We are asked to calculate the molar mass of the unknown vapor.

Given:

m = 0.847 g

V = 355 cm^{3 }= 0.355 L

P = 753 torr = 0.991 atm

T = 100 ^{o}C +273.15 = 373.15 K

R = 0.08206 L-atm/mol-K

The molar mass of a volatile substance was determined by the Dumas-bulb method. (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^{o}C in a boiling-water bath and determine the mass of vapor required to fill the bulb (see drawing ). The unknown vapor had a mass of 0.847
g, the volume of the bulb was 355
cm^{3}, pressure was 753 torr, and temperature was 100 ^{o}C.

Calculate the molar mass of the unknown vapor.

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