Vapor Pressure Lab Report

Abstract:

The goal of this lab is to determine the molar enthalpies and entropies of vaporization of 6 different pure liquids, one of which is unknown and to be determined based on these calculated values. The five known liquids are: water (from tap), ethanol, methanol, isopropyl alcohol, and cyclohexane. Using a condenser, a heat mantle, pump, ballast volume, thermometer, and a pressure gauge, an apparatus is set up to measure the boiling points of these liquids at pressures of 150, 300, 450, 600, and 730 torr (see Figure 1.0 for set up) Because the boiling point of a pure substance is the temperature at which the condensation rate is equal to the evaporation rate, these pressures become the vapor pressures of these liquids at the boiling point. Hence, the pressure can be expressed as a function of temperature. Therefore because the Clausius-Clapeyron equation can be expressed as a function of temperature, it is used to find the molar enthalpies of vaporization. The molar enthalpies of vaporization are determined to be 31900 ± 200 J/mol for cyclohexane, 42800 ± 200 J/mol for 2-propanol, 46000 ± 5000 J/mol for methanol, 40800 ± 300 J/mol for ethanol, 41900 ± 100 J/mol for water, and 26000 ± 2000 J/mol for the unknown that’s taken to be acetic acid.

Experimental Procedure:

Before the experiment can begin, the equipment must be set up as illustrated by Figure 1.0.

Figure 1.0 Apparatus set up for experiment

The order of which liquid is boiled does not matter. The procedure is the same for each of them except for that of cyclohexane, which the triple point must be determined by adjusting the pressure and temperature.

A few milliliters (measured with approximation) of the chosen liquid are place in the flask with boiling chips and connected to the condenser. The pressure is raised to each of the pressures, and the heat is adjusted until the liquid begins boiling. After a few minutes, the temperature stabilizes and this is temperature is recorded as the...