Diffusion coefficients for the liquid system: Ethanol-water



Measurements of the liquid diffusion coefficients over the complete range of compositions of the ethanol-water system at 25°C. have been carried out using the porous diaphragm technique with a magnetically-stirred and modified cell. Both the integral and differential coefficients agree very closely with the values reported by Hammond and Stokes, although an improved method of calculating the differential coefficients has been used. The limiting values at 0 and 100% concentrations differ somewhat from those previously reported. By means of an experimental investigation the work of Smith and Storrow on the same system has been shown to be in error. Analytical errors in calibration have been reduced to a probable error of ± 0.1%, although there is an average deviation of ± 2% for all experimental points relative to the best line drawn through them. The diffusion coefficients based on concentration as a driving force, show a minimum at 25 mole % ethanol, corresponding to the minimum for the relative decrease in volume on mixing and the maximum for the viscosity-composition curve. For the dimensionless Schmidt number, a very sharp peaking to a value of 7500 occurs at the same composition.