Question

The density of an unknown gas is found to be 3.44 g/l at standard temperature and pressure (stp). what is the molar mass of this gas? 32 g/mol 48 g/mol 64 g/mol 77 g/mol

Answer 1

To calculate the molar mass of a gas, without knowing density, we would alter the equation:

PV = (mass / molar mass)(RT)

we know density and the units are mass / volume

altering the equation to accommodate density

PV= mass x RT x molar mass.....taking note that mass / volume = density, g/L

P = dRT / molar mass

solving for molar mass:

molar mass = dRT/P

3.44g/L x 0.0821L-atm/mole-K x 273K / 1atm = molar mass = 77.1g/mole