Molar Mass of Butane Lab
Purpose: To experimentally determine the molar mass of butane gas (C4H10) using the
Ideal Gas Law and Avogadro’s Principle.
Materials:
butane lighter
eudiometer tube
electronic balance
thermometer
large tray
1000mL beaker
hair dryer
Procedure:
1. Mass the lighter to the nearest 0.001g.
2. Fill the eudiometer completely with tap water. Also fill the yellow tray will tap
water. The tray does not need to be completely full.
3. Fill a 1000mL beaker nearly full with tap water. This will be used to equalize the
pressure inside the eudiometer to the atmospheric pressure.
4. Place the eudiometer in the water, open end down. Do not allow any air to enter
the tube.
5. Hold the lighter under the eudiometer making sure that the opening which the gas
is expelled is directly below the opening of the tube. Press the tab on the lighter
to begin filling the tube with butane gas. Continue to fill with butane until the
eudiometer contains between 47.0 and 49.9mL of butane gas.
6. Place your finger over the end of the tube and remove it from the tray of water.
7. Place the tube into the 1000mL beaker of water and match the levels of water in
each container. Remember that this must be done to equalize pressures. Once the
levels are equal, read the eudiometer to the nearest 0.1mL.
8. Completely dry the butane lighter by first shaking the water from the lighter and
then drying it with the hair dryer. Be careful not to overheat the lighter. This is a
critical step! The lighter must be completely dry.
9. Mass the lighter to the nearest 0.001g.
10. Note the barometric pressure, room temperature, and the temperature of the water
in the tray for the current trial.
11. Repeat the procedure in order to obtain a total of three trials.
Data Sheet
Trial 1
Trial 2
Trial 3
Mass of lighter before
collection
Mass of lighter after
collection
Mass of butane gas
expelled
Volume of gas produced at
room temperature/pressure
Barometric Pressure
Room Temperature
Water Temperature
Vapor pressure of water at
water temperature
Partial pressure of butane
Pbutane = Pair – PH2O
Moles of butane produced
Molar mass of butane
(mass of butane/ moles)
Theoretical Molar Mass of Butane (from periodic table) = ___________________
1. Using the Combined Gas Law, calculate the volume that the expelled gas would
have at STP. Make sure to convert your answer to liters.
2. Use Avogadro’s Principle to determine the number of moles of butane at STP.
3. Divide the mass of butane expelled by the number of moles calculated from #2.
How does this compare to your molar mass obtained in the last step of the data
table?