The subject of this thesis deals with three main topics which may be summarized in following: 1. Investigation of some physical properties ; (densities dielectric constants, specific conductance's , and refractive indices) of different compositions of both glycerol- water (GL-W) and ethylene glycol-water (EG-W) mixtures at different temperatures in the range 283.15-313.15 K, 2. Studies of the thermodynamics of HC1 transfer from water to GL-W and to EG-W mixtures. Three different compositions of GL-W have been tested containing 35.97 (X2=0. 09.9027), 60. 30 (X2=0.296486) and 83.22 (X2-0 .492433 ) weight percentages of glycerol and two compositions of EG-W containing 27.67 (X2= 0.099914) and. 59.64 (X2 =0.300178) weight percentages of ethylene glycol have also been examined. 3. Determination of the first and second dissociation constants and the related thermodynamic quantities of both amino acids glycine and DL-alanine in both solvent mixtures; The study also covered the thermodynamic quantities of transfer of the amino acids from water to GL-W or to EG-W mixtures. Electromotive force measurements with hydrogen - silver / silver chloride electrodes in cells without liquid junction have been used to evaluate the standard potentials of the Ag, AgCl electrode in EG-W and in EG-W mixtures at four different temperatures in the range 283.15- 313.15 K. The standard thermodynamic functions for the cell reaction and the standard thermodynamic quantities for the transfer of HC1 from water to either GL-W or to EGW mixtures have also been determined . The results showed that the transfer free energies Δt G° of HC1 from water to the mixtures became less negative as the mole fraction X2 of GL or EG in the mixtures decreased . The data also showed that Δt S° values either increased slightly , or remained almost constant, over the initial increase in X2 values followed subsequently by some decrease. The decreasing behaviour began at earlier composition in EG-W than in GL-W mixtures, ΔtH° underwent a slow decrease with the initial increase of X2 , decreasing thereafter substantially with increasing values of X2 . The negative and decreasing values of ΔS° and ΔH° implied a gradual breakdown of water structure, as a consequence of the transfer process, with further addition of glycerol or ethylene glycol to the highly polar water molecules. Δt Cp° values were positive for all solvent compositions and increased with increasing glycerol content, while for EG-W system, ΔtCp° values increased to maximum, decreasing, thereafter, as X2 increased to≈ 0.3. The electrostatic effect
arising from the difference in dielectric constants have been found to be fairly small compared with the respective total changes in Δt G° . The chemical part of the free energy of transfer Δt Gch° , was shown to be positive. Both the electrostatic and i chemical parts of the enthalpy and entropy of -transfer were generally negative. The dissociation constants pK2 and pK2 for glycine and DL-alanine in both solvent mixtures were determined from e.m.f. measurements of cells without liquid junction at four different temperatures in the range 283.15-313.15 K. The values of the pK1 and pK2 of glycine and DL-alanine were utilized for the determination of the thermodynamic quantities (ΔtG° , ΔtH°, ΔtS° and ΔtCp°) for the two dissociation processes. The data were also used to determine the thermodynamic quantities for the transfer of the acid from the solvent mixture to water and of the dissociation products from water to the solvent mixture. The variation of pK1 values for both acids in both solvent mixtures (GL-W or EG-W) was shown to be less temperature dependent than the corresponding values of pK2 . This was ascribed to a higher heat of the acid dissociation in the second stage of dissociation as compared with the first stage. The results of pK1 and pK2 for both acids in both solvent mixtures indicated that: (i ) pK1 values for both acids at 93.15K.remained the same up to values X2=0.1 .beyond which the values of pK2 at any value of X2 remained in GL-W mixtures slightly higher for DL-alanine than of glycine; (ii) pK2 values in GLW mixtures at 293.15K. remained considerably higher for DL-alanine than of glycine. (iii) Values of pK1 in EG-W at 293.15 for various values of X2 remained very much similar for both acids, while pK2 values were slightly greater for DL-alanine than of glycine . The results indicated that the extent of the acid dissociation in EG-W mixtures at constant temperature was somewhat greater, for both stages of the dissociation, for glycine than for DL-alanine. On the other hand, the dissociation of both acids occurred to the same extent in the first as well as in the second dissociation stages when the solvent mixture was GL-W. The variation of ΔtG° values for both acids in the both solvent mixtures with the variation of Xz occurred to more positive values. The increase of AG values was slightly smaller for the second dissociation stage as compared with the first dissociation stage. The ΔtH° values for glycine dissociation in GL-W mixtures increased with increasing X2 up to X2 = 0.3 decreasing thereafter as X2 increased. Thus, further addition of glycerol beyond X2 - 0.3 was accompanied with a decrease in enthalpy. Variation of ΔH° values of glycine in EG-W was toward more endothermic values with increasing values of X 2. The behaviour of DL-alanine in GL-W mixtures were very similar to those of glycine except that the initial increase of ΔtH° continued to a maximum in the case of DL-alanine. Values of ΔS° for the first dissociation stage of both acids were more negative in GL-W as well as in EG-W than in water. A similar behaviour was also observed for the second dissociation stage for most values of X2. The results of the thermodynamic quantities of transfer of both glycine and DL-alanine from water to both aqueous .'glyoerol or to ethylene glycol mixtures indicated that Δt G° values for the both dissociation processes of . the acids were positive and increased as the values of X 2 increased. The positive values of Δt G° implied a net effect in which stabilization of RH2 acid or of destabilization of protons and/or R predominated when GL or EG was added to the aqueous solvent. ΔtH° values for glycine in GL-W mixture increased with increasing values of X2 to 0.3 beyond which there was a subsequent decrease in ΔtH° with further increase of X2 for both dissociation transfer stages, while in EG-W mixture, ΔtH° values did not alter significantly with the variation of X2 values. The behaviour for the first dissociation transfer stage of DL-alanine in both solvent mixtures was very much similar to that of glycine. In the second dissociation transfer stage of DL—alanine in GL-W mixture there was a slight increase in ΔtH° values with X2 . Δt S° values decreased generally with increasing values of X2 although this was either initiated or followed by a slight increase in certain cases. The decreasing tendencies of A S values with increasing values of X2 suggested a pronounced ordering of the system when zwitter ion, II and NH2RC02 particles were present in the solvent mixtures. Δt Cp values of glycine increased initially in GL-W mixture, this was followed by a sharp decrease which was, thereafter followed by a substantial increase as X2 increased. With DL-alanine in the same solvent mixtures , Δt Cp first decreased as X2 increased .which either continued decreasing or increased with further rise in the value of X2 . In EG-W mixture, the first dissociation transfer stage was generally similar to that in GL-W with respect to both acids provided the initial increase in Δt CP° values which was observed in GL-W was ignored. This may also be applied to the second dissociation stage of DL-alanine . With glycine in EG-W mixture, the behaviour of this acid became very much similar to that of DL-alanine.