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Latin American applied research

On-line version ISSN 1851-8796

Lat. Am. appl. res. vol.44 no.2 Bahía Blanca Apr. 2014

 

Densities and excess molar volumes for binary solution of water + ethanol, + methanol and + propanol from (283.15 TO 313.15) K

A. Shalmashi and F. Amani

Chemical Technology Department, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran. E-mail: Shalmashi@irost.org, Fa.amani@yahoo.com

Abstract- Densities for binary solutions of three alcohol (Ethanol, Methanol and propanol) with water over the whole composition range have been measured at temperatures from (283.15 to 313.15) K in 10 K intervals and atmospheric pressure (101.3 kPa). From these data, the excess molar volumes (VE) were calculated. The excess molar volumes for these systems were found to be negative across the whole composition and at all temperatures investigated. The excess molar volumes for ethanol and propanol + water become less negative with increasing temperature and conversely the excess molar volumes for methanol+ water become more negative with increasing temperature. The standard deviations (σ) for densities were calculated that ranged from 0.0000 to 0.001.

Keywords- Density; Excess Molar Volume; Binary Solution; Dielectric Constant.

I. INTRODUCTION

In ideal solutions there are interactions between molecules, but the average A-B interaction in the mixture are the same as the average A-A and B-B interactions in the pure liquids. Real or non-ideal solutions are composed of particles for which A-A, A-B and B-B interactions are all different. The thermodynamic properties of real solutions may be expressed in terms of the excess functions, XE, defined as the difference between the observed thermodynamic function of mixing and the function for an ideal solution.

The excess volumes are defined as:

VE = V (real solution) - V (ideal solution)

VE = Volume of the solution - (volume of pure A +volume of pure B).

Among the various thermodynamic properties, the excess molar volume, VE, has been of much interest for the practical purpose of determining composition from the density measurement (Rathnam et al., 2008; Redlich and Kister, 1948). Density and excess molar volume are significant for the design of new processes and the study of molecular interactions in binary liquid systems (Chen and Knapp, 1995; Wahab et al., 2002). Excess volume could provide information on the possible interactions between components of a binary mixture, such as molecular associations and dipole-dipole and dipole-induced-dipole intractions (Rathnam et al., 2008; Jimenez et al., 2004). Furthermore excess volumes could indicate the deviation of a binary solution from the ideality.

In this paper we have reported the density and excess volumes, VE, for binary systems including water with ethanol, methanol and propanol, over whole mole fraction range at (283.15 to 313.15) K in 10 K intervals and atmospheric pressure. This study is expected to give some information about the volume changes in these binary solutions that indicate the tendency of the water molecules with simple alcohols.

II. METHODS

A. Materials

The chemical, absolute alcohol, methanol and propanol were high-purity grade reagents obtained from Merck (Darmstadt, Germany). Bidistilled water was used to prepare the sample mixtures.

B. Apparatus and procedure

The densities of the pure components and binary mixtures were measured using an approximate 25 cm3 Gay-Lussac pycnometer supplied by a thermometer, which was calibrated by using pure water. The temperature of the solution in the pycnometer was kept constant in a bath with a thermostat. The temperature was controlled within ±0.05 K of the desired temperature through thermometer of the pycnometer. Once the solution reached the desired temperature, they were weighted to within ±0.0001 g with an analytical balance (Sartorius, 2842, GMBH, Germany). The solution of each composition were prepared fresh and just before use by mass. For each binary mixture, a set of 9 composition from (10 to 90) % w/w, was prepared and their densities were measured at the respective composition. Each reported value was the average of at least three measurements. The densities of the pure materials together with literature values are presented in Table 1. With regards to calculated standard deviations (σ) the uncertainty in the density for pure liquids and prepared binary mixtures was found to be from 0.0000 to 0.001. All experiment was done at atmospheric pressure (i.e. 101.3 kPa).

Table 1. Densities of pure compound at different temperatures with literature data

a. Perry and Green (2008). I ethanol, II. methanol, III. propanol, IV. Water

III. RESULTS AND DISCUSSIONS

Experimental values of density are used to calculate VE of the mixtures as:

(1)

where M1 and M2 are the molecular weights of components 1 and 2; ρ1 and ρ2 are the densities, and x1 and x2 are the mole fractions of the respective components. The symbol ρ stands for the mixture density (Li et al., 2008).

The experimental data on the densities and excess volumes for binary solutions of ethanol, methanol and propanol with water at temperature from (283.15 to 313.15) K over the whole composition range are presented in Tables 2 to 4, respectively and graphically represented in Figs. 1 to 3.

Table 2. Experimental Densities (ρ) and Excess molar volumes (VE) for the ethanol with water binary solutions at different temperature and composition. * Ethanol mol fraction

Table 3. Experimental Densities (ρ) and Excess molar volumes (VE) for the methanol with water binary solutions at different temperature and composition. * Methanol mol fraction

Table 4. Experimental Densities (ρ) and Excess molar volumes (VE) for the propanol with water binary solutions at different temperature and composition. * Propanol mol fraction


Figure 1. Excess molar volume as a mole fraction for the Ethanol + water mixture at different temperatures: 283.15 K; × 293.15 K; ◊ 303.15 K; Δ 313.15 K.


Figure 2. Excess molar volume as a mole fraction for the Methanol + water mixture at different temperatures: 283.15 K; × 293.15 K; ◊ 303.15 K; Δ 313.15 K.


Figure 3. Excess molar volume as a mole fraction for the Propanol + water mixture at different temperatures: 283.15 K; × 293.15 K; ◊ 303.15 K; Δ 313.15 K.

The results presented in Tables 2 to 4 and Figs. 1 to 3 indicate that VE values are negative for binary solutions of ethanol, methanol and propanol with water over the entire mole fraction range and at all temperatures investigated for each binary system under study. The VE profiles of all binary systems studied are characterized by an initial increase in negative values following maxima at about 60-70 % (w/w) and then a decrease. In each four temperature investigated, less negative excess volume is related to the binary mixture of propanol + water.

Dielectric constant (e) is a function of temperature. The value of this factor for methanol, ethanol and propanol at 293.15 K respectively are 33.0, 25.3, and 20.8 (Lide, 2010). The maximum excess molar volumes at mole fraction 50% for each of the three alcohols in water at temperature 293.15 K were showed in Fig. 4. As is clear in this diagram, the most negative excess molar volume in mole fraction 50% at 293.15 K is belong to ethanol.


Figure 4. The effect of polarity of alcohols on maximum excess molar volumes at mole fraction 50% of alcohol in water at temperature 293.15 K.

IV. CONCLUSION

As data in this study show, the excess volumes for all three studied alcohol with water in each four investigated temperature were found to be highly negative across the mole composition. It is obvious that hydrogen bonds between the molecules of water and alcohol are primary responsible for the non-ideal behavior of these binary systems (Grguric et al., 2002; Jimenez et al., 2004).

As figures show, the excess molar volumes for ethanol and propanol + water become less negative with increasing temperature and conversely the excess molar volumes for methanol+ water become more negative with increasing temperature (Zarei et al., 2007; Jimenez et a.l, 2004 ).

For the methanol + water system, the temperature effect is hardly observable (Bai et al., 1999).

Also the results showed the most negative excess molar volume in mole fraction 50% at 293.15 K was belonging to ethanol.

REFERENCES
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Received: October 18, 2012
Accepted: Jannuary 28, 2013
Recommended by Subject Editor: Mariano Matín

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