# Calculate the molar weight of Freon-II, if 8.29 liters of its vapor at 200 °C and 700 mm Hg has a mass of 30.5 g?

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this problem can be solved using the ideal gas equation.

`PV = nRT`

Where:

P = pressure in atm = 700/760 = 0.9211atm

V = volume = 8.29L

R = gas constant, 0.08206 atm-L/mol-K

T = temperature in Kelvin = 200 + 273 = 473

n = numbers of moles = Mass/molar mass

mass of the compound = 30.5

we can rewrite the equation above as

`PV = (Mass)/(Molar mass) * RT`

by arranging this we can solve for Molar mass

`Molar mass = Mass (RT)/(PV)`

`Molar mass = 30.5 * (0.08206*473)/(0.9211*8.29)`

**Molar mass = 155 g/mole**