The Subject of the present thesis involved three main lines which may be summarized as follows: .1- The study of the physical properties of two mixed solvents invol vi ng: a- urea-water, b- sodium carboxymethyl cellulose water (CMCwater). The study covered the measurements of the densities (d). viscosities (γ) dielectric constants (D) and specific conductances (σ) of the two types of the solvent mixtures at six temperatures which were: 293. 1 5, 298.15, 303.15, 308. 15, 313. I5 and 318.15 K and at four compositions of each of the urea-water and CMC-water mixtures. The deviation of the solvent mixtures from an ideal volume mixture relation was examined from the dielectric properties of the mixtures and of their individual constituents. The volume tric behaviours of urea-wat.er and CMCwater mixtures have been investigated in terms of excess molar volume. The variation of the dielectric constant deviation function (ΔD) with the volume fraction of the organic component of the mixture was interpreted in terms of the change in the degree of alignment of the dipoles with changing the composition as a consequence of the destruction, caused by urea or CMC, of the three-dimentional hydrogen- bonded water structure. The variation in the
relative excess molar volumes of the mixtures was found to be due to a volume contraction ( negative ΔD) on mixing the constituents of the. mixture. The results were rationalized in terms of the two models for liquid water; one maximally hydrogen-bonded and voluminous, the other non-hydrogen -bonded and dense. The effect of the added organic co-solvent to water was to shift this equilibrium in one direction or the other. The activation energy (E) for ion flow in urea-water or CMC-water mixtures could be estimated from the dependence of viscosity on temperature; the larger viscosities of the CMC-water solutions than of urea-water may account for the difference between the two sets of E values. 2- The study of physical properties of the solutions of tetraethyl ammoniurn bromide (TEAB) in different solvents which were: 1 - water; 2- urea-water mixtures; and, 3- CMC—water mixtures. The study also covered the measurement of densities (d), viscosities (γ) and molar conductances (Δ) TEAD solutions at ten different concentrations of this substance in the range 0. 0097-0. 1203 mol dm-³ . The investigations covered the four compositions of each of the ureawater and of CMC-water mixtures at six different temperatures in the range 293.15- 318. I5 K. Electrolytic solutions of moderate concentration generally have relative dynamic viscosities (γ) which obey the empirical equation of Jone and Dole, the dependence of values on the concentration © of the TEAB in water or in urea-water or in CMC-water mixtures have been determined. The effective radius ® of the cation result ing f rom the dissociation of TEAB molecules in the solvents has been calculated and found to decrease with decreasing values of γ or o f D. The effect of D in reduc ing the va lue o f r+ i s likely to be subst a ntialan dgreater than of γ . Th i s i s more obvious in comparing the r + data obtained in water and in urea-water with those estimated in CMC-water systems. 3- The possibility of ion association In the solvents containing TEAB electrolyte was examined at a number of solvent compositions and temperatures. The results for ion-pair formation have been expressed in terms of the association constant (KA) of the TEAB. Values of KA have first been determined from Bjerrum picture of ion-pair formation. Val ues of KA»-have also been determined from the experimentally measured conductances using a 1east—square treatment with an appropriate computer programme using shedlovsky method. The agr e ement of the KA values obtained by the two di f ferent methods was substantially high. 4- The mean activity coefficients of TEAB at various concentrations in the mixed solvents and at the different experimental temperatures could be estimated from the extended Debye-Huckel equation. The limiting molar conductances of the electrolyte in the various solvent mixtures and temperatures have also been determined. The walden products for TEAB in the solvent mixtures could be obtained from the product of the limiting ionic conductance and the viscosity of the solvent mi xture. 5-The possibility of the formation of triple ions in the TEAB solutions in the mi xed solvents has also been examined using a modified Fuoss-Kraus theory taking into account the activity coefficient of the electrolyte. The results have been expressed in terms of the dissociation constants of the triple ions in the various solvent mixtures and temperatures. 6- An attempt was also made to determine the thermodynami c quantities for ion-pair formation at the different experimental conditions.