Investigation of relative hydrophobicity of
aqueous solutions of some sodium salts

E.A. Masimov, A.A. Hasanov , Кh. T. Akhmedova
Baku State University, Physics Department, Research Laboratory "Physics and chemistry of solutions
of macromolecule", Z. Khalilov str. 23, Baku 370145, Azerbaijan Republic

ABSTRACT

                               The relative hydrophobicity of aqueous solutions characterizes the ability of                       dissolved substance to modify water. The quantitative estimation of this parameter was                       carried out by distribution of substances-markers (homologous series of DNP-amino                       acids with aliphatic side-chains) in water-organic two-phase system water-octanol.
                               In the present paper, the relative hydrophobicity of aqueous solutions of some                       sodium salts was determined. It was revealed, that all salts hydrophobicy water at their                       concentrations up to certain critical value, and further increasing of concentration does                       not change the hydrophobic properties of aqueous solution. Depending on the ability to                       act on water we can align these salts in following sequence:

                NaJ > NaCNS > NaC2H3O2 > NaBr > Na2SO4 > Na2CO3 > NaCl > NaPO3 > NaF > Na3PO4

                               Such a sequence of the same salts takes place depending on the values of their                         limiting dissolubility in water. The found correlation between the limiting dissolubility                         and the limiting value of relative hydrophobicity can be explained by the correlation,                         found by us earlier, between the relative hydrophobicity of solutions and the relative                         hydrophobicity of chemical compounds (their affinity to aqueous medium)

Key words: two-phase water-organic systems, the hydrophobicity of aqueous solutions, the maximum dissolubility in water, sodium salts.

            Numerous investigations have shown that the presence of different high-molecular      and low-molecular additions in the water changes the thermodynamic state of water that      in turn is reflected on the degree of hydrophobic effect in an aqueous medium. In particular, it has been shown [1] that the water properties in the presence of electrolytes         differ from those of the pure water. The different ions have a different effect on the water structure in this case.
            The affinity to aqueous solution of a nonpolar methylene group in comparison with the affinity to pure water of the same group has been proposed as the characteristic of a relative hydrophobicity of aqueous solution [2,3].
              To estimate the value of free energy of CH2-group transition from the water medium to the organic solvent (octanol), the dependence of the logarithm of distribution coefficient (ln P) of a series of sodium salts of dinitrophenyled aminoacids with the hydrophobic tails differing in length of hydrocarbon radical on the effective number (n)

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