What is the mass of 7.0 L of hydrogen gas?
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,
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,
Since we know hydrogen's molar mass (
If indeed you are dealing with STP, remember that, under these conditions, 1 mole of any ideal gas occupies
And, once again,