Study the effect of ethanol on the conductivity of Potassium Nitrate at different...

Modern Trends in Science and Technology

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STUDY OF THE EFFECT OF ETHANOL ON THECONDUCTIVITY OF POTASSIUM NITRATE ATDIFFERENT TEMPERATURES

Nabin Basnet1, Ratna Bahadur Thapa1, Rajendra Dhakal1, DilliRam Pokharel1, Sujit Kumar Shah2 and Ajaya Bhattarai2*

1Department of Chemistry, Damak Multiple Campus, Damak, Nepal2Department of Chemistry, Mahendra Morang Adarsh Multiple CampusTribhuvan University, Biratnagar, Nepal

*E-mail: [email protected]

AbstractPrecise measurements on the conductivity of Potassium nitrate in pure water andethanol-water mixed solvent media containing 0.10, 0.20, 0.30, 0.40, 0.50, 0.60 and0.70 volume fractions of ethanol at temperatures 303.15, 308.15 and 313.15 K arereported. The concentrations were varied from ~ 0.010 to ~ 0.10 mol.L-1. The resultsshowed a sharp increase in the conductivity with increasing electrolyte concentration.The increase in the conductance with concentration is due to an increase in number ofions per unit volume of the solution. The decrease in conductivity with increase in theamount of ethanol is due to the reduction of relative permittivity of the ethanol-watermixed solvent phase and makes easier for the formation of ion-pairs in the solutionphase.

Key words: Mixed solvent media, conductivity, potassium nitrate, ethanol

IntroductionElectrical conductivity is one of the principle transport properties ofaqueous electrolyte system. The electrical conductivity provides usefulinformation in the area of engineering and in corrosions area providesuseful information for assessing the corrosively of aqueous media andfor the design of cathodic protection system. Also it is used to gaininsight in to the properties of electrolyte solutions and evaluatecharacteristics quantities such as dissociation constants1. Studies onelectrolytic conductance in mixed solvents can provide usefulinformation and sensitive indications of ion-solvent and ion-ioninteractions and solvent structure. The effect of ion association on the

Modern Trends in Science and Technology 2013, pp. 136 - 146Editors: Devendra Adhikari, Shiva Kumar Rai and Kul Prasad LimbuPublishers: Nepal Biological Society, Nepal Physical Society (Eastern Chapter) andResearch Council of Science and Technology


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Modern Trends in Science and Technologyconductance behavior of electrolytes has been a subject of extensiveinvestigation. Although numerous conductance measurements havebeen reported in the literature, such studies in mixed solvents arerelatively rare2. In recent, several studies have reported that the natureof the spherical ions, having a large variation in size in aqueousmixtures of the alcohols, has received considerable attention3.It was reported in the previous work4 that potassium halides arestructure breakers in ethanol-water mixtures and the maximum inbreaking power occurs at 0.1 mole fraction of ethanol. The conductanceof Sodium nitrate in ethanol - water mixtures was measured at 308.15Kin 19795. The measurements of conductance of Sodium Chloride,Potassium Bromide and also Sodium Bromide in pure water andethanol-water mixed solvent media at different temperatures havebeen done6- 8. This paper deals with the conductance behavior ofPotassium nitrate in ethanol-water mixed solvents covering a range ofdielectric constant values at temperatures 303.15, 308.15 and 313.15 K.Experimental methodsEthanol (E. Merck, India) was used for the experimental works. Thepurified ethanol had a density of 0.7820 g/ml and a co-efficient ofviscosity of 0.9821 cp at 303.15 K; these values are in good agreementwith the literature values9. Distilled water with a specific conductanceless than 10-6 S.cm-1 at 303.15 K was used for the preparation of themixed solvents. The physical properties of ethanol-water mixedsolvents were measured at desired temperatures in laboratory.Potassium nitrate (KNO3) employed in these investigations waspurchased from SD Fine Chem Limited, Mumbai, India. Conductancemeasurements were carried out on a Pye-Unicam PW 9509conductivity meter at a frequency of 2000 Hz using a dip-type cell witha cell constant of 1.15 cm-1 and having an uncertainty of 0.01%. The cellwas calibrated by the method of Lind and co-workers in 195910, usingaqueous potassium chloride solution. The measurements were made atthe desired temperatures. The details of the experimental procedurehave been described earlier10, 11. Several independent solutions wereprepared and runs were performed to ensure the reproducibility of theresults. Due correction was made for the specific conductance of thesolvent by subtracting the specific conductance of the relevant solventmedium from those of the electrolyte solutions. In order to avoidmoisture pickup, all solutions were prepared in a dehumidified room


