SOLUTION BEHAVIOR OF SODIUM DODECYL-SULFATE IN METHANOL

The electric conductivities of sodium dodecyl sulfate (SDS) in methanol and water were measured at 298 K in a concentration range up to 10 mmol dm-3. The values of the limiting molar conductivities of SDS, LAMBDA-0, in methanol and water were estimated to be 81.5 and 74.0 S cm2 mol-1, respectively, and compared with each other. From those values and the values of NaCl in both solvents, the limiting molar conductivities of dodecyl sulfate ion in methanol and water were estimated to be 36.27 and 23.90 S cm2 mol-1, respectively. Also, the vapor-pressure depression of SDS in methanol was measured at 298 K in the concentration range up to 42 mmol kg-1. From the results, and according to the theory regarding strong electrolytes, the mean ionic activity coefficient, gamma+/-, of SDS in methanol at 298 K was calculated. Further, the solubility and heat of solution of SDS in methanol at various temperatures and at 298 K, respectively, were measured. From a thermodynamic analysis of these results, the theoretical relation between 1n gamma+/- and m was obtained over the range of temperatures 285-295 K.