MOLAR MASS OF BUTANE LAB (Guidelines: 1,2,3,7,9,10,11,12)
PURPOSES: To use the Ideal Gas Law to determine the molar mass of an unknown gas.
To do stoichiometry calculations involving gases
PROCEDURE: As described by your instructor
DATA:
mass of lighter before gas collection
mass of lighter after gas collection
mass of butane collected
__________g
__________g
__________g
volume of gas (1st collection)
volume of gas (2nd collection)
volume 1 + volume 2
_________mL
_________mL
_________mL
Temperature
_________C
Barometric Pressure
Vapor Pressure of water at observed temp.
Pressure of Butane (barometric – vapor)
_____mm Hg
_____mm Hg
_____mm Hg
CALCULATIONS / QUESTIONS:
1. Convert the total volume of gas collected from mL to Liters.
2. Convert temperature from C to K.
3. Convert the pressure of the butane from mmHg to atm.
4. Calculate the total number of moles of butane gas collected using the ideal gas law.
5. Calculate the molar mass of butane. (Hint: remember that the units on molar mass are grams/mole)
6. When determining the pressure of the butane, why was it necessary to subtract the
vapor pressure of water from the barometric pressure of the atmosphere?
THE FOLLOWING QUESTIONS REFER TO THE BURNING OF THE BUTANE COLLECTED IN THE
GRADUATED CYLINDERS
7. Write a balanced equation for the combustion of butane.
8. Use the stoichiometry road map presented in class to calculate the following
(assuming the reaction took place at STP):
a) the number of liters of oxygen gas which reacted
b) the number of liters of carbon dioxide gas formed
c) the number of grams of water formed
BEGIN ALL STOICHIOMETRY CALCULATIONS WITH THE NUMBER OF GRAMS OF
BUTANE WHICH YOU COLLECTED.
9. What was the limiting reactant -- the butane or the oxygen? Explain.
ERROR ANALYSIS:
The actual molecular formula of butane is C4H10. Calculate your percent error for your molar mass calculation
in calculation #5.
CONCLUSION:
Don’t forget to write a concise and complete conclusion!