A student weighs an empty flask and stopper and finds the mass to be 55.844 g. S
ID: 607192 • Letter: A
Question
A student weighs an empty flask and stopper and finds the mass to be 55.844 g. She then adds about 5 mL of an unknown liquid and heats the flask in a boiling water bath at 99.7 degrees C. After all the liquid is vaporized, she removes the flask from the bath, stoppers it, and lets it i s cool. After it is cool, she momentarily removes the stopper, then replaces it and weighs the flask and condensed vapor, obtaining a mass of 56.101 g. The volume of the flask is known to be 248.1 mL. The barometric pressure in the laboratory 752 mm. Hg. a. What was the pressure of the vapor in the flask atm? P = ______ amt b. What was the temperature of the vapor in K? the volume of the flask in liters? T =______K, V=______ L c. What was the mass of vapor that was present in the flask? g = ___________grams d. How many moles of vapor are present? n =___________grams e. What is the mass of one mole of vapor? MM=___________g/moleExplanation / Answer
flask = 55.844g
5ml liquid at 99.7ºC
mass flask after heating = 56.101g
volume flask = 248.1ml
p = 752mm
p = 752mm of hg (1 atm/760 mm of hg) = 0.989 atm
mass gas = 56.101g - 55.844g = 0.257g
t in K = 372.85K, v = (248.1/10^3ml) = 0.2481 L
n = pv/rt = (0.97atm x 0.2481L) / (0.0821L-atm/mole-K x 372.85K) = 0.796595422 moles
mass 1mole gas = 0.257g / 0.796595422 moles = 0.000322622994 kg / mol
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