J.R. S. answered 04/25/19
Ph.D. University Professor with 10+ years Tutoring Experience
PV = nRT
n = PV/RT = (1atm)(1 L)/(0.0821)(273) = 0.0446 moles O2 at STP
This is also arrived at from the density of 1.43 g/L. 1.43 g x 1 mol/32 g = 0.0446 mol/L0.
P1V1/T1n1 = P2V2/T2n2
n2 = P2V2T1n1/P1V1T2 = (0.988)(0.5)(273)(0.0446)/(1)(1)(294.8)
n2 = 0.0204 moles
0.0204 moles O2 x 32 g/mole = 0.653 g