Question

calculate the molar weight of Freon-II, of 8.29 liters of its vapor at 200 degrees celcius and 790 mm Hg has a mass of 30.5 g.

Answer 1

First note the correct spelling of celsius.

Calculate n = number of mols from PV = nRT. Then n = grams/molar mass. You have n and grams, solve for molar mass. Don't forget to convert mm Hg to atm and T to kelvin.