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Modern Trends in Science and Technologywith utmost care. In all cases, the experiments were performed in threereplicates.Results and DiscussionThe alcohol and water associate much less strongly, and formpolymeric H-bonded chains, rather than large cluster, which rarelycontain 5 to 7 molecules for sterically hindered alcohols12. Whenalcohol and water are mixed there is a minute but measurable heat ofsolution that is evident. The hydrogen bonding and closer packing ofthe molecules by the attraction allows a larger number of molecules ofthe hydrated alcohol to fit into the same space, thus decreasing theoverall volume. The density is decreased with the increase of alcoholcontent for the ethanol-water mixed solvent system. This behavior hasbeen found to be similar in the literatures13-15. As a liquid becomeswarmer, the molecules spread out more. When the molecules are morespread out, the substance is less dense, as the specific gravity is lower.Here we investigated the density of water and ethanol and comparisonshas been done between experimental data from this work andliterature data at different temperatures with their references (Table1). Similarly, we also investigated the data and done comparisonsbetween experimental observations from this work and literature datafor viscosity of water and ethanol at different temperatures with theirreferences (Table 2).Tab. 1 Comparisons between experimental data from this work and literaturedata for density of water and ethanol at different temperatures with theirreferences

Literature values9 Experimental valuesT = 303.15 KX2 ρ (g/ml) ρ (g/ml) X2 [Ethanol % (v/v)] ρ (g/ml)0.000 0.9940 0.9940 0.0000 (00%) 0.99570.033 0.9865 0.9824 0.0329 (10%) 0.98410.072 0.9681 0.9693 0.0712 (20%) 0.97130.117 0.9554 0.9545 0.1161 (30%) 0.95560.171 0.9385 0.9377 0.1697 (40%) 0.93870.236 0.9203 0.9189 0.2346 (50%) 0.91920.316 0.8989 0.8980 0.3149 (60%) 0.89970.419 0.8752 0.8749 0.4169 (70%) 0.8776


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Modern Trends in Science and TechnologyT = 308.15 K0.000 0.9924 0.9924 0.0000 (00%) 0.99410.033 0.9785 0.9807 0.0328 (10%) 0.98320.072 0.9665 0.9675 0.0709 (20%) 0.96910.117 0.9546 0.9526 0.1157 (30%) 0.95470.171 0.9359 0.9357 0.1691 (40%) 0.93670.236 0.9168 0.9167 0.2339 (50%) 0.91530.316 0.8930 0.8955 0.3141 (60%) 0.89740.419 0.8707 0.8720 0.4160 (70%) 0.8721T = 313.15 K0.000 0.9905 0.9905 0.0000 (00%) 0.99220.033 0.9763 0.9788 0.0327 (10%) 0.98090.072 0.9633 0.9655 0.0707 (20%) 0.96690.117 0.9503 0.9505 0.1153 (30%) 0.95080.171 0.9328 0.9336 0.1686 (40%) 0.93210.236 0.9139 0.9145 0.2332 (50%) 0.91340.316 0.8896 0.8931 0.3133 (60%) 0.89150.419 0.8671 0.8694 0.4151 (70%) 0.8617Tab.2 Comparisons between experimental data from this work and literaturedata for viscosity of water and ethanol at different temperatures with theirreferences

Literature Values9 Experimental ValuesT = 303.15 KX2 η (cp) η (cp) X2 [Ethanol % (v/v)] η (cp)0.000 0.7982 0.7982 0.0000 (00%) 0.79750.033 1.0200 1.0229 0.0329 (10%) 1.12620.072 1.4539 1.2817 0.0712 (20%) 1.40310.117 1.7660 1.5525 0.1161 (30%) 1.67310.171 2.0492 1.7925 0.1697 (40%) 1.88160.236 2.2487 1.9422 0.2346 (50%) 1.99120.316 2.0666 1.9483 0.3149 (60%) 1.95570.419 1.8958 1.8074 0.4169 (70%) 1.8160T = 308.15 K0.000 0.7202 0.7202 0.0000 (00%) 0.71940.033 0.9015 0.9198 0.0328 (10%) 0.92060.072 1.2355 1.1491 0.0709 (20%) 1.1610


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0.117 1.4731 1.3886 0.1157 (30%) 1.39040.171 1.7568 1.6011 0.1691 (40%) 1.51100.236 1.7896 1.7346 0.2339 (50%) 1.60790.316 1.6249 1.7425 0.3141 (60%) 1.57630.419 1.5197 1.6214 0.4160 (70%) 1.5015T = 313.15 K0.000 0.6531 0.6531 0.0000 (00%) 0.65310.033 0.7975 0.8305 0.0327 (10%) 0.83210.072 1.0857 1.0335 0.0707 (20%) 1.00830.117 1.3168 1.2446 0.1153 (30%) 1.17130.171 1.5674 1.4310 0.1686 (40%) 1.33110.236 1.5924 1.5472 0.2332 (50%) 1.38530.316 1.4442 1.5528 0.3133 (60%) 1.37040.419 1.3584 1.4450 0.4151 (70%) 1.2954It was observed that the density decreases with increase inethanol percentage and viscosity increases reaching maximum at 50percent ethanol and decreases for range investigated (Figures 1 and 2).In spite, of this trend, the specific conductivity decreases with increasein ethanol percentage, thus suggesting other factors other thanviscosity and density of medium contribute toward the conductancebehavior of the ions. This behavior has been found to be similar in theliteratures16. We also observed that dielectric constant decreases withincrease in the volume fractions of ethanol at different temperatures(Figure 3).

Fig. 1 Density as a function of the volume fractions of Ethanol at differenttemperatures.0.86

0.90

0.94

0.98

1.02

0 0.2 0.4 0.6 0.8

303.15 K308.15 K313.15 K

Volume Fraction

(g

/ml)


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Fig.2 Viscosity as a function of the volume fractions of Ethanol at differenttemperatures.

Fig. 3 Dielectric constant as a function of the volume fractions of Ethanol atdifferent temperatures.The experimental specific conductivities of Potassium nitrate as afunction of the salt concentration (cs) at 303.15, 308.15 and 313.15 K ofseven different ethanol-water mixtures (containing 0.10, 0.20, 0.30,0.40, 0.50, 0.6 and 0.70 volume fractions of ethanol) are depicted inFigures 4, 5 and 6 respectively. The figures show the specificconductivities exhibit a sharp increase with increasing concentration

0.6

1.0

1.4

1.8

2.2

0 0.2 0.4 0.6 0.8

303.15 K308.15 K313.15 K

Volume Fraction

(c

p)

30

40

50

60

70

80

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

303.15 K308.15 K313.15 K

volume fraction

Die

lect

ricC

onst

ant()


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Modern Trends in Science and Technologywithin the concentration range investigated. The increase in thespecific conductance with increase in concentration is due to theincrease in the number of ions per unit volume of the solution.

Fig. 4 Specific conductivities of KNO3 as a function of the salt concentration (cs)at 303.15 K (Solid lines – fitted graphs).

Fig. 5 Specific conductivities of KNO3 as a function of the salt concentration (cs)at 308.15 K (Solid lines – fitted graphs).Obviously, the concentration dependence of the specific conductivityfollows the same pattern at all solvent composition investigated. In fact,

0

0.005

0.010

0.015

0 0.04 0.08 0.12

10% Ethanol20% Ethanol30% Ethanol40% Ethanol50% Ethanol60% Ethanol70% Ethanol

Cs (Mol L-1)

(S

cm-1

)

0

0.005

0.010

0.015

0 0.04 0.08 0.12


Cs (Mol L-1)

(S

cm-1

)


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Modern Trends in Science and Technologythe variations of specific conductivity with electrolyte concentrationsare always found to be linear. We, therefore, determined the slopes(Table 3). The possible explanation for the positive slopes in thepresent mixed solvent media may be that the counter ion bindingwould become quite appreciable in these media as the concentration ofthe electrolyte is increased, thereby weaker ion-solvent interactions. Asa consequence, contraction of the solvent would be gradually loweredwith increasing concentration of the electrolyte, resulting in a netpositive volume change per mol of the added electrolyte. The values ofslopes also increase with increase in temperature, it indicates thatconductivity increases (Table 3) with increase in temperature due toincrease in ionic mobility. Moreover, the slopes are found to decrease inthe mixed solvent media become richer in ethanol.

Fig. 6 Specific conductivities of KNO3 as a function of the salt concentration (cs)at 313.15 K (Solid lines – fitted graphs).The relative permittivity of the medium decreased at a giventemperatures with increasing in the ethanol content and this trend hasalso been seen in the conductivity study17-21 of methanol content inwater. The conductance decreases with increase of alcohol content forthe studied ethanol-water mixed solvent system. Which indicate anincrease in ionic association and re-in forces the concept of theformation of solvent-separated ion pair with decrease in dielectricconstant, thus electrolyte behavior depends on dielectric constant22.

0

0.005

0.010

0.015

0 0.04 0.08 0.12


Cs (Mol L-1)

(S

cm-1

)


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Tab.3 Experimental slopes and the correlation coefficients of fits (as r2) ofpotassium nitrate in Ethanol-Water mixtures at different temperatures.

ConclusionsWe conclude from this study that conductivity of potassium nitrate inethanol-water binary solvent depends in concentration and relativepermittivity of the medium rather in density and viscosity of themedium. The relative permittivity of the mixed solvents decreases withincrease in ethanol content. Also the specific conductivities are found toincrease with increasing concentration of the electrolyte solution overthe entire concentration range investigated whereas the specific

T/K Slope r2 Dielectric constant0.10 volume fraction of ethanol303.15 0.111 0.998 72.00308.15 0.117 0.999 71.00313.15 0.119 0.999 69.100.20 volume fraction of ethanol303.15 0.0917 0.999 67.32308.15 0.0951 0.999 66.37313.15 0.0961 0.999 64.050.30 volume fraction of ethanol303.15 0.0745 0.999 62.07308.15 0.0773 0.998 61.33313.15 0.0804 0.996 58.740.40 volume fraction of ethanol303.15 0.0636 0.998 56.89308.15 0.0671 0.999 56.29313.15 0.0691 0.997 53.840.50 volume fraction of ethanol303.15 0.0541 0.998 51.48308.15 0.0572 0.997 50.70313.15 0.0604 0.995 48.930.60 volume fraction of ethanol303.15 0.0485 0.999 45.77308.15 0.0504 0.998 44.98313.15 0.0507 0.997 43.890.70 volume fraction of ethanol303.15 0.0407 0.997 40.08308.15 0.0415 0.997 39.26313.15 0.0448 0.997 37.62


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Modern Trends in Science and Technologyconductivities of potassium nitrate decrease with decreasing dielectricconstant of solvent composition.AcknowledgementsThe authors are grateful to Nepal Academy for Science and Technology(NAST), Kathmandu for financial support, Professor Dr. Sujeet KumarChatterjee, the department of Chemistry, Mahendra Morang AdarshMultiple Campus, Tribhuvan University, Biratnagar, Nepal for thevaluable suggestions and discussions. The authors are also thankful toAssociate Professor Sant Kumar Bhagat, Campus Chief and BasudevKafle, Head of the department of Chemistry, Damak Multiple Campus,Tribhuvan University, Damak, Nepal for providing us the researchfacilities to conduct this research work.References

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