Chemistry Question?

Question

I'm having a real hard time with a Chemistry homework question:

A sample 13.03 g of gas was collected and found to have a volume of 6.742 L at 46.6 degrees Celsius and 723.3 torr. What is the molar mass of the gas?

I converted 723.3 torr to 0.9517 atm, and 46.6 celsius to 319.75 K. I then worked it like this using the PV=nRT equation:
(0.9517 atm)(6.742 L) / (0.0821)(319.75 K) = 0.244 mol
(0.244 mol)(13.03 g/mol) = 3.18 g

However, my program says that 3.18 is not the correct answer. What am I doing wrong?
Any help is greatly appreciated!!

Answer 1

Dude; you almost had it, you multiplied at the end instead of dividing!

Set it up like this:

PV = nRT

PV/RT = n

[0.9517atm x 6.742L]/[0.08206Latm/mol K x 319.75K] = n

n = 0.245mole

13.03g/0.245mole = 53.18 g/mol

Answer 2

Well, PV=nRT is inherently flawed, as it applies only to ideal gasses, of which there are none - try the Henderson-Hasselbach equation; that'll give you a more precise answer.
If that's not it, your program is wrong.