721 1.0008 0.912 142.73 0.0903

0.0881 1.0016 0.919 142.60 0.1082

0.0999 1.0023 0.924 142.44 0.1194

T = 308.15 K


308


0.0199 0.9950 0.720 147.29 0.0059

0.0319 0.9956 0.723 147.07 0.0280

0.0519 0.9965 0.729 146.82 0.0586

0.0718 0.9975 0.735 146.58 0.0809

0.0877 0.9983 0.741 146.42 0.1014

0.0995 0.9989 0.745 146.29 0.1128

T = 318.15 K

0.0199 0.9912 0.600 149.70 0.0476

0.0318 0.9917 0.605 148.99 0.0847

0.0516 0.9927 0.614 148.05 0.1329

0.0715 0.9937 0.624 147.32 0.1757

0.0874 0.9945 0.633 146.82 0.2100

0.0991 0.9951 0.640 146.47 0.2345

0.03 a

T = 298.15 K

0.0200 1.0105 0.918 148.40 0.0700

0.0320 1.0111 0.923 147.00 0.0861

0.0520 1.0121 0.931 144.93 0.1061

0.0719 1.0132 0.940 142.80 0.1272

0.0879 1.0141 0.946 141.62 0.1373

0.0999 1.0148 0.952 141.00 0.1497

T = 308.15 K

0.0199 1.0070 0.746 153.26 0.0710

0.0319 1.0076 0.751 150.88 0.0940

0.0518 1.0086 0.759 147.68 0.1213

0.0717 1.0097 0.766 145.42 0.1385

0.0876 1.0106 0.772 143.76 0.1528

0.0996 1.0113 0.776 142.65 0.1604

T = 318.15 K

0.0198 1.0029 0.623 154.30 0.0831


309


0.0317 1.0034 0.627 152.10 0.1021

0.0516 1.0044 0.633 148.92 0.1230

0.0714 1.0055 0.640 146.64 0.1471

0.0873 1.0064 0.645 144.64 0.1605

0.0991 1.0071 0.650 143.42 0.1764

0.05 a

T = 298.15 K

0.0200 1.0184 0.938 139.86 0.0387

0.0319 1.0190 0.941 138.57 0.0486

0.0519 1.0202 0.948 136.95 0.0710

0.0719 1.0214 0.953 135.70 0.0803

0.0879 1.0223 0.957 134.80 0.0871

0.0999 1.0231 0.960 134.00 0.0919

T = 308.15 K

0.0199 1.0147 0.762 151.57 0.0581

0.0318 1.0152 0.765 150.30 0.0683

0.0517 1.0162 0.770 148.45 0.0826

0.0716 1.0171 0.776 147.05 0.0999

0.0875 1.0179 0.780 146.02 0.1082

0.0995 1.0186 0.783 145.43 0.1141

T = 318.15 K

0.0198 1.0109 0.631 156.29 0.0866

0.0317 1.0114 0.634 154.66 0.0955

0.0515 1.0122 0.640 152.80 0.1173

0.0713 1.0131 0.646 151.34 0.1358

0.0872 1.0139 0.650 150.20 0.1445

0.0991 1.0144 0.653 149.44 0.1508

0.07 a

T = 298.15 K

0.0200 1.0269 0.952 142.49 0.0471


310


0.0320 1.0275 0.956 142.45 0.0609

0.0520 1.0284 0.961 142.38 0.0709

0.0720 1.0294 0.967 142.31 0.0839

0.0880 1.0302 0.971 142.28 0.0902

0.1000 1.0308 0.975 142.25 0.0980

T = 308.15 K

0.0199 1.0231 0.772 149.44 0.0443

0.0319 1.0236 0.774 148.70 0.0496

0.0518 1.0245 0.779 147.75 0.0676

0.0717 1.0254 0.784 147.07 0.0818

0.0876 1.0262 0.787 146.52 0.0872

0.0996 1.0267 0.790 146.13 0.0942

T = 318.15 K

0.0198 1.0188 0.646 148.90 0.0088

0.0317 1.0194 0.647 147.66 0.0157

0.0516 1.0203 0.650 145.84 0.0327

0.0714 1.0214 0.654 144.36 0.0510

0.0873 1.0222 0.656 143.40 0.0566

0.0992 1.0228 0.659 142.66 0.0679

a = molarity of Th(NO3)4 in water in 3dmmol −⋅ .


