Indian Journal of ChemistryVol. 22A, December 1983, pp. 1029-1032

Viscosities & Electrical Conductivities of Solutions of Lithium Nitrate& Ammonium Nitrate in Dimethyl Sulphoxide

Z KODEJS·, J NOVAK & I SLAMAInstitute of Inorganic Chemistry, Czechoslovak Academy of Sciences, 16000 Prague 6, Czechoslovakia

Received 31 January 1983; revised and accepted 27 September 1983

The density, viscosity and electrical conductivity of highly concentrated solutions of lithium and ammonium nitrates indimethyl sulphoxide have been determined at 5" and 25°C and total salt concentration expressed in terins of mol fractions of0.2 and 0.33. The relative amounts of the two salts in solution are varied over the whole range between the pure components.The transport properties are compared for solutions of the two salts and for other systems. The properties of the ternary systemNH4NOrLiN03-DMSO are discussed as functions of the relative amounts of the two salts in the solution.

The intermediate range of concentration betweenanhydrous molten electrolytes and dilute electrolytesolutions is of interest to researchers from theoreticaland industrial view points. A number of papers dealingwith transport and volumetric properties of highlyconcentrated aqueous solutions, have appeared inrecent literature I -7, but the number of papers ontransport properties of highly concentrated solutionsof electrolytes in non-aqueous solvent, dimethylsulphoxide (DMSO) are limited" -10.

In previous studies we investigated transportproperties of highly concentrated solutions ofinorganic salts in water"·12 and in DMS013, with aview to correlating viscosities or conductivities of thesolutions with the structural parameters of solutes.Comparison of the transport properties was made withallowance for the properties of the two solvents used. Ithas been found that the difference in the behaviour ofaqueous and non-aqueous systems and the influence ofthe nature of solute become more marked as the saltconcentration in the system is increased. Of thesystems amenable to study by conventional methodsover wide concentration ranges, solutions ofammonium nitrate14 and lithium nitrate'? in DMSOhave been used for experimental investigation. Thischoice was not fortuitous. Results of previous studieshave indicated that it is the type of cation which has thedominating influence on transport properties ofsolutions. It was, therefore, of interest to study saltswith a common anion and different singly-chargedcations. The small, strongly polarizing lithium cationon one side, and equally symmetrical, but substantiallyless polarizing ammonium cation on the otherappeared particularly suitable for a comparativestudy .

. The aim of this work was to compare transportproperties of the above systems, and to investigate theproperties of the ternary system NH4N03-LiN03-

DMSO as functions of the relative amounts of the twosalts.

Materials and MethodsLiN03 (Merck, reagent grade) and NH4N03

(Merck, analytical grade) were vacuum-dried attemperatures under 120° and 90°C, respectively, andstored over phosphorus pentoxide. Dimethylsulphoxide (Merck, maximum water content 0.03%)was used as supplied.

Two sample sets were prepared for measurements,with total salt concentrations x = 0.2 and x = 0.33. Theionic fraction of lithium ion, y [= nLiNO)(nLiN03+nNH4NO~]was varied between 0 and I in steps of 0.1within each sample set. The samples were made up byweight. Densities, viscosities and electrical con-ductivities of the samples were determined at 5° and25°C, except for the samples that were not liquid underthe given conditions.

The density was determined by means of a DMA 40vibration densimeter (Paar) with a precision of ± 5x 10-4 gem -3; the viscosity by means of anUbbelohde capillary viscometer to within ± o.3%; andconductivity (to within ±O.I%) using a BM 484 semi-automatic bridge (Metra).

ResultsThe experimentally determined values of density (d),

viscosity (ry), and molar conductivity (1\) are presentedin Table I. The molar conductivities have beencalculated from measured specific conductivities X(Scm -I) and densities (gem -3), using the relation

... (I)

where MI, M2, and M3 are the molar masses ofDMSO, LiN03 and NH4N03, respectively, and x isthe mol fraction of the salts in solution.

