Overview
This lecture covers how to determine the molar mass of a volatile compound using the ideal gas law by collecting experimental data from a flask setup.
Experimental Setup
- The goal is to identify a volatile compound by calculating its molar mass using the ideal gas law.
- A boiling water bath is used to vaporize a measured amount of an unknown liquid in an Erlenmeyer flask.
- The flask is sealed with aluminum foil and a rubber band, with a small hole punctured to allow trapped air to escape.
Data Collection Steps
- Record mass of empty flask with foil and rubber band: 73.80 g.
- Measure and add 2 mL of the unknown liquid into the flask.
- Cover and seal the flask, then suspend it in the water bath (not submerged).
- Wait until the liquid is fully vaporized and condensation disappears.
- Record barometric pressure: 1.0 atm (El Paso).
- Record water temperature at vaporization: 85.1°C.
- After cooling to room temperature, weigh the flask with condensed vapor: 74.13 g.
- Determine flask volume by filling with water and measuring with a graduated cylinder: 147 mL.
Calculations
- Calculate the mass of gas: subtract empty flask mass from mass with gas (74.13 g - 73.80 g).
- Use the ideal gas law (PV=nRT) with collected data to calculate molar mass of the volatile compound.
Key Terms & Definitions
- Volatile Compound — a substance that easily vaporizes at relatively low temperature.
- Ideal Gas Law — the equation PV=nRT relates pressure, volume, moles, and temperature of a gas.
- Molar Mass — the mass of one mole of a substance (g/mol).
- Barometric Pressure — the atmospheric pressure at the experiment location.
Action Items / Next Steps
- Use recorded data to calculate the mass of the gas.
- Apply the ideal gas law to find the molar mass.
- Identify the unknown compound based on calculated molar mass.
- Review experimental procedure for lab report.