Chemistry problem involving gas laws

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SUMMARY

The discussion centers on calculating the percent chlorine by mass in an unknown chlorofluorocarbon after decomposing a 2.80g sample that produces 552mL of chlorine gas at 756 mmHg and 298K. Using the ideal gas law (PV=nRT), the number of moles of chlorine gas was determined to be 0.02245 mol. The molar mass of the compound was calculated to be 124.69 g/mol, but an algebraic setup for mass percent yielded an incorrect result of 21.09%. The correct approach involves determining the mass of chlorine in the produced moles and comparing it to the total mass of the compound.

PREREQUISITES
  • Understanding of the Ideal Gas Law (PV=nRT)
  • Knowledge of molar mass calculations
  • Familiarity with algebraic equations for mass percent
  • Basic concepts of chlorofluorocarbon chemistry
NEXT STEPS
  • Calculate the mass of chlorine in 0.02245 mol of Cl2 using its molar mass (35.45 g/mol).
  • Review the derivation of the mass percent formula for compounds.
  • Explore the properties and applications of chlorofluorocarbons in chemistry.
  • Investigate common mistakes in stoichiometric calculations involving gas laws.
USEFUL FOR

Chemistry students, educators, and professionals involved in chemical analysis and stoichiometry, particularly those working with gas laws and chlorofluorocarbons.

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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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