Why use a spectrometre?

[raid517]

Can someone please explain why you would use a spectrometer rather than a simple flame test to identify the atoms in an unknown mixture? I'm guessing that the spectrometre would divide the spectra into a much more specific pattern, so that you could identify the individual elements in the unknown mixure, wheras the flame would only give you a mix of colours, thus giving the flame a single coulour consisting of all of these different colours. So the flame test would make guessing the elements of the unknown mixture impossible. But I'm not sure if this is the best answer I can give to this question? Maybe they are looking for something more specific, or am I just overcomplicating things?

[hypervalent_iodine]

Because flame tests are unreliable and you can make quantitative measurements with spectrometry and spectroscopy that you can't with with a flame test.

[John Cuthber]

Only a handful of elements give a result with a flame test and you can't tell, for example, boron from copper or barium because they all give a green flame. A spectrometer will give much better specificity.

Also, if there's any sodium present (and there generally is) most of the colour you see is the yellow from that.

[raid517]

Thanks guys. I was along the right lines it seems, but you made it much clearer. Thanks!

 

I don't get the part where you say:

 

Also, if there's any sodium present (and there generally is) most of the colour you see is the yellow from that.

 

There clearly isn't sodium in every sample of an unknown mixture you might be given. So are you simply saying that if sodium is present in a flame test, the strongest constituent of the colour produced in the test would be yellow? Wouldn't this depend how much sodium was present? Clearly if there was very little, then the colouration of the flame test by the presence of sodium would be minimal also?

[John Cuthber]

The flame test for sodium is very sensitive, sodium atoms are really good at giving out yellow light. Also the eye is very sensitive to yellow light so if there's more than the tiniest trace of sodium present you get a yellow flame.

You may have heard the suggestion that most dust round the house etc is dead skin cells. Those cells are covered in sweat which is salty.

Sodium gets everywhere.