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For the Dumas Method of determining Molar Mass of Volatile Liquids?
... How do I determine whether a particular volume of volatile liquid is sufficient to determine its molar mass?
For example, 4.00 mL of methanol and its density is 0.796 g/mL at 392 K, 1.037 atm, flask has a volume of 150 mL.
I'm pretty sure that when the gas evaporates and fills the entire flask, there must be enough gas to do so. How do I prove this?
2 Answers
- 1 decade agoFavorite Answer
I think what you should do is use the given density and volume to determine the mass, and since it is of methanol, you can find the molar mass of it and then find the number of moles.
Once you have the moles you can use the rest of the information that you have been given to calculate the volume of methanol at that temperature via the ideal gas law assuming that methanol behaves like an ideal gas.
density = mass / volume
mass = density x volume
mass methanol = 3.184 g
molar mass methanol (CH4O) = 32.04 g/mol
moles = mass / molar mass
moles methanol = 0.09937 mol
PV=nRT
V = (nRT) / P
V = (0.09937 mol x 0.082054 atm L/ K mol x 392 K) / 1.037 atm
V = 3.0 L
since 3.0 L > 150 mL you have enough to fill the flask at these conditions.
Well, in my opinion, but I could be wrong. Just go ask the T.A.
