Lab: Determination of the Molar Mass of Butane
Problem: To determine the molar mass of butane and compare it to the accepted value.
Procedure:
1. Obtain a lighter and make sure it is dry by shaking it a few times. Do NOT remove the clay from
the lighter.
2. Determine the mass of the lighter to the nearest .01g and record in data table.
3. Completely fill a 100mL-graduated cylinder with water and invert it in the tub of water so that no air
bubbles are present.
4. Hold the butane lighter under the opening of the cylinder under the water and release the lever.
Continue to fill the cylinder with butane until the gas level can be made equal with the outside
water level. BE CAREFUL NOT TO FILL PAST THE MARKINGS ON THE GRADUATED
CYLINDER.
5. Read the volume of the butane to the nearest .1 mL and record on data table.
6. **Use dimensional analysis to convert the measured volume to Liters and record in data table.
7. Dry the lighter by carefully shaking off all water and “dabbing” with a paper towel if necessary. Do
NOT remove the clay from the lighter. Determine the mass of the lighter after lab and record in
data table.
8. **Calculate the grams of butane used and record in data table.
9. Take the temperature, to the nearest .1°C of the water and record in data table.
10. **Convert to Kelvin and record. (We are assuming that the water temperature is the same as the
butane temperature.)
11. Record the current atmospheric pressure, in “in. of Hg” (provided by teacher) in your data table.
12. **Use dimensional analysis to convert the atmospheric (air) pressure, in “in. of Hg” to “mm of Hg”.
Record the “mm of Hg” value in data table.
13. Look up the temperature on the water vapor pressure chart provided by your teacher and record
the vapor pressure, in “mm of Hg” in the data table.
14. **Calculate the pressure of the butane, in “mm of Hg”.
15. **Use dimensional analysis to convert the pressure of the butane from “mm of Hg” to “atm”.
Record the pressure of butane, in atm, in data table.
16. Record the value for R in your data table.
17. **Using your values for P, V, T of butane and R, calculate the number of moles (n).
grams
18. **Knowing that molar mass is
calculate the molar mass of butane. Record answer in data
mole
table as “experimental value”.
19. The formula for butane is C4H10. To calculate the true molar mass of butane, find the mass of carbon and hydrogen
on the periodic table. Then, multiply the mass of carbon by 4 and hydrogen by 10. Add your answers. (4 x 12.011g)
+ (10 x 1.008g) = 58.124 g. Since our balances go to the hundredths place, round to 58.12 g.