another gas question?

Question

In a mixture of H2 and CH4 gases, the partial pressure of H2 is 0.120 atm. The total pressure is 0.415 atm. The temperature is 30.0oC. If the total volume of the gas mixture is 394 mL, what is the mass of CH4 in grams?

Answer 1

Somebody else posted a virtually identical question just a few minutes ago. Here's how you do these: use the ideal gas law to get moles then calculate grams.

Getting things in the proper units:

30.0 C = 273 + 30.0 = 303K

PP of CH4 = 0.415 - 0.120 = 0.295atm

n = PV/RT =

(0.295atm x 0.394L)/(0.08206Latm/molK x 303K) =

0.00467mole

To get grams: multiply by grams/mole for CH4:

0.00467mole x 16g/mol = 0.0747g