Question

After a 2.60 L container weighing 500.00 g is filled with butane gas it weighs 506.31 g. The gas was stored at a temperature of 20.0°C and a pressure of 102 kPa. Calculate the molar mass of butane gas.

Answer 1

Recall the ideal gas equation: PV=nRT.

So you have everything except n(# of moles). BUT remember that you can relate n with MM(molar mass) like this ---> mass/MM = n because the units cancel:
grams =mass grams X mole
------- ====> --------
(grams/mole) =molar mass grams

So the NEW eqtn is:

PV=mRT which you can turn into MM=mRT
--- ======> _____
MM PV

Remember to use the right R value though!