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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.

PV=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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