mass = 20.48 g
moles=0.1895
Further explanation
In general, the gas equation can be written
Pv=nRT
where
P = pressure, atm
V = volume, liter
n = number of moles
R = gas constant = 0.08205 L.atm / mol K
T = temperature, Kelvin
P=0.23 atm
V=20 L
T=23+273=296 K

mass SF₄ (MW=108,07 g/mol) :
