Ideal gas equation: pV = nRT
Transform it to show density:
pV = [mass/Molar mass] RT
mass/V = (p*molar mass) /(RT)
density = mass / V
density = p*molar mass / (RT)
Now susbtitute the data
p = 1521 mmHg * 1 atm / 760 mmHg = 2.0 atm
T = 25 °C + 273.15 = 298.15 k
molar mass of He = 4.0 g/mol
R = universal gas constant = 0.082 atm*L / mol*k
density =2.0 atm*4.0 g/mol / (0.082 atm*L / mol*k *298.15k)
density = 0.327 g/L
