Chemistry Help Please!?

Question

If anyone could help me figure these out I would greatly appreciate it. I have a test tomorrow and these are the only 2 I can't figure out from my review sheet.

An unknown gas occupies a volume of 1.250 L at 26oC and 705 torr. If the sample has a mass of 2.37 g, what is the molar mass of the gas?
(R = 0.0821 L.atm/mol.K)

AND

How many moles of helium gas occupy a volume of 58.7 L at -13.0oC and 1.17 atmospheres of pressure?


BEST ANSWER TO FIRST CORRECT!!!

Answer 1

Ust the ideal gas equation

PV=nRT

P is 705 torr, but you need to convert to atm, so divide by 760
V is 1.250 L, use as is
R = 0.0821
T is 26 0C. Convert to K by adding 273

Now solve for n = moles

2.37 divided by the moles gives you the molar mass

Same for the 2nd problem. Use the same equation and convert your data as necessary to Kelvin

Answer 2

in this exercise you have always to use the eq PV=nRT than u remember that n=g/MW of the gas an u can solve anything