At STP, 13.0 L of methane has a mass of 9.18 g.
You will need the molar volume of a gas at STP
At STP of
You will need to determine the moles of methane by dividing the volume in liters of methane by its molar volume at STP.
In order to determine the mass of 13 L of methane at STP, you will need to multiply the moles of methane times its molar mass.
Molar mass of