Determining Molar Mass by Ideal Gas Law

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I. Abstract:

By manipulating the ideal gas law (PV=nRT), we will be determining the molar mass of an unknown volatile liquid. Heating a flask filled with an unknown, easily evaporated liquid will allow for measurements that can be taken to work out the ideal gas equation. This lab will require knowledge of basic equations used in chemistry. Using these equations, such as density and number of moles(n), we can substitute different values into the ideal gas law to manipulate it.

II. Materials:
250-mL Erlenmeyer flask
Needle or pin
Unknown liquid sample
1000-mL beaker
Hot plate
Utility clamp
Aluminum freezer foil
Hot mitt
Wire gauze with ceramic center
1000-mL graduated cylinder

III. Procedure:

1. Aprons and goggles on. Clean a 1000-mL beaker for use as a heating bath. Set the beaker on a hot plate and begin heating. 2. Clean and completely dry the Erlenmeyer flask.
3. Cut a square of aluminum foil to serve as the cover of the flask. Trim the edges so that it neatly covers the edge of the flask. 4. Weigh the empty flask with cover and record to as many sigfigs as possible. 5. Obtain your unknown liquid and record the ID #. Add 3-4 mL of the liquid to the flask. Re-cover the flask, making sure the edges are tightly crimped. 6. Punch a tiny hole in the foil cover with a needle or pin. 7. Heat the water in the beaker to boiling. Adjust the heat so that the water will remain boiling but will not splash. 8. Immerse the flask containing the unknown liquid in the boiling water so that most of the flask is covered. Clamp the neck of the flask. 9. Watch the liquid carefully. The liquid will begin to evaporate, and its volume will decrease. 10. When it appears that the flask is completely filled with vapor, continue heating for 1-2 minutes. Remove the flask from the bath using...
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