# Chemistry problem involving gas laws

1. Oct 8, 2008

### 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/v

Ok, 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?

Last edited: Oct 8, 2008
2. Oct 8, 2008

### Redbelly98

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

Compare that to 2.80 g.

3. Oct 8, 2008

### MellowOne

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

4. Oct 8, 2008

### Redbelly98

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

5. Oct 8, 2008

### MellowOne

okay thank you i got it!