Chemistry problem involving gas laws

[MellowOne]

A 2.80g sample of an unknown chlorofluorocarbon is decomposed and produces 552mL of chlorine gas at a pressure of 756 mmHg and a temperature of 298K.
What is the percent chlorine (by mass) in the unknown chlorofluorocarbon? PV= nRT
D= m/vOk, so for this problem I tried using the PV=nRT (756*.552=n*62.364*298) equation to solve for n and I got 0.02245 mol. And from that, I figured the molar mass was 124.69 g/mol (having used the mass of 2.80 to derive this answer). And then I tried to set up an algebraic equation with variables to solve for the mass percent. I used the equation (1-x)(31.008) + 35.45x = 124.69. The (1-x) represents the Carbon and Fluorine components of the compound, and the 31.008 is their combined molar mass. The 35.45 is the molar mass of Clorine, and by solving this equation i got 21.09, but this was incorrect. So what should i do?

 

[Redbelly98]

How many grams of chlorine are in 0.02245 mol of Cl₂?

Compare that to 2.80 g.

 

[MellowOne]

but we don't know how many grams we have of chlorine...?

 

[Redbelly98]

You know how many moles and how many grams/mole for chlorine. Use that.

 

[MellowOne]

okay thank you i got it!