311


Table 3

Limiting Partial Molar Volume 0

Vφ and experimental slope *

VS for caffeine in different

aqueous Th(NO3)4 solutions with standard deviations σ at different temperatures

T/K 0 6 3 110 / m molVφ −⋅ ⋅ * 6 9 3 1/210 / (m mol )VS−⋅ ⋅ σ

0.00 a

298.15 144.01 -4.86 0.001

308.15 148.09 -5.66 0.001

318.15 152.30 -18.58 0.001

0.03 a

298.15 154.71 -43.75 0.007

308.15 161.73 -60.79 0.006

318.15 163.16 -62.50 0.002

0.05 a

298.15 144.49 -32.97 0.003

308.15 156.60 -35.62 0.002

318.15 161.68 -38.89 0.001

0.07 a

298.15 142.69 -1.41 0.001

308.15 152.07 -18.79 0.001

318.15 154.01 -35.98 0.001

a = molarity of TBAB in water in 3dmmol −⋅ .

Table 4

Values of the Coefficients for equation (4) for caffeine in different aqueous Th(NO3)4

solutions

Aqueous Th(NO3)4

solution )dm/(mol 3−⋅

6

0 10⋅a /

13 molm −⋅

6

1 10⋅a /

-113 Kmolm ⋅⋅ −

6

2 10⋅a /

-213 Kmolm ⋅⋅ −

0.00 82.083 0.014 0.001

0.03 -2622.493 17.648 -0.028

0.05 -3445.989 22.522 -0.035

0.07 -3554.740 23.492 -0.037


312


Table 5

Limiting partial molar expansibility 0

Eφ for caffeine in different aqueous Th(NO3)4

solutions at different temperatures

Aqueous Th(NO3)4 solution

3dm/mol −⋅

0 610Eφ ⋅ / -113 Kmolm ⋅⋅ − 0

6δ10

δ

E

pT

φ ⋅

/ -213 Kmolm ⋅⋅ − 298.15 K 308.15 K 318.15 K

0.00 0.610 0.630 0.650 0.002 0.03 0.952 0.392 -0.168 -0.056 0.05 1.651 0.951 0.251 -0.070 0.07 1.429 0.689 -0.051 -0.074

Table 6

Partial molar volumes 0

Vφ and viscosity B-coefficients B∆ of transfer from water to

different aqueous Th(NO3)4 solutions for caffeine at different temperatures Aqueous Th(NO3)4 solution

)dm/(mol 3−⋅

0 6

3 1

10

/m mol

Vφ−

⋅

⋅

0 6

3 1

10

/m mol

V∆φ−

⋅

⋅

B 13 mol/m −⋅

B∆ /13 mol/m −⋅

T = 298.15 K

0.00 144.01 0.00 0.546 0.00 0.03 154.71 10.69 0.451 -0.095 0.05 144.49 0.47 0.313 -0.233 0.07 142.69 -1.33 0.279 -0.267 T = 308.15 K 0.00 148.09 0.00 0.613 0.00 0.03 161.73 13.64 0.510 -0.103 0.05 156.60 8.51 0.329 -0.284 0.07 152.07 3.98 0.298 -0.315 T = 318.15 K 0.00 152.30 0.00 1.067 0.00 0.03 163.16 10.86 0.522 -0.545 0.05 161.68 9.38 0.387 -0.680 0.07 154.01 1.71 0.344 -0.723


313


Table 7

Values of A and B-coefficients with standard errors for caffeine in different aqueous

Th(NO3)4 solutions at different temperatures

Aqueous

Th(NO3)4

solution

)dm/(mol 3−⋅

A 1/23/2 mol/m −⋅ B 13 mol/m −⋅

T =

298.15 K

T =

308.15

K

T =

318.15 K

T =

298.15 K

T =

308.15 K

T =

318.15 K

0.00 -0.054

(±0.003)

-0.081

(±0.008)

-0.106

(±0.001)

0.546

(±0.005)

0.613

(±0.002)

1.067

(±0.010)

0.03 0.005

(±0.003)

0.002

(±0.002)

0.008

(±0.005)

0.451

(±0.002)

0.510

(±0.006)

0.522

(±0.011)

0.05 -0.005

(±0.001)

0.010

(±0.001)

0.030

(±0.010)

0.313

(±0.001)

0.329

(±0.003)

0.387

(±0.018)

0.07 0.009

(±0.001)

-0.001

(±0.002)

-0.043

(±0.004)

0.279

(±0.006)

0.298

(±0.009)

0.344

(±0.010)

Standard errors are given the parenthesis.

