Chemistry - Gas Stoichiometry

Question

A laboratory group measures an excess of a volatile liquid. They add this to an empty flask with a volume of 345 mL. They heat the sample to 88.4 degrees Celcius until all the liquid is vaporized. The pressure in the lab is 0.987 atm. If 0.270 grams of volatile liquid were left in the flask, what was the molar mass of the compound?

Answer 1

Volume = V = 345 ml = 0.345 L

Temperature = T = 88.4ºC + 273.15 = 361.55K

Pressure = P = 0.987 atm

moles = n = ?

Gas constant = R = 0.0821 Latm/Kmol

Use the ideal gas law and solve for moles (n)

PV = nRT

n = PV/RT

n = (0.987)(0.345) / (0.0821)(361.55)

n = 0.01147 moles

Molar mass = g / moles

Molar mass = 0.270 g / 0.01147 mols

Molar mass = 23.5 g / mol