# Can chemicals be identified by their molar mass?

Wouldn't it be possible to identify a chemical by measuring its molar mass? How much accuracy does the measured molar mass need to be to guess what chemical it could be?

EDIT: @ortho makes an important point about isomers, but organic chemistry is much harder ;). Let's just focus on inorganic chemistry (though there are still isomers, usually there aren't).

• To some extent it is, for example you can look up high-resolution mass spectrometry. chemguide.co.uk/analysis/masspec/mplus.html However if you only have the molar mass there's no way you can differentiate between isomers (e.g. n-butane and isobutane) – orthocresol Oct 18 '15 at 21:50
• It’s not like there be no isomers in inorganic chemistry, see cis-diammindichloridoplatinum and trans-diammindichloridoplatinum. – Jan Oct 18 '15 at 22:01
• @Jan i know, but usually there are no isomers, while organic chem is much different.. – TanMath Oct 18 '15 at 22:02
• Sorry, wrong... – Jan Oct 18 '15 at 22:02
• CO and N2 has same molar mass. There is a bunch of other examples as well. – permeakra Oct 18 '15 at 22:33

For inorganic chemicals in general the problem is really one of specificity. So I want to work with a chemical sample between 1 gram and 20 grams and I have an analysis good to 1%. That only yields about 300 statistically significantly different numbers $1.01^{300} = 20$. So for various inorganic salts this wouldn't work too well.