Construct a Pressure-Composition Diagram for Immiscible Liquids

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This Demonstration leads you through a step-by-step procedure to create a pressure-composition diagram for two immiscible liquids (water and an organic compound) at a fixed temperature. The organic can be benzene, toluene or -hexane. In each step, drag a line or point to make a guess and then check the "solution" box to show the correct answer. You can only move forward or select "new problem" to start over at a different temperature and a different organic. For any step, check "hint" for help.

Contributed by: Rachael L. Baumann (March 2018)
Additional contributions by: John L. Falconer
(University of Colorado Boulder, Department of Chemical and Biological Engineering)
Open content licensed under CC BY-NC-SA



Immiscible components do not mix in the liquid phase, and each independently exerts its saturation pressure and ; the subscripts and refer to benzene and water. The equations are the same for the other organics (toluene, -hexane). The total pressure above the two immiscible liquids is equal to the sum of their saturation pressures:


The saturation pressures are calculated using the Antoine equation:


where is the saturation pressure of (bar); , and are Antoine constants; and is temperature (°C).

For the benzene-water system, for conditions where benzene condenses, the dew point curve is:


where is the mole fraction of benzene in the vapor phase.

For conditions where water condenses, the dew point curve is:


where is the mole fraction of water in the vapor phase and .

The screencast video at [1] explains how to use a similar Demonstration.


[1] Immiscible Liquids on Pressure-Composition Diagram [Video]. (Feb 1, 2018)

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