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does anyone know how to apply the ideal gas law?
Use these date to calculate the molar mass of an unknown volatile liquid. (this is all i was given)
Initial mass of empty flask and top= 86.8234 g
Final mass of flask, top and condensed liquid= 87.7431 g
Flask Volume= 274.0 mL
Barometric Pressure= 741.6 torr
Temperature= 99 C
What is the Molar Mass?
2 Answers
- Chem ManLv 710 years agoFavorite Answer
Ideal Gas Law: PV = nRT
Using the ideal gas law, first find the number of moles, n; then divide the mass by the moles to get the molar mass.
Convert P to atm, V to liters, and T to kelvins when using R = 0.08206 L atm / K mol
741.6 torr x (1 atm / 760 torr) = 0.976 atm
274.0 mL x (1 L / 1000 mL) = 0.2740 L
K = C + 273 = 99 + 273 = 372 K
PV = nRT
n = PV / RT
n = (0.976 atm x 0.2740 L) / (0.08206 L atm / K mol x 372 K) = 0.00876 mol
molar mass = g/mol = (87.7431 - 86.8234) g / 0.00876 mol = 105 g/mol
- ChrisLv 710 years ago
One warning: Is the "empty" flask truly empty (i.e. evacuated) or is it filled with air? If it is filled with air, then a simple subtraction only tells you how much more the vapour weighs than the same volume of air. This may be important, especially if you are going for 4 sig figs.
If the flask was evacuated, the molar mass calculates to 105.1 g/mol
