Question

A 0.465 g sample of an unknown compound occupies 245 mL at 298 K and 1.22 atm. What is the molar mass of the unknown compound?

Answer 1

Using the Ideal Gas Law
PV= nRT
PV = (m/Mr) RT The molar mass of the unknown compound is : 38.0 g/mol

Mr = mRT / PV =  0.465 g x 0.08206 L * atm * K⁻¹  mol ⁻¹ x 298 K / 1.22 atm x 0.245 L = 38.0 g / mol 

everything else but G / Mol are cancelled out.