Precious fit excess molar volumes [172]. Fardad Koohyar et.al.

Precious N. Sibiya and NirmalaDeenadayalu have worked on methanol or ethanol or 1-propanol + ionic liquid.Determined excess molar volume and partial molar volume at temperatures 298.15,303.15 and 313.15 K. values fitted with Redlich-Kister polynomial equation 171.Diana M.

Cristancho et.al. Studiedpartial molar volumes and excess molar volumes of water + glycerol mixtures at288.15 to 303.15 K.

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Redlich-Kister equation used to fit excess molar volumes172.Fardad Koohyar et.al.

Reportedexcess molar volumes, change of refractive indices on mixing and viscocity foraqueous solutions of ethanol, methanol, 1-propanol, ethylene glycol and1,2,3-propane triol at 292.15 K. measurement done over whole mole fractionsrange at atmospheric pressure. Redlich-Kister polynomial equation used forcorrelating excess thermodynamic properties and derives the coefficients andstandard errors 173.Alain Valtz et.al.

reporteddensities and excess molar volumes for water + Diethylene glycolamine andmethanol, ethanol, water, 1-propanol + triethylene glycol at 283.15 and 363.15K in 10 K intervals at the atmospheric pressure. Redlich-Kister equation usedto correlate experimental results 174.3.

3Result and DiscussionIn this study,densities, ? of methanol, ethanol and n-propanol with water were measured overthe entire composition range at temperatures from 293.15 to 313.15 K.The experimentaldensities of pure water, methanol, ethanol and n-propanol are shown in table 3.1along with literature values and in table 3.2 experimental and literaturedensities ? and excess molar volume values of binary liquids at varioustemperatures for various mole fractions of alcohols are given.

The closenessbetween experimental results and literature results has been satisfactory.The excess molar volume anddensities of water with methanol, ethanol and n-propanol at (293.15 to 313.15)K are reported in tables 3.3, 3.4 and 3.5 and shown graphically in figures 3.1,3.

2, 3.3, 3.4, 3.5 and 3.6.

Densities and corresponding VEdata at various temperatures were given in table 3.3, 3.4 and 3.5. Plots ofdensities with respect to mole fraction of methanol, ethanol and n-propanol inwater were shown in figures 3.1, 3.

3 and 3.5. From this there is continuousdecrease in densities with the same rate on addition of alcohols like methanol,ethanol and n-propanol in water with slight variation.Excess molar volume VEfor methanol, ethanol and n-propanol in water have been plotted in figures 3.2,3.

4 and 3.6. From this figure VE found to be negative with largemagnitude. All the binary mixture shows well defined minima 159. Fromnegative values of excess molar volume there is some specific type of interactionbetween mixing component. It indicates that there is intermolecular H-bonding.

The negative value of VE indicates there is interstitialaccommodation of alcohol in the H-bonded aggregates of water 167.The negative VE values dueto there are chances of specific interaction, interstitial accommodation andchange in free volume. There are some specific interactions occurring betweenalcohols and water and it depends on amount of water or alcohols present in themixture. More negative value of VE shows that there is increase ininteractions.

Because of this reason there is decrease in volume. In alcohol Hof –OH group is polar similar to water so there is chances of formation ofH-bonding in alcohols 169.Another reason for volume reductionis the hydrophobic interactions of alcohols in which there are chances ofoccupation of hydrophobic molecule in the spaces or cages of water molecule157.Initially there is small proportionof alcohols and large proportion of water so interaction is less betweenmolecules as proportion of alcohol increases upto mole fraction of alcohol is0.5, then the excess molar volume VE decreased and become negative.

Thenafter as the proportion alcohols increases there is dissociation of componentsor chances of formation of weaker bond between component causes expansion ofvolume so the excess molar volume VE increases.From figures 3.2, 3.4 and 3.6 it isseen that as the number of carbon atoms in alcohols increase the negativevalues of excess molar volume VE goes to decreases.             According to R.F. Lama and B.

C. – Y.Lu, ethanol – water mixtures exhibit more negative excess entropy of mixingthan do methanol – water mixtures 175.Additionally,more recent ab initio calculations on methanol – and ethanol – water clustersindicate that the ethanol – water hydrogen bonding interaction is slightlystronger than the methanol – water interaction 176.RoyceK.

Lam et al investigated mixtures of methanol, ethanol with water by liquidmicrojet X-ray absorption spectroscopy on the oxygen K – edge, the measureddata evidence a significant enhancement of hydrogen bonding originating fromthe methanol and ethanol hydroxyl groups upon the addition of water, theseadditional hydrogen bonding interactions would strengthen the liquid – liquidinteractions resulting in additional ordering in the liquid structures andleading to a reduction in entropy and a negative enthalpy of mixing, consistentwith existing thermodynamic data 177.Abovestudy is agree with experimental data in which water –ethanol shows morenegative VE as compare to water – methanol mixtures.