Table 8

Values 0 0

,2 ,1( )V Vφ φ− , ≠0

1µ∆ , ≠0

2µ∆ , ≠∆ 0

2ST and ≠0

2∆H for caffeine in different aqueous

Th(NO3)4 solutions at different temperatures

Parameters 298.15 K 308.15 K 318.15 K

0.00 3dmmol −⋅

0 0 6 3 1

,2 ,1( ) 10 / m molV Vφ φ −− ⋅ ⋅ 125.86 129.88 133.92

)molkJ/( 10

1

−≠ ⋅∆µ 9.17 8.94 8.76

)molkJ/( 10

2

−≠ ⋅∆µ 100.92 113.47 181.60

)molkJ/( 10

2

−≠ ⋅∆ST -1202.72 -1243.06 -1283.40

)molkJ/( 10

2

−≠ ⋅∆H -1101.81 -1129.59 -1101.81


314


0.03 3dmmol −⋅

0 0 6 3 1

,2 ,1( ) 10 / m molV Vφ φ −− ⋅ ⋅ 136.77 143.64 144.90

)molkJ/( 10

1

−≠ ⋅∆µ 9.19 8.99 8.83

)molkJ/( 10

2

−≠ ⋅∆µ 90.47 101.58 105.43

)molkJ/( 10

2

−≠ ⋅∆ST -223.06 -230.54 -238.02

)molkJ/( 10

2

−≠ ⋅∆H -132.59 -128.96 -132.59

0.05 3dmmol −⋅

0 0 6 3 1

,2 ,1( ) 10 / m molV Vφ φ −− ⋅ ⋅ 126.60 138.55 143.56

)molkJ/( 10

1

−≠ ⋅∆µ 9.25 9.05 8.84

)molkJ/( 10

2

−≠ ⋅∆µ 70.16 75.41 86.31

)molkJ/( 10

2

−≠ ⋅∆ST -240.67 -248.74 -256.81

)molkJ/( 10

2

−≠ ⋅∆H -170.50 -173.32 -170.50

0.07 3dmmol −⋅

0 0 6 3 1

,2 ,1( ) 10 / m molV Vφ φ −− ⋅ ⋅ 124.85 134.17 135.94

)molkJ/( 10

1

−≠ ⋅∆µ 9.28 9.06 8.93

)molkJ/( 10

2

−≠ ⋅∆µ 65.40 70.92 79.16

)molkJ/( 10

2

−≠ ⋅∆ST -205.08 -211.96 -218.84

)molkJ/( 10

2

−≠ ⋅∆H -139.68 -144.05 -139.68


315


O N

CH3

N

CH3

N

N

H3C

O

1

23

4

56

7

8

9

Figure 1. Molecular structure of caffeine

-0.3

-0.2

-0.1

0.0

-0.3

-0.2

-0.1

0.0

-0.8

-0.6

-0.4

-0.2

0.0

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07

0

2

4

6

8

10

12

T = 318.15 K

φ V

0

Molarity of Th(NO3)

4 in aqueous solutions

-2

0

2

4

6

8

10

12

14

T = 308.15 K

φ V

0

-2

0

2

4

6

8

10

12

φ V

0

T = 298.15 K

∆B

∆B

∆B

Figure 2. Plots of partial molar volume ( 0

Vφ∆ ) and viscosity B-coefficient ( B∆ ) of

transfer from water to different aqueous Th(NO3)4 solutions for caffeine at

different temperatures. Solid lines for 0

Vφ∆ and dotted lines for B∆ , T = 298.15 K

(∆); T = 308.15 K (o); T = 318.15 K (g ).


316


260 280 300 320 340

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

6

5

4

3

21

Abs

λ (nm)

Figure 3. Changes in the UV-Visible absorption spectra of caffeine solutions: (1) 0.03 3dmmol −⋅ aqueous Th(NO3)4 solution, (2) 3-3 dmmol101.0 −⋅× aqueous caffeine

solution, (3) 5-3 dmmol101.6 −⋅× caffeine in solution 1, (4) 3-5 dmmol103.0 −⋅× caffeine

in solution 1, (5) 3-5 dmmol104.2 −⋅× caffeine in solution 1, (6) 3-5 dmmol105.0 −⋅×

caffeine in solution 1.

chapter xi apparent molar volumes and viscosity b...

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