8. A chemist vaporized a liquid compound and determined its density. If the density of the vapor at 90 ºC and 753 mmHg is 1.585 g/L, what is the molecular weight of the compound?

Answer 1

If you modify the formula for ideal gas (PV = nRT) a little, you'll get an expression for the density of gas:
ρ = P*MM / RT
where
ρ = density (g/L)
P = pressure (atm)
MM = molar mass (g/mol)
R = universal gas constant = 0.0821 L-atm/mol-K
T = absolute temperature (K)

Solving for MM, we'll have
MM = ρRT / P
Now substitute the given values but don't forget to convert them first to the appropriate units.

hope this helps~ `u`
(I apologize is someone already posted an answer/solution before me. My internet is really slow and I can't seem to post a comment right away.)