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Homework Help: Molar Mass of unknown gas

  1. Jun 24, 2007 #1
    1. A sample bulb contained 0.712 g H2 (g) at a certain temperature and pressure. Under the same conditions of temperature and pressure, the bulb can hold 13.0 g of an unknown gas. What is the molar mass of the unknown gas?

    Obtaining H2 volume from the ideal gas law (assuming STP) and then using that volume to obtain the unknown gas density (with STP) is the correct way to obtain the molar mass?

    I would appreciate some help

    Thank you.
  2. jcsd
  3. Jun 25, 2007 #2


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    Assume the gas follows the ideal gas law. For the hydrogen example you know the pressure/temperature and the number of moles. From that you can calculate the volume of the vessel. Use this solution (same pressure, temperature and volume) to determine the number of moles of the unknown gas. From that you can calculate the molecular weight of the unknown gas.
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