1. Physical chemistry experiment
Dr. Wenfeng Han

2. Physical chemistry experiment
It’s important to understand the theory and procedure before experiment.
Following the instruction and recording all the data .
Prepare the report on your own. Don’t Copy others!
After experiment, show your data to me and leave the lab upon approval.
Two students as a team.
I will collect your reports during next experiment.
Experiment handouts and report:

3. Experiments 4 Vapor Pressure of a Pure Liquid

4. Experimental objectives
1. Relationship between vapor pressure and temperature
2. Run a vacuum apparatus.

5. 1. Vapor pressure Lnp vs. 1/T ----straight line its slope =？
the equilibrium gas phase
A(l) ↔ A(g)
Clapeyron-Clausius equation
Lnp vs. 1/T ----straight line
its slope =？

6. Relationship of p –T Control the pressure-----Vacuum system(pump)
Vacuum pump
Manometer
Buffer
Two-way valve
Temperature (heater, thermometer)
Power source
Stirrer
Output voltage of power source
Sample (pure water)

7. 2. Apparatus Feeding Manometer Condenser Two-way valve Equilibrium
chamber
Thermometer
Two-way valve
Liquid riser
Feeding
Vacuum pump
Magnetic bar
Heater
Buffer
Power source
Magnetic stirrer

8. Experimental procedure
Turn on the manometer
Leak test
Vacuum the system to around -45 kPa and wait for 5 min. If the change of reading is less than 0.25 kPa.
c) Switch on the cooling water for the condenser.
d) Switch off Valve 13，and turn on the pump, turn on Valve 13 slowly vacuuming the system to -42 to -43 kPa. .

9. Experimental procedure
e) Tune the stirrer to a suitable stirring rate (Do not stir too vigorously).
f) Adjust the output voltage of power source (There is a black mark for proper output volt).
g) After water boils, adjust the output voltage to get a condensation rate in condenser 7 of 6~10 drops/min. When the temperature (Thermometer 4) maintain stable, record the temperature and the corresponding vacuum pressure (manometer 14).
h) Increase the pressure in the system by 3-5 mmHg (around 6 kPa) by allowing a small amount of air to enter through tap B slowly. As the pressure in the system increases, boiling will stop. It is now necessary to increase the heating to start the boiling again. Record the new boiling point and the corresponding pressure.

10. Data analysis The pressure of the system
P = Atmospheric pressure – Reading of manometer
The atmospheric pressure is read directly on a Fortin Barometer.
Viscosity determination
Compare your determined viscosity with literature value and calculate the experimental error.

11. Calculate the enthalpy of vaporization of water
Plot ln P versus 1/T.
The unit of temperature should be in Kelvin!!!
Calculate the enthalpy of vaporization of water
The standard evaporation heat of water: