The mass of the Florence flask + stopper + air used in the molecular weight dete
ID: 1063921 • Letter: T
Question
The mass of the Florence flask + stopper + air used in the molecular weight determination experiment was 117.007 g. Seven milliliters of an unknown volatile liquid was transferred into the Florence flask. A one-hole stopper was placed on the flask and the flask was then placed in a hot water bath. As soon as all the unknown liquid was vaporized over a barometric pressure of 759 torr, the flask with the one-hole stopper was taken out of the 91 degree C water bath and the one-hole stopper was replaced with a stopper. The mass of the Florence flask + stopper unknown gas (after cooling) was found to be 117.435 g. At the end of the experiment, the Florence flask was filled with water and its volume was found to be 272. mL. What is the mass (in g) of the air (d = 1.18 g/L) in the Florence flask? What is the mass (in g) of the unknown gas? What is the molecular weight (in g/mol) of the unknown?Explanation / Answer
For the given experiment
a) mass of air in the flask = 0.272 L x 1.18 g/L
= 0.321 g
b) mass of unknown gas = 117.435 - 11.007
= 0.428 g
c) molecular weight of unknown gas = 0.428 x 0.08206 x (273 + 91)/(759/760)(0.272)
= 47.063 g/mol
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