Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates in Aqueous Solution |
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Authors: | Tejas Joshi Jitendra Mata Tejas Patel |
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Institution: | 1. Department of Chemistry , Veer Narmad South Gujarat University , Surat, India tejasjoshi_surat@yahoo.co.in;3. Department of Chemistry , Veer Narmad South Gujarat University , Surat, India |
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Abstract: | The aggregation behavior of metal dodecyl sulfates (MDS), Na1+, Mg2+, Mn2+, Co2+, and Ni2+] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion dissociation (β) evaluated from conductivity data. Using law of mass action model, the thermodynamic parameters viz. Gibbs energy (ΔGm 0), enthalpy (ΔHm 0), and entropy (ΔSm 0) were evaluated. The enthalpy of micellization decreases strongly with increasing temperature. ΔG is always negative (thermodynamically favored process) and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of the counterion. The plots of differential conductivity, (dk/dc) T,P , versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. Surfactants with strong condense counterion are adapted to rodlike micelle better than to a spherical micelle. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counterion. |
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Keywords: | Micellization counterion thermodynamic parameters differential conductivity |
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