The effect of salt and temperature on the infinite dilution activity coefficients of volatile organic chemicals in water

We have measured the infinite dilution activity coefficients for five volatile organic compounds (dichloromethane, chloroform, 1,2-dichloroethane, trichloroethylene and benzene) in aqueous salt solutions over the temperature range of 10°C to 40°C, and sodium chloride concentrations from 0 to 2.5 M using headspace gas chromatography. These data were easily fit as a function of salt concentration using the Setschenow expression, and as a function of temperature. By taking derivatives of the fitted data as a function of temperature, one obtains estimates of the partial molar excess enthalpy and entropy at infinite dilution of the organic chemicals as a function of temperature and salt concentration.