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INDIAN 1. CHEM., VOL. 22A, DECEMBER 1983

Table I-Density, Viscosity and Molar Conductivity of Ternary System NH4NOrLiN03-DMSO at 5° and 25°C

y x d' '1' Aa r!' '1b Ab(gem -3) (mPa.s) (Scm/mot :") (gem -3) (mPa.s) (Scm2mol-')

0.0 0.333 1.2394 55.30 1.0671 1.2238 23.89 2.23930.0 0.200 1.1913 16.58 2.7538 1.1744 8.74 4.76150.1 0.333 1.2467 79.69 0.7628 1.2311 32.18 1.69100.1 0.200 1.1959 19.21 2.3130 1.1789 9.84 4.08060.2 0.333 1.2540 118.59 0.5368 1.2386 43.60 1.27000.2 0.200 1.2008 22.70 1.9351 1.1837 11.22 3.49320.3 0.333 1.2621 188.95 0.3502 1.2467 62.18 0.88830.3 0.200 1.2053 26.61 1.6116 1.1883 12.83 3.00030.4 0.333 1.2704 300.40 0.2260 1.2549 89.31 0.62600.4 0.200 1.2101 31.73 1.3168 1.1930 14.80 2.53000.5 0.333 1.2772 466.43 0.1437 1.2616 126.02 0.43550.5 0.200 1.2154 38.34 1.0605 1.1979 17.26 2.11470.6 0.333 1.2866 715.01 0.0981 1.2708 173.77 0.32200.6 0.200 1.2202 46.41 0.8497 1.2030 19.87 1.76920.7 0.333 1.2946 1056.8 0.0655 1.2784 233.27 0.23320.7 0.200 1.2252 54.68 0.6862 1.2076 22.63 1.48660.8 0.200 1.2304 67.01 0.5524 1.2128 26.01 1.25270.9 0.200 1.2354 79.56 0.4499 1.2174 29.40 1.06781.0 0.200 1.2404 93.00 0.3706 1.2220 32.91 0.9197

(a) At 5°C; and (b) at 25°C

For x =0.2 the properties investigated could bedetermined at both the temperatures over the wholeconcentration range 0 ~ y I, i.e. including both thebinary systems. The data obtained could, therefore, beused to express deviations of the properties of theternary system from the principle of their simpleadditivity. For x=0.33, only the interval 0:(y:(0.7was accessible experimentally, since samples with ahigher proportion of lithium nitrate could not bemaintained in the liquid state for the time required formeasurement.

DiscussionTransport properties of highly concentrated

solutions depend on ion-solvent interactions and totalstructure of solution. In comparing systems of nitrateswe must take into consideration differences betweencations. That the character of cation-solventinteractions is different for lithium and ammoniumions has been documented, e.g. by data obtained instudies of vapour pressures and molar volumes ofhighly concentrated aqueous16 -19 and DMS020.21

solutions of these salts. The calculated values of themolar enthalpy of evaporation of solvent (H20 orDMSO) from solutionl7.2o or the so-called net"adsorption" energy, defined as the molar energychange which occurs on transferring solvent from pureliquid solvent into molten LiN03 and NH4N03 givean indication of strong interactions between lithiumions and water or DMSO molecules in contrast toweak interactions between ammonium ions and wateror DMSO. The interactions of the two ions (lithium

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and ammonium) with DMSO molecules in highlyconcentrated solutions indicate that the ions formstronger "bond" with DMSO than do with water (for adetailed discussion see Ref. 20).

On these grounds we can now assess ourexperimental data, vis-a-vis data for calcium nitratesolutions in DMS013.

