## Lukecrayonz 4 years ago 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

1. anonymous

$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...$15.2\frac{g}{mol}$

2. anonymous

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