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sodium solutions properties

sodium solutions properties - Journal o f Solution...

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Journal of Solution Chemistry, l/ol. 11, No. 3, 1982 Enthalpies and Heat Capacities of Transfer of Sodium Carboxylates and Sodium Dodecylsulfate from Water to Aqueous fert-Butyl Alcohol Solutions N. Roy Choudhury I and I. C. Ahluwalia 1'2 Received January 27, 1981; revised April 12, 1982 Integral enthalpies of solution at very low concentrations of sodium carboxylates and sodium dodecylsutfate in aqueous tert-butyl alcohol solutions at 25~ and 35~ were measured with an isoperibo/ submarine calorimeter. The enthalpies and heat capacities of transfer of these surfactants from water to aqueous tert- butyl alcohol solutions were derived from integral enthalpies of solution. The results are explained in terms of the structural alteration effect of the constituent hydrophobic and hydrophilic groups of the solute. KEY WORDS: Enthalpies of transfer; heat capacities of transfer; sodium carboxylates; sodium dodecylsulfate; left-butyl alcohol-water mixed solvent; hydrophobic and hydrophilic effects. 1. INTRODUCTION Alcohol-water mixed solvent media, and in particular aqueous tert-butyl alcohol (t-BuOH), are widely studied hydrophobic systems. (14~ In the study of the t-BuOH-water system, many properties of the solute show extrema at around 0.04 mole-fraction (mf) /-BuOH. (3'4~ However, despite numerous studies a clear understanding of the nature of the various interactions responsible for such extrema is still lacking. Fur- thermore, the dependences of the position and magnitude of the extrema on the nature and size of the solute are not yet fully under- stood. In the study of ternary systems, the thermodynamic transfer 1Department of Chemistry, Indian Institute of Technology, New Delhi-110 016, India. 2To whom correspondence should be addressed. 189 0095-9782/82/0300-0189503.00/0 1982 PLenum Publishing Corporation
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190 Choudhury and Ahluwalia functions of the solute are useful in elucidating the nature of inter- actions taking place in the system. Of particular importance are the enthalpies and heat capacities of transfer as these functions are sensi- tive to structural effects of the solvent. It is important to know how the transfer functions vary with the size of the hydrophobic group present in the solute. For this purpose we chose the sodium carboxylate series as suitable solutes, varying the chain length of the alkyl group from one to twelve. We report in this paper the enthalpies and heat capacities of transfer of sodium formate (NaC1), sodium acetate (NaC2) , sodium propionate (NaC3), sodium butyrate (NaC4) , and sodium dodecanoate (NaC12) from water to var- ious concentrations of t-BuOH-water mixed solvent. In order to under- stand the effect of the polar (hydrophilic) functional group on these transfer functions, we have also reported the enthalpies and heat capac- ities of transfer of sodium dodecylsulfate (NaDS) from water to t- BuOH-water mixed solvent.
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