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Author Question: Possible molecular formula for a gas and placed into a container? (Read 1230 times)

federox

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on: Oct 4, 2013
What is a possible molecular formula for a 4.35g sample of gas that has a density of 1.45g/L when placed in a container at 21.0C and 1.25 atm?

Note: R = 0.0821 L atm mol^-1 K^-1

please show work! thanks so much!


dalyningkenk

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Reply #1 on: Oct 4, 2013
Given the Ideal Gas Law
PV = nRT
n = mass of gas (m) / molecular mass (M):
PV = (m/M)RT
Density is mass per volume, so, rearranging,
PM = (m/V)RT, or
PM = dRT, where d = density.
M = dRT/P; substituting,
M = (4.35g ) (R = 0.0821 L atm mol^-1 K^-1) (294.15 K) / (1.25 atm)
M = 84 g/mole
The permanent gas closest to this molecular mass is Krypton (Kr), MW = 83.9 g/mole.


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