Question

What is the molar mass of a gas if 1.30g of the gas has a volume of 245mL at STP?

Answer 1

start with PV=nRT. Solve for n.
n = PV/(RT)
stp means 273.15 K and 1 atm. (Must use absolute temperature). R = gas constant.
n= (1 atm * .245 )/(273.15 * .08206) = 0.0109303 mols

Answer 2

molar mass is grams/mole.
1.3g / 0.0109303 mol = 118.9 g/mol