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Homework Help: Density of a gas

  1. Nov 7, 2009 #1
    1. The problem statement, all variables and given/known data
    Assuming ideal gas behaviour, what would be the density of gaseous ethane (C2H6) at 30. °C and 771 mmHg?

    2. Relevant equations

    Ideal gas laws.
    I'm using:
    Density = MP/RT (M is g/mol)

    3. The attempt at a solution

    This is one of the questions due online by Sunday night. They're marked by the computer, and we get only a limited number of tries. Anyway, this is my answer and how I arrived at it:

    -- M = 2*16+6*1.008 = 38.048 g/mol
    -- T = 30 + 273.15 = 303.15 K
    -- P = 771/760 = 1.014 atm
    -- R = 0.0821 atm*L/mol*K
    => d = MP/RT = (38.048*1.014)/(0.0821*303.15) = 38.43/24.88 = 1.54 g/L

    I've tried rounding to 2 digits, to 3 digits... every possible combination. I've gone over the numbers a bazillion times and it keep telling me I'm wrong, and I have 1 try left. What am I doing wrong?
  2. jcsd
  3. Nov 7, 2009 #2
    zomg. neevermind. C = 16 ?? glah :yuck::yuck::yuck:. this is the sort of stupid mistake that ends up costing me the A.

    no soup for me.
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