# Solution: 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?

###### Problem

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?

###### Solution

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

Decomposition reaction:             CHFCl (g) ⟶Cl2(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 Cl2 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 Cl2 produced using its molar mass.

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

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