Title: Molar Mass of liquid through Vapor Density
Joshua Bryant
Period 2
9/8/10
A.P. Chemistry
Purpose: Determine the molar mass experimentally of an unknown liquid through
the vapor-density method.
Procedure:
First, I placed a beaker filled with 200 milliliter of water on a hot plate to
start boiling the water.
Next, I obtained the mass of the empty flask.
We then arranged the flask with the foil loosely wrapped around the top,
with the rubber band holding it in place. With the pin, I punched a small hole in the
top of the aluminum foil.
I then removed the aluminum foil cover and placed approximately 2 to 3
milliliters of the unknown liquid in the flask.
I then replaced the aluminum foil and the rubber band.
I then placed the flask in a water bath, holding it in place with a clamp.
I allowed for all of the liquid in the flask to vaporize, including any that has
condensed on the sides or the underside of the aluminum foil.
While the water was boiling, I recorded the temperature and the atmospheric
pressure.
When all of the liquid was vaporized, I removed the flask from the water bath
and paced it on the table to cool for 5 to 10 minutes. I then placed the flask in an ice
bath.
I then wiped the flask completely dry and removed the aluminum foil before
calculating the mass of the liquid inside the container.
I then poured the liquid into the waste jar, and filled the flask completely
with water. I finally measured the volume of the flask by pouring the water inside
the container into a graduated cylinder.
Data Analysis:
The recorded values for:
 Pressure = 1 atm
 Volume = 0.142 L
 Temperature = 374.15 K
 Mass of empty container = 97.8 g
 Mass of container with condensed gas = 98 g
 Mass of liquid left in container = 0.2 g
The number of moles is calculated with the formula
where n is the
number of moles, P is the pressure in atmospheres, V is the volume, T is the
temperature, and R is the Universal gas constant of 0.0821 Latm/molK.
Joshua Bryant
Period 2
9/8/10
A.P. Chemistry
After accounting for sig. figs., the molar mass of the unknown liquid is
430 g/mol.
Conclusion: The molar mass of the unknown liquid is 430 g/mol. I also believe the
unknown liquid to be some form of acetone