February 21, 2017

Homework Help: AP Chemistry

Posted by D on Thursday, November 4, 2010 at 4:52am.

The molar mass of a volatile liquid (one which vaporizes easily) can be determined by a the DUMAS METHOD.' In this process a small amount of the liquid (a few drops) is placed in a clean flask. The mouth of the flask is covered with a piece of foil that has a small hole (pin hole) in it. The flask is heated in a boiling water bath until the liquid vaporizes completely. The air in the flask (and the excess vapor) escapes through the pinhole leaving the flask filed with the vapor. When the flask cools the vapor condenses and can be massed along with the flask. In this way the volume of the vapor (volume of the flask),temperature of the vapor(temperature of the water bath) pressure of the vapor (atmospheric pressure) and mass of vapor (mass of flask and condensed vapor minus the mass of the empty flask) can be determined. The molar mass of the gas can then be determined using the formula from this lab. Suppose that the original few drops of liquid added to the flask contained a nonvolatile (will not vaporized) contaminate. WHAT effect (if any) would this have on the experimentally determined molar mass of the liquid?

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