# molar mass ap chem

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molar mass ap chem
Jahzeel Morales
AP Chemistry
December 12, 2014
Determination of the Molar Mass of Volatile Liquids
Theory:
Molar masses, can be seen and used daily in chemistry. In this lab, the ideal gas law helps determine and evaluate the molar mass of gases and volatile liquids. The ideal gas law compares four properties of a gas which include pressure, volume, moles, and temperature. During this experiment, the moles would be unknown, in effect the student must use a substance mass divided by its molar mass. With this, the ideal gas law can be arranged in an equation fit for helping the student determine the molar mass of a gas.
Purpose:
The purpose of the lab is to find the average molecular weight of ethanol, acetone, and isopropanol.
Pre-Lab Questions:
Mass of empty pipet
1.557 g
Mass of empty pipet and condensed methyl alcohol
1.571 g
Mass of pipet and water
16.001 g
Mass of condensed methyl alcohol
.014 g
Mass of water in filled pipet
14.444 g
Volume of pipet
0.014483--> 14.444 g(1ml/0.9973 g/mL)(1L/1000mL)
Molar mass of methyl alcohol (experimental)
30.44 g/mol = (.014g)(0.082057)(372.65 K)/(.971 atm)(0.014483 L)
Molar mass of methyl alcohol (theoretical)
32.04 g/mol

2a. If only part of the pipet was immersed in boiling water, so the temperature in part of the pipet was less than that of the water bath, then the temperature and part of the pipet would actually be less than what was originally recorded. The temperature would be too high and would cause the molar mass to be calculated higher than it should be.
2b. If the mass of the condensed liquid was not determined quickly and instead the pipet was allowed to stand for a while before immersing it in room temp. water, and then massing the pipet, some vapor would escape before it is condensed. This would reduce the actual volume of the condensed liquid which would make the molar mass decrease.
Procedure:
Place a 600 mL beaker on the hot plate and add about 450 mL of water to the beaker, along with several boiling

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