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!