A comparison of viscosities and conductivities ofammonium nitrate and lithium nitrate solutions asfunctions of the salt concentration is shown in Fig. 1(curves a and b). The plot demonstrates that in contrastto the ammonium ion, the lithium ion has a profoundeffect on the solvent structure. The strong interactionof the lithium ion with DMSO molecules providing acompact structure results in a remarkable increase inthe viscosity ratio and a decrease in the conductivityratio with salt concentration. The concentrationdependences of viscosity and conductivity of highlyconcentrated solutions of LiN03, NH4N03 andCa(N03)2 are compared in Fig.2. Even though thelack of data on the behaviour of DMSO solutions ofother salts does not permit a generalization to be made,it is justifiable to conclude that the numerical viscosityvalues of solutions of the three ions are consistent withthe magnitudes of the polarizing effects of the ions onDMSO molecules. In the case of calcium nitrate, theeffect of the salt concentration in solution isstrengthened by the number of ions formed ondissociation of the salt.

There have been studies 'Y'" comparing theviscosities of aqueous and DMSO solutions ofammonium and lithium nitrates, but it is only the

15.0

•r10.0

5.0

KODEJS et al.: VISCOSITIES &: CONDUCTIVITIES OF LiNO) &: NH.NO) SOLUTIONS

.r------------------------------r~ow..:•

0.8•..

0.4

0.2

0.0'-- '-- '-- ---' 0.00.0 0.1 0.2

II

>'..•

••7S•IlLE..•..

f'""

100

so

1S

O~-- __L_ __ ~L_ __ ~ ~ ~O0.0 0.1 0.4 0." 0.. 1.0

y

Fig. 3-Viscosityofthe ternary system NH4NO)-LiN03-DMSO asa function of ionic composition (y) [e, 5', x =0.33; .•., 25" x =0.33;

0,5°, x=0.2; d, 25cC, x=0.2]

Fig. I-Ratio of transport properties ('1,or A,)as a function of thesalt concentration in solution at 25°C. [a-r)(LiN03-DMSO)/'1(NH4N03-DMSO); b--A(LiNO)-DMSO)/A(NH4NOrDMSO); c-r)(Ca(N03)2-DMSO)/r)(Ca(N03h-H20); d-r)(LiNOrDMSO)j'1(LiN03-H20); e-'1(NH4N03-DMSO)/'1(NH4NOr 4.0

H20)]

••...•-2.0

"•-4.0

s-.-2.0

1.0

0.0

-1.0•

- 6.0 '-- ......L. ...L- ~'-- -L- __ ..J -2.00.0 0.1 0.3 0.40.2

II

Fig. 2-Viscosity (IJ/pas) and conductivity (AjScm2mol-1) as afunction of composition at 25°C [a, dCa(N03)2-DMSO; b, e LiNOr

DMSO; c,/NH4NOrDMSO]

comparison shown in Fig. I (curves c-di that reveals aspecificity of the system LiN03-DMSO. While forsolutions in the mol ratio range 0.1 <x<0.18, theeffects of the solvent replacement are comparable forall the three salts, at higher concentrations the viscosityof the LiN03-DMSO system is substantially higherthan that of the aqueous solution. The interactions ofthe small lithium ion having a high surface chargedensity (z/r2, Li + : Ca 2 + : NH: =6.1 : 4.5 : 1) withDMSO molecules (dipole moment of DMSO is abouttwice that of water) is very strong. This may explain

"0E...·l.OE~

lit<,

< 2.0

1.0

0.0 L_-L_'--:C~~~_L-_....J0.0 0.2 0.6 0.8 1.00.4

y

Fig. 4-Conductivity of the ternary system NH4N03-LiNOrDMSO as a function of ionic compositon (Y), [e, 5'. x =0.33; .•.,25',

x=0.33; 0,5°, x=0.2; d, 25cC, x=0.2]

why the viscosity ratio for lithium nitrate solutionsstarts increasing steeply at such a salt concentration inthe system where virtually all solvent molecules arepresent in the first solvation spheres of lithium ions.

It was of interest to see how the different propertiesof the lithium and ammonium ions combine in theternary system, NH4N03-LiN03-DMSO. Figures 3and 4 show variations in the viscosity and conductivitywith the ionic composition of the system at differenttemperatures (5° and 25°C) and concentrations. Thevariations of the transport properties with temperatureand total salt concentration show trends similar tothose observed for other highly concentratedsolutions, and therefore will not be discussed.

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INDIAN J. CHEM., VOL. 22A, DECEMBER 1983

For x =0.2 both the transport properties could bestudied over the whole range of y from 0 to I, so thatone could evaluate deviations of the behaviour of theternary system from the additivity principle for theproperties of the two binary systems (LiN03-DMSOand NH4N03-DMSO). Both the transport propertiesstudied exhibit negative deviations from simpleadditivity rule.

For quantitative comparison of the magnitudes ofdeviations we have chosen the coordinate system (Wad

-WnpJ/IWLi-WNH41 versus y, where W denotes thetransport property (viscosity or conductivity) of theternary system, and WLi and WNH4 represent theproperties of the binary systems LiN03-DMSO andNH4N03-DMSO, respectively. The coordinatesystem has been chosen such that we can comparedeviations in conductivity and viscosity by means ofdimensionless quantities. The denominator IWLi-WNH41

implicitely expresses our assumption that themagnitude of the deviation depends on the differencein the behaviour of the two ions considered. The resultsare shown in Fig. 5. The plot shows no appreciabledifference between the two properties examined;maximum deviations occur at y = 0.5, and the plots aresymmetrical about this value independently oftemperature.

The negative deviations of viscosity may beexplained on the basis of the following consideration.The additivity rule is based on the concept of aweighted average of the properties of the two binarysystems. However, the ternary system does not involveany isolated regions with the structure of either of thebinary systems, and the two ions are statistically

I •0.2 f- • " •A••• A A• "A- 0 0 A

••• 0 e• A 0 0 "4 • A

0.1 - 0

" 0A ee !- 0

0

0.0 I I I I

0.0 0.2 0.• 0.6 0.8 1.0y

Fig. S-Deviations of viscosity and conductivity (dW) of the ternarysystem from additive behaviour as functions of ionic composition (y)andx=0.2. dW=(W.d·W••..>~WU·WNH41,wrepresents '1or 1\; viscosity:

e, 5°: 0, 25°; conductivity: &, 5°; 6, 25°C]

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distributed throughout the liquid phase volume. Thismeans that a small amount ofNH4N03 is sufficient todisturb the structure LiN03-DMSO. Conversely,addition of LiN03 to the system NH4N03-DMSOalso disturbs the structure NH4NOrDMSO, but theincrease in viscosity is not proportional to the addedamount ofLiN03 since the structure LiNOrDMSO,which is characterized by higher viscosity, cannot beformed.

The above reasoning cannot be invoked to explainthe negative deviations of conductivity, since theconductivity depends not only on the ioniccomposition and ionic mobility, but also on theviscosity of the system. Comparing the values of theproduct of conductivity and viscosity for the twobinary systems (0.046 Pa.s Scm -2mol -1 for NH4N03

and 0.034 Pa.s Scm+mol -1 for LiN03 at 5°C and x= 0.2), it is observed that the change in conductivity onchanging the ionic composition of the system is not dueonly to the change in viscosity, but arises also as aresult of a change in the mobility of ions in the electricfield. The mobility is, in turn, influenced by the changein the structure of the system.

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Electrochim Acta, 21 (1976) 997.2 Islam N &Ali A, Zphys Chem Leipzig, 263(1982) 365; 263(1982)

369.3 Islam N & Khan M M, Indian J Chem, 20 (1981) 1,7,9, 12.4 Jain S K & Tamamushi R, Can J Chem, 58 (1980) 1697.5 Islam N, Khan M M, Kumar S, Ahmad M & Pal Singh K, Indian

J Chem, 20 (1981) 1082.6 Islam N & Dhawan K, Indian J Chem, 20 (1981) 958.7 Gupta S, Sharma R C & Gaur H C, J chem Engng Data, 26(1981)

187, and references cited therein.8 Dunnet J S & Gasser R P H, Trans Faraday Soc, 61 (1965) 922.9 Butler J N, J electroanal Chem, 14 (1967) 89.

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