What is the mass of 7.0 L of hydrogen gas?

1 Answer
Dec 23, 2014

In order to determine the mass of any gas you need the set of paramaters that describe that gas - pressure, volume, temperature and/or moles. If values are given for these paramaters, you could use the ideal gas law, PV=nRT, to go about solving for mass.

If you are dealing with STP conditions, which I assume is the case here, remember that in this case pressure is equal to 1.00 atm and temperature is equal to 273.15K. So,

PV=nRTn=PVRT=1.00atm7.0L0.082atmLmolK273.15K=0.31

Since we know hydrogen's molar mass (2.0gmol), we can determine the mass

mH2=nmolar.mass=0.31moles2.0gmol=0.62 g

If indeed you are dealing with STP, remember that, under these conditions, 1 mole of any ideal gas occupies 22.4L. So,

n=VVmolar=7.0L22.4L=0.31 moles

And, once again, m=0.312.0=0.62g