Once again I can’t figure this out, please help (tenth grade chemistry)

Question

9B. A vessel with a volume of 10.0L contains 2.80 g of nitrogen gas (N2) , 0.403 g of hydrogen gas(H2), and 79.9 g of argon gas (Ar). At 250C, what is the pressure of the HYDROGEN GAS? *

Answer 1

When working with gases and the gas laws, you always want to use MOLES, not grams. So, first thing is we need to convert mass of gas to moles of gas.

moles N₂ = 2.80 g x 1 mol/28 g = 0.1 moles N₂

moles H₂ = 0.403 g x 1 mol/2 g = 0.2015 moles H₂

moles Ar = 79.9 g x 1 mol/39.95 g = 2.00 moles Ar

Since the questions asks only for the pressure of the hydrogen gas, we can simply plug the moles of H2(g) into the Ideal Gas Law equation and solve for pressure. We didn't need to find moles of the other gases. But if you want the total pressure of the system, you could add all moles together, plug that into the equation and solve for P.

PV = nRT

P = pressure = ?

V = volume = 10.0 L

n = moles of H₂(g) = 0.2015

R = gas constant = 0.0821 L-atm/K-mol

T = temperature in K = 25ºC + 273 = 298K (I believe you meant 25 and not 250 C)

Solving for P (pressure) we obtain:

P = nRT/V = (0.2015 mol)(0.0821 Latm/Kmol)(298K) / 10.0 L

P = 0.493 atmospheres = pressure of H₂(g)