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Vapor Pressure Lab
- Vapor pressure is the pressure exerted by the vapor particles (in the gas phase) above a liquid layer (the system must be closed, in other word, the container is sealed).
- Vapor pressure is directly related to the intermolecular force (IMF) keeping the liquid molecules held together. Therefore, the higher the IMF, the less amount of vapor particles are in the gas phase, and therefore, the lower the vapor pressure.
Boiling point is a function of IMF and MW, molecular weight or molar mass.
- Boiling point is the temperature where the vapor pressure = atmospheric pressure.
- In this lab, we will look at the intermolecular forces in the substance to predict which substance has the highest vapor pressure (thereby determining which has the greater boiling point).
At your desk, determine the molecular polarity of hexane (C6H14) and water.
In the lab
- Get a test tube rack and two large test tubes.
- Get two large balloons (do not do anything with balloons especially blow them up)
- Get a 250ml beaker and fill it with approximately 150ml of tap water.
- Turn on heating element and place 250ml beaker on heater.
- In one large test tube, add approximately 2ml (w/pipette) of hexane and then place balloon over top of test tube making sure to take all air out of balloon.
- In the other large test tube, add approximately 2ml (w/pipette) of water and then place balloon over top of test tube making sure to take all air out of balloon.
- Make observation of the condition of the balloon.
- Let heating element heat up the water bath & both of the test tubes (once boiling starts shut off heating element). Periodically, make observations on the condition of the balloons.
- When done heating system, remove (once beaker is cool to touch) the 250ml beaker with test tubes from the heating element and let it cool on the table top.
- Observe the condition of the balloons after the water has cooled back down to room temperature.
- Initial observation of balloons in water bath:
- Periodic observation of balloons:
- Final observation of balloon after cooling back to room temperature.
- Which substance has the higher vapor pressure and how did you know it?
- Did your results agree with what you predicted?