Amixture of helium and neon gases has a density of 0.1562 g/l at 40.2°c and 296 torr. what is the mole fraction of neon in this mixture?

You are given the density of helium and neon gas mixture which is 0.1562 grams per liters at 40.2degC and 296 torr. You are required to find the mole fraction of neon in this mmixture.

c = dRT/P

c = (0.1562g/L)(0.08206 L-atm/mol-K)(40.2+273)K/296torr(1atm/760torr)

c = 10.31 g/mol

since helium is 4 g/mol

mole fraction of neon = (10.31 - 4) / 10.31 = 0.612