1. Experiment 9. Liquid-Vapor Equilibrium in a Binary System The vacuum manifold used in this experiment is shown here. The main stopcock isolates the system from the pump, which is further protected from the gaseous reagents by a cold trap filled with liquid N 2. The MKS Baratron pressure gauge converts pressures in Torr to voltages (100 Torr = 1 V), which are read on a voltmeter. The sample cell containing liquid is attached at the middle connector. The gas in equi-librium with the liquid is captured in the large bulb and is later condensed into a second sample cell attached to the connector at the far right. (These are illustrated in more detail on the next page.) The stopcock at left is used to bleed air into the system at the end of the experiment.

2. 2 The region of the cells and collection bulb is shown here in larger scale. The liquid sample cell is immersed in an ice water bath for final equilibrium measure- ments. Make a rough determination of the equilibrium P before opening the stopcock to the collection bulb. After this P value is known, open the stopcock to the bulb to begin collecting vapor, and remove the ice bath. This removal will offset the cooling of the liquid due to the large amount of evaporation and will speed up the collection process. When P is near the equilibrium value, reinstall the ice bath to achieve final equilibrium. After this, close the sample cell stopcock and move the gas to the other cell by freezing it there with liquid N 2.

3. 3 Even with this procedure, it can take ~20 min to carry out all the operations needed to obtain the equilibrium pressure and samples of liquid and gas present at equilibrium for a single starting sample. Thus, teams should plan ahead so that they are able to begin the work on the vacuum line as soon as possible during the period. Start with pure acetone and pure chloroform, for which no gas need be collected. Then go to the first mixture as soon as it has been prepared. One or two partners should manage the vacuum line work while the other(s) prepare mixtures and read refractive indices on the refractometer. In this way you should be able to obtain pressure and composition data for the two pure substances and at least six mixtures. Do more only if time permits. (However, you should obtain calibration data for at least 10 mixtures and the two pure components.)