Isolating Glass Bulbs

Question

A chemist isolated a gas in a glass bulb with a volume of 255 mL at a temperature of 25.0 Celsius and a pressure (in the bulb) of 10.0 torr. The gas weighed 12.1 mg. What is the molecular mass of the gas?

Answer 1

PV = nRT

Solve for moles (n) = PV/RT

n = (10.0 torr)(0.255 L)/(62.36 Ltorr/Kmol)(298K)

n = 1.37x10^-4 moles

molar mass = grams/moles

grams = 12.1 mg x 1 g/1000 mg = 0.0121 g

moles = 1.37x10^-4 moles

molar mass = 0.0121 g/1.37x10^-4 moles = 88.3 g/mole