For this problem, we assume that ethane gas is an ideal gas so we can use the ideal gas equation which is expressed as:
PV = nRT
We first find the number of moles using the above equation.
n = PV / RT
n = (1.6 atm) (12.7 L) / (0.08206 L atm/mol K) (24 + 273.15 K)
n = 0.83 mol C2H6
M = 0.83 mol C2H6 ( 30.08 g / 1 mol ) = 2.97 g C2H6