Question

A volatile organic liquid with known molecular weight is added to a vapor density flask which has a known volume. The flask is heated using a boiling water bath until all of the liquid has evaporated.
After heating for an additional 1 or 2 minutes, the flask is removed from the boiling water bath, corked, and cooled using a room temperature water bath. Predict the mass of condensed vapor.

Temperature of the hot water bath (ºC): 99.4

Volume of the flask (mL): 496.3

Molecular weight of the unknown (g/mol): 131.4

Barometer reading (mm Hg): 760.5

Calculate the mass of condensed vapor in g.

Answer 1

Answer: Mass of the condensed vapor is 21.35 grams.

Explanation: As a gas, the Ideal Gas Law can be used to determine how many mols there are in the flask on the conditions described in question.

Temperature in K: 273 + 99.3 = 372.4K

Pressure in mmHg: P = 760.5 mmHg

Volume in L: V = 496.3.$10^{-3}$ = 0.5 L

Universal Constant of Gases in mmHg: R = 62.36 L.mmHg.K⁻¹.mol⁻¹

PV = nRT

n = $\frac{PV}{RT}$

n = $\frac{760.5.0.5}{62.36.372.4}$

n = 0.1625

To determine the mass in grams:

n = $\frac{m}{M}$

m = nM

m = 0.1625.131.4

m = 21.35

On the conditions cited above, there are 21.35 grams of the unknown condensed vapor