Determination of the Vapor Pressure Curve of a Liquid in the Presence of a Nonvolatile Solute

We present a modification of the data analysis for the classical physical chemistry experiment Determination of Enthalpy of Vaporization by the Boiling-Point Method. The vapor pressures of solutions of both ionic and molecular compounds are determined at different temperatures. In this experiment we show that the enthalpy of vaporization change is dependent on the type and amount of nonvolatile solute present. Sets of data collected for different concentrations of sodium chloride, urea, and sucrose solutions are analyzed in order to determine H_vap and S_vap for pure water and for solutions of ionic and molecular solutes.Students perform the data analysis taking into consideration the activity coefficient for the solution and the mole fraction of the solvent. Simultaneous data analysis is introduced and results are used to explain the meaning of the physical parameters determined using this method of data analysis.