CHEMISTRY/EXPERIMENT
USING THE IDEAL GAS EQUATION
In this experiment a sample of butane gas will be collected from a commercial lighter by the water
displacement method. After correcting the data for a dry sample of the gas, the molar mass of butane can be
calculated by using the ideal gas equation PV = nRT.
PROCEDURE:
1. Record the room temperature, in degrees Celsius.
2. Obtain a bucket with room temperature water.
3. Place a lighter under water in the bucket. Remove the lighter, shake off the water, and dry the outside
with a tissue. Determine the mass of the lighter to the nearest 0.01 gram. Record.
4. Completely fill a 100 mL graduated cylinder with water and invert in the bucket. Be careful not to let
any air into the cylinder.
5. Release the butane gas from the lighter by pressing the small lever near the flint wheel. Release the
gas under water being careful that all of the butane is collected in the graduated cylinder by water
displacement. Release enough gas to fill the graduated cylinder between 80-90 mL.
6. Allow the butane to reach room temperature (about 5 minutes). Adjust the level of the water inside
and outside the graduate until they are the same by raising or lowering the cylinder in the bucket.
With the pressure so equalized with atmospheric pressure, read the volume of the gas collected using
the cylinder's graduations (to the nearest 0.5 mL). Record.
7. Remove the lighter from the bucket. Shake off any excess water, and dry with a tissue. Measure and
record the mass of the lighter.
IDEAL GAS EQUATION WRITE-UP
PURPOSE: The purpose of this experiment is to determine the molar mass of butane gas using
the ideal gas equation and to compare the experimental value with the theoretical value from the
periodic table.
DATA:
758
mm Hg
2.2
grams
grams
mL
kPa
K
kPa
------------------L
----------
1. Conversions: (Show calculations and add to table above.)
°C to K
mm Hg to kPa
mL to L
Temp (room)
Pressure (Proom)
Mass lighter(before)
Mass lighter(after)
Volume butane
Vapor press water (PH2O)
°C
ANALYSIS/CALCULATIONS:
2. Mass of butane used: (show calculation with complete units)
3. Partial pressure of dry butane: (Show calculation) Pbutane = Proom - PH2O
4. Use the ideal gas law equation to solve for the number of moles of butane. Use R = 8.31
L kPa
mol K (Use partial pressure of butane, from #3, as pressure.)
5. Determine the experimental molar mass of butane, using data from above calculations. (Do
not use the periodic table) Remember molar mass = g/mol
CONCLUSION/QUESTIONS:
1. Butane has the formula C4H10. Use values from periodic table to determine the theoretical molar mass of
butane.
2. Calculate the % error between your experimental value and the actual molar mass of butane.
3. Can the same experimental techniques be used to determine the molar mass of all gases? Explain. Hint: What if the
gas were soluble in water?