A 2.90 -g sample of an unknown chlorofluorocarbon is decomposed and produces 572 mL of chlorine gas at a pressure of 754 mm Hg and a temperature of 298 K.

What is the percent chlorine (by mass) in the unknown chlorofluorocarbon?

We’re being asked to calculate the percent chlorine (by mass) in the unknown chlorofluorocarbon.

**Decomposition reaction: CHFCl _{(g)}**

*We’re going to **calculate the percent chlorine (by mass) in the unknown chlorofluorocarbon using the following steps.*

*Step 1**. Calculate the moles of Cl _{2} produced using the ideal gas equation.*

$\overline{){\mathbf{PV}}{\mathbf{=}}{\mathbf{nRT}}}$

P = pressure, atm

V = volume, L

n = moles, mol

R = gas constant = 0.08206 (L·atm)/(mol·K)

T = temperature, K

**Step 2**. Calculate the mass of Cl_{2} produced using its molar mass.

**Step 3**. Calculate the percent chlorine (by mass) in the unknown chlorofluorocarbon.