Chemistry problem involving gas laws

AI Thread Summary
To determine the percent chlorine by mass in the unknown chlorofluorocarbon, the user applied the ideal gas law (PV=nRT) to find the number of moles of chlorine gas produced, resulting in 0.02245 mol. This led to a calculated molar mass of 124.69 g/mol for the compound. The user attempted to set up an equation to find the mass percent of chlorine but initially arrived at an incorrect value of 21.09. Clarification was provided on how to calculate the grams of chlorine from the moles obtained. The discussion concluded with the user expressing understanding of the solution process.
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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?
 
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How many grams of chlorine are in 0.02245 mol of Cl2?

Compare that to 2.80 g.
 
but we don't know how many grams we have of chlorine...?
 
You know how many moles and how many grams/mole for chlorine. Use that.
 
okay thank you i got it!
 
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