AES question (1 Viewer)

[Steven12]

ok. AES measures the range of spectrums given off by a particular elements and determine its nature

but what happens when you have like 3 or 4 different kind a elements in and give off a mixed spectrum of light?

how do you determine the metal ions present then?

And erm. i never really knew how AES work anyway. i understand the part of measuring