Molecular Weight of Acetone
Name ______________________
Introduction: All gases take up the same volume at equal temperature and pressure. If we know how
many moles of a gas are present and the weight of that gas, we can then know the molar mass of that
gas.
In a nutshell, we will be attempting to find the molar mass of acetone. To do this, we will place a few mL
of acetone into a 250 – 500 mL flask. We will place an aluminum foil seal on the flask with a tiny
pinhole. We will then gently heat the acetone to make it evaporate. The idea is that as gas effuses
through the pinhole, the flask will fill with pure acetone.
Procedure
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Place a few mL of acetone in a 250 – 500 mL flask.
Cover flask with aluminum foil
Make a pinhole with a tack or other device in aluminum foil
Gently heat acetone and flask
When all the acetone is evaporated, remove flask from heat and start to cool flask to 0 C
Determine the mass of liquid (acetone) which reforms.
Calculations
1. Determine the amount of moles of gas that would occupy your flask at approximately 40 C
(approximated temperature of interior of flask).
2. Using a proportion, determine how what the mass of 1.0 moles of acetone would have.
Further practice
1. A certain gas occupies a volume of 350 mL at a temperature of 0 C and 1 atm. If the gas has a
mass of 1.2 g, what is the molar mass of the gas?
2. A certain gas occupies a volume of 1.0 L at a temperature of 0 C and 1 atm. If the gas has a mass
of 2.0 g, what is the molar mass of the gas?
3. A certain gas occupies a volume of 500 mL at a temperature of 40 C and 1 atm. If the gas has a
mass of 1.4 g, what is the molar mass of the gas?