You need to use the following formula: d = [tex] \frac{M*P}{R*T} [/tex]
d is the density
M = ethane's molar mass = 30.1 g/mol
P = pressure = 1.31 atm
R = universal gas constant = 0.08206 L x atm/mol x K
T = temperature = 31º C but needs to be converted to kelvin, so 304.15º K
d = [tex] \frac{30,1 * 1,31}{0,08206*304.15} [/tex]
d= 1.58 gram/L
