One of the properties that helps characterize a substance is its molar mass. If the substance in question is a volatile liquid, a common method to determine its molar mass is to use the ideal gas law, PV = nRT. Because the liquid is volatile, it can easily be converted to a gas. While the substance is in the gas phase, you can measure its volume, pressure, and temperature. You can then use the ideal gas law to calculate the number of moles of the substance. Finally, you can use the number of moles of the gas to calculate molar mass.


In this experiment, you will

  • Evaporate a sample of a liquid substance and measure certain physical properties of the substance as it condenses.
  • Determine the molar mass of an unknown liquid.