Homework Problems dealing with Pressures?

Question

Hey guys. I am having trouble with number one. I am lost on it. On number 2, I said No and 2L that right? Thanks

1) A gas of unknown molecular mass was allowed to effuse through a small opening under constant pressure conditions. It required 113 s for 1.0 L of the gas to effuse. Under identical experimental conditions it required 31 s for 1.0 L of O2 gas to effuse. Calculate the molar mass of the unknown gas. (Remember that the faster the rate of effusion, the shorter the time required for effusion of 1.0 L; that is, rate and time are inversely proportional.)

2)Suppose you are given two flasks at the same temperature, one of volume 2 L and the other of volume 3 L. In the 2-L flask the gas pressure is X atm, and the mass of gas in the flask is 4.8 g. In the 3-L flask the gas pressure is 0.1X, and the mass of gas is 0.36 g.
(a) Do the two gases have the same molar mass?
Yes
No
(b) If not, which contains the gas of higher molar mass?
Gas in 2-L
Gas in 3-L

Answer 1

1) Graham's law of effusion says that the rate of effusion is inversely proportional to the square root of the molecular mass. Hence the effusion time would be directly proportional to the square root of the molecular mass. Thus the required molar mass is:
(32g/mol)*(113/31)^2 = 425g/mol
I do not believe there is such a gas.

2) You are right.