At NTP, what is the mass of #"22.4 L"# of nitrogen gas?

1 Answer
Aug 11, 2017

Well, I can set things up for you to calculate the mass... but weight is in newtons, #"N"#, or #"kg"cdot"m/s"^2#... and you have to decide what the chemical formula of nitrogen is... you have a #50%# chance of guessing it right!


Normal Temperature and Pressure, NTP, is apparently #20^@ "C"# and #"1 atm"#. This should not be confused with STP, which is at #0^@ "C"#, not #20^@ "C"#, and not #25^@ "C"#.

The "mass" version of the ideal gas law can be derived.

#PV = nRT#

#n = (PV)/(RT)#

To get the units from #"mols"# to #"g"#, simply multiply by the molar mass #M# in #"g/mol"#.

#nM -= m = (PVM)/(RT)#

In this case, we have:

  • #P#, pressure, in #"atm"#, of the ideal gas within the container.
  • #V#, volume, in #"L"#, of the ideal gas.
  • #M#, molar mass, in #"g/mol"#, of the ideal gas.
  • #R = "0.082057 L"cdot"atm/mol"cdot"K"#, the universal gas constant.
  • #T#, temperature, in #"K"#, within the container filled with ideal gas.

In case you couldn't tell, we're assuming ideal gases... So, the mass is:

#color(red)(m) = (cancel"1 atm" cdot 22.4 cancel"L" cdot M" g/"cancel"mol")/(0.082057 cancel"L"cdotcancel"atm""/"cancel"mol"cdotcancel"K" cdot (20 + 273.15 cancel"K"))#

#= color(red)(???)#

Now, it's up to you to decide what the molar mass is.

What is the molar mass of "nitrogen"? Is it #"14.007 g/mol"#, or #"28.014 g/mol"#? Why would you have to choose? (It matters!)