Question

3L of a gas weighs 2g. What is the molecular mass? (Note: STP)
Not sure where he went with the 2nd step, help?:)
http://ca.answers.yahoo.com/question/index?qid=20090831083358AAfHiBq

Answer 1

\[PV=nRT\]\[PV=\frac{m}{MM}RT\]\[MM=\frac{mRT}{PV}\]\[MM=\frac{(2g)(0.08206\frac{L*atm}{K*mol})(273.15K)}{(0.986atm)(3L)}\]\[MM=15.1553\frac{g}{mol}\]We're only technically able to report back 1 significant figure, but if I were you I'd report the answer as something like...\[15.2\frac{g}{mol}\]

Answer 2

The question and answer you posted aren't really related to the way you do this problem, by the way.