1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


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


    User Avatar
    Homework Helper

    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


    User Avatar
    Homework Helper

    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


    User Avatar
    Homework Helper

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook