Molar mass of a gas


background [prelab assignment (10 points) due at the beginning of the lab]

design an experiment to determine the molar mass of a gas

sketch a data table for this lab containing entries for all required experimental measurements  (i.e. reveiw purpose & content of lab report)



determine the molar mass of a gas using a 50 versus 125 mL flask

does the size of a flask affect the accuracy of determining the molar mass of a gas ?


balance, flask (50 or 125 mL), aluminum foil, ice, graduated cylinder

Bunsen burner, beaker, water, pressure & temperature probe; metal ring, ring stand

~ 1 mL hexane or cyclohexane for both flasks

methods / data analysis

student design [hint:  see textbook problem 10.37]

other comments

water bath temperature < 90 °C; do not boil

wipe underside of aluminum foil after water bath incubation / prior to measuring its mass


Content of lab report [ 20 points]

data analysis  (10 points)

data table of your experimental measurements

determination of the molar mass of the gas - based on your group's data (show your work)

statistical analysis of class data  (see purpose; include interpretation of p-value)

error analysis  [10 points]

calculate % error

describe 2 pausible / nontrivial experimental errors & rationalize its effect on your determination of the molar mass of a gas


lab activity source (examples):  site 1  [access 4 / 2009]