Determine the molar mass of the liquid

Question

An organic chemist isolates a colorless liquid from a petroleum sample. He uses the Dumas method and obtains the following data:

Volume of flask, V = 213 mL

Mass of flask: 77.834 g

Mass of flask + gas = 78.416 g

Temperature: 100°C

a) Determine the molar mass of the liquid.

b) Give 2 assumptions of kinetic molecular theory of glass

Answer 1

mass of gas = mass of flask + gas - mass of flask = 78.416 g - 77.834 g = 0.5820 g of gas

PV = nRT

Assuming atmospheric pressure of 1 atm, we have the following:

n = PV/RT = (1 atm)(0.213 L) /(0.0821 Latm/Kmol)(373K)

n = 0.007 moles

Molar mass = g / mols = 0.5820 g / 0.007 moles = 83.14 g/mol = molar mass of liquid

Two assumption of kinetic molecular theory:

i) the gas particles are not attracted to each other, nor to the surroundings

ii) the average kinetic energy of the gas particles is proportional to the absolute temperature