A 1.20-L container contains 1.10 g of unknown gas at STP.What is the molecular weight of the unknown gas?

Answer 1

hmmmm. At STP a mole of any gas occupies 22.4 liters, so

1.20/?moles=22.4/1mole
solve for ? moles, then
?moles=1.10g/molmass solve for molmass.

Answer 2

1.10g/mole

Answer 3

1.20 L*1 mole/22.4 L= 0.05357 moles
L units cx out.
Then use your given mass of
1.10 g/0.05357 moles=20.5 g/mole