Problem: In the Dumas-bulb technique for determining the molar mass of an unknown liquid, you vaporize the sample of a liquid that boils below 100 oC in a boiling-water bath and determine the mass of vapor required to fill the bulb (see drawing ).From the following data, calculate the molar mass of the unknown liquid: mass of unknown vapor, 1.013 g ; volume of bulb, 354 cm3 ; pressure, 743 torr ; temperature, 99 oC .

🤓 Based on our data, we think this question is relevant for Professor Holler & Pietrovi's class at UPENN.

FREE Expert Solution

Recall that molecular weight is in grams per 1 mole of a substance.

$\boxed{\mathbf{M}\mathbf{o}\mathbf{l}\mathbf{e}\mathbf{c}\mathbf{u}\mathbf{l}\mathbf{a}\mathbf{r}\mathbf{ }\mathbf{W}\mathbf{e}\mathbf{i}\mathbf{g}\mathbf{h}\mathbf{t}\mathbf{ }\mathbf{\left(}\mathbf{M}\mathbf{W}\mathbf{\right)}\mathbf{=}\frac{\mathbf{g}}{\mathbf{m}\mathbf{o}\mathbf{l}}}$

First, we have to calculate the amount of gas in moles using the ideal gas equation.

$\boxed{\mathbf{P}\mathbf{V}\mathbf{=}\mathbf{n}\mathbf{R}\mathbf{T}}$

P = pressure, atm
V = volume, L
n = moles, mol
R = gas constant = 0.08206 (L·atm)/(mol·K)
T = temperature, K

Isolate n (number of moles of gas):