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Gas Stoichiometry

  1. Aug 6, 2007 #1
    1. The problem statement, all variables and given/known data
    A sealed 1.00 L vessel contains 0.3475 g of argon gas and 6.766 g of an unknown gas at 350 K. If the total pressure of the gas mixture is 2.56 atm, and the unknown gas has an empirical formula of CH2, what is the molecular formula of the unknown gas?

    2. Relevant equations
    I get stuck about halfway. I find the mole fraction of Ar but I'm not sure if its right, if someone could help me on how to finish the problem please? How do I find the molar mass of the unknown?

    3. The attempt at a solution

    I used the mass of the Argon Gas to find the number of moles (0.00869 mols), then ideal gas law to find the pressure of argon gas (2.49 atm). Then using mole fractions, P1=X1*Ptot,I get X for Argon as 0.097, or 9.7% Argon Gas.

    Is CH2 = 90.3% then, so X = 0.903? What do I do afterwards?
  2. jcsd
  3. Aug 6, 2007 #2


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    You know the temperature, volume and pressure of the vessel. Assume that the mixture of gases acts in an ideal fashion (PV=nRT). From this you will know the total number of moles of the binary mixture. You already precisely know the number of moles of one of the components.
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