Thread: Identification

I'm very curious as to how chemists determine the specific structures of chemical compounds. For an example, if I set a beaker of a pure colorless solution in front of you and gave you absolutely no information on it, how would you determine what exactly it was, and its structure, # of what specific atoms, etc.? Please be very specific.

Well, if it's all liquid you could use fractional distillation to determine the boiling points of the mixtures (which gives you some good info of what they are), and if there are any salts they'll remain at the bottom that you can then test.

You could also get a lot of information by taking pH along the way.

You could also take samples and simply use different types of spectroscopy to find out what exactly those compounds are, and their structures.

There are really about a million ways to do it.

I don't feel like being very specific because this is a very vague hypothetical situation and I don't feel like posting an analytical chemistry textbook on this forum.

A chemist would most likely put the colorless solution into gas chromatography/mass spectrometer machine, which would tell how many different chemicals are in the solution, the relative concentrations of the different chemicals, and the exact masses of each type of molecule in the beaker. GC/MS machines are by far the most common way that chemists determine what's in unknown substances.

If the material turned out to be a very complex substance that couldn't be easily identified by GC/MS, there are other techniques like NMR and IR spectroscopy that would be used, but those are fairly complicated.

Actually NMR and IR are each insanely easy. NMR machines are relatively expensive though.

Of course you'd use chromatography to seperate, I noticed that was absent from my first post.

There are literally is a million ways to do it.

Originally Posted by silkworm

Actually NMR and IR are each insanely easy. NMR machines are relatively expensive though.

I meant dificult to explain - no one wants to try to explain how NMR works in a forum post.

Originally Posted by Scifor Refugee

Originally Posted by silkworm

Actually NMR and IR are each insanely easy. NMR machines are relatively expensive though.

I meant dificult to explain - no one wants to try to explain how NMR works in a forum post.

Oh, yeah. I certainly agree with you on that.

Chemboy, just study chromatography and spectroscopy. There are many different methods of each that have different advantages and disadvantages. And then go study crystallography. That should get you a pretty good idea.

can you please tell me what NMR stands for so maybe I can do some reading on my own about it? and thank you for your answers. <oh, and if you were wondering, this really isn't hw or anything, i'm just interested in it>

never mind, i just got it. good ol' wikipedia...