What mass of each gas is present in a 1.15 - l sample of this mixture at 25.0 ∘c?

total pressure = 666/760=0.876 atm

moles gas = 0.876 x 1.10 L / 0.08206 x 298 K=0.0394

moles N2 / 0.0394 = 330 / 666

moles N2 = 0.0195

mass N2 = 0.0195 x 28.0134 g/mol = 0.546 g

moles O2 / 0.0394 = 126/666

moles O2 = 0.00745

mass O2 = 0.00745 x 32 g/mol=0.239 g

moles He / 0.0394 = 210 / 666

moles He = 0.0124

mass He = 0.0124 x 4 g/mol=0.0497 g