You are trying to determine, by experiment, the formula of a gaseous hydrofluoro

Question

You are trying to determine, by experiment, the formula of a gaseous hydrofluorocarbon compound you made to replace chlorofluorocarbons in air conditioners. You have determined the empirical formula is CHF_2, but now you want to know the molecular formula. You therefore do an experiment to determine its molar mass and find that a 0.100 - g sample of the compound exerts a pressure of 69.5 mm Hg in a 261 mL container at 23.1 degree C. What is the molar mass of the compound? What is its molecular formula?

Explanation / Answer

pressure = 69.5 mmHg = 0.09145 atm

volume = 261 mL = 0.261 L

temperature = 23.1 oC = 296.25 K

P V = n R T

0.09145 x 0.261 = n x 0.821 x 296.25

n = 9.81 x 10^-3 mol

moles = mass / molar mass

9.81 x 10^-4 = 0.100 / molar mass

molar mass = 102 g /mol

Emperical formula = CHF2

mass of emperical formula = 51 g/mol

n = 102 / 51 = 2

Molecualr formula = n x emperical formula

                             = 2 x CHF2

Molecualr formula = C2H2F4

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