A large boiling water bath is prepared. A clean and dry 250-mL flask is fitted with a small piece of aluminum foil with a small vent hole; and this assembly is massed. About 4 mL of a volatile liquid suspected of being isohexane (C4H14) is added to the flask and the foil carefully replaced. The flask is then submerged in the boiling water up to the bottom of its neck and the volatile liquid is allowed to boil away. The flask is then quickly cooled to room temperature so the vapor of the volatile liquid can condense in the flask. The outside of the flask with the condensed liquid is then carefully dried and massed. The flask is then emptied and compleltly filled with deionized water, the foil is replaced, and the entire assembly remassed.
A.) Use the data given below to calculate the molar mass of the volatile liquid.
B.) If the volatile liquid is in fact isohexane, what is the percent error in this experiment?
MASS OF EMPTY FLASK WITH FOIL…185.865g
MASS OF FLASK, FOIL, CONDENSED LIQUID…186.616g
MASS OF FLASK, FOIL, WATER…454.917
TEMPERATURE OF WATER BATH…99.6 degrees C
ROOM TEMPERATURE…22.6degreesC
TEMPERATURE OF WATER…26.3degreesC
ATMOSPHERIC PRESSURE…746.8 Torr
And, in case you don’t have it memorized, the molar mass of gas=DRT/P. Thanks everyone!
I suspect you pretty much know how to carry out this calculation.
Why not post your answer and workings, and see if we agree?
That way it wouldn’t seem like you’re simply being lazy.
If you have no idea how to perform the calculation, go see your TA and start paying attention in class!!!
My god, I sound like my father!
Alright, let me show you what I got…
the mass of the wather= 269.301
the density of water at 26.3 (26) is .996814
therefore the volume of the water is .270162 L
the volume of the gas is the same as the volume of water
the mass of the gas = .751 g
therefore the density of the gas=.27798 g/mL
But then when I try to put this information into the gas equation, the answer is obviousily wrong. I know I must be missing something very obvious.
Mm= (.27798 X .0821 X 299.5)/.9826 which equals 6.956.
This is definitly not right, since hte molar mass of isohexane is 86.2.
Your density of the gas is incorrect and you are using the wrong temperature. The gas exists at 99.6 C.
Remember the unit on the gas constant R is atm L/(mol K). You need to include the units in your calculation not just plug in numbers. You probably did this on paper and not in your post. Your units will also tell you if you did something wrong.