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Homework Help: Finding density

  1. Feb 26, 2007 #1
    1. The problem statement, all variables and given/known data

    OK, the problem says to find the molecular weight of NH3.

    It is 17.03g/mol.

    Next, you are supposed to find the density(in Kg/m^3) for the NH3.

    I'm not sure how you do this part. I don't know if I have to convert or what.

    I know the actual density is 0.771 kg/m^3.

    2. Relevant equations

    D=M/V

    3. The attempt at a solution
     
  2. jcsd
  3. Feb 26, 2007 #2

    hage567

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    It's a gas, you can probably treat it with the properties of an ideal gas. Like so many mols of an ideal gas at STP has a certain volume....etc. Think ideal gas law.

    Does that help?
     
  4. Feb 26, 2007 #3
    Well kinda I guess.

    I know my chemistry(a little)....but I'm just confused(or thinking too much).

    I know that at STP....volume is 22.4 L

    Temp is 273.15K
    Pressure is 1 atm
    n is usually 1 mole

    So how does that relate to density though....do i just divide my mass by the 22.4?(I can't see the units working out)
     
  5. Feb 26, 2007 #4

    hage567

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    Small correction: at STP, the volume of an ideal gas is 22.4 L/mol. Liters are a way of expressing volume, right? So convert that to m^3. You already figured out the molecular mass per mol. Just look at the units (make sure everything is consistent).
     
  6. Feb 26, 2007 #5
    ok......got that figured out.....thanks for your help. Came out to be .760kg/m^3.
     
  7. Feb 26, 2007 #6

    hage567

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    Yeah, the 22.4 L/mol isn't exactly the same for all gases, so depending on where you got the accepted value it might vary a bit.
     
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