chemistry home work questions?

Question

1. A tank contains both Nitrogen and hydrogen gas. If the partial pressure are 190 mmHg and 303 mmHg respectively, what is the mole fraction of nitrogen?

2. if 4.0 grams of hydrogen, 6.02 * 10 ^ 22 atoms of helium and 4.48 L of argon, measures at stp, are placed in a 2.0 Liter flask at 27 degree celcius, what is the final pressure.

Answer 1

1. Ideal gas is very good model at such low pressure. Wth this model, the mole fraction is the same as pressure fraction:
So the answer is: 190/(190+303) = 38.5%.

2. 4.0 g of H2: 2.0 moles.
6.02*10^22 atoms of helium: 0.1 moles.
4.48L Ar, measures at stp: 4.48/(0.08206*273) = 0.2 moles
Total 2.3 moles. The final pressure is:
P = nRT/V = 2.3*0.08206*300/2.0 = 28 (atm)