Partial molar volumes of citric acid and tartaric acid have been determined in water and binary aqueous mixtures of ethanol (5, 10, 15, 20 and 25% by weight of ethanol) at different temperatures and acid concentrations from the solution density measurements. The data have been evaluated by using Masson equation and the obtained parameters have been interpreted in terms of solute-solvent interactions. The partial molar volumes vary with temperature as a power series of temperature. Structure making/breaking capacities of the organic acids have been inferred from the sign of [∂ 2 φv 0 /∂T 2 ] p , i.e. second derivative of partial molar volume with respect to temperature at constant pressure. Both the organic acids behave as structure breakers in water and water + ethanol.
Experimental results for the measurement of hydrodynamic permeability, electro-osmotic velocity, electro-osmostic pressure and streaming potential for different aqueous solutions of urea and thiourea across the cation-exchange membrane (Indion 236, Sd fine chemicals, India) at 30 °C and voltages up to 25 V are reported. The results have been analysed in the light of thermodynamics of irreversible processes. The cation-exchange membrane has been characterised in terms of effective cross-sectional area, equivalent pore radius, and frictional coefficient. The permeability coefficient L P , has been found to be independent of the hydraulic pressure but is a characteristic property of the membrane and depends upon the concentration of the solute. The reflection coefficient σ, has also been evaluated. Onsager's reciprocity relation has not been found to hold well and this may be attributed to the higher polarization in case of electro-osmosis and also to the highly charged character of the membrane. The efficiencies of maximum electro-kinetic energy conversion took place at half the value of the electroosmotic pressure in each case but the value of maximum energy conversion has been found to be different in both cases thereby also indicating the non-validity of Onsager's reciprocity relation.
Relative viscosities for the solutions of oxalic acid and its salts, viz. ammonium oxalate, sodium oxalate and potassium oxalate, at different concentrations have been determined in water and in binary aqueous mixtures of tetrahydrofuran (THF) [5, 10, 15 and 20% by weight of THF] at 298⋅15 K, and in water and in 5% (w/w) THF + water at five different temperatures. The data have been evaluated using the Jones-Dole equation and the obtained parameters have been interpreted in terms of solute-solute and solute-solvent interactions. The activation parameters of viscous flow have been obtained which depicts the mechanism of viscous flow. The oxalic acid and its salts behave as structure breakers in water and in binary aqueous mixtures of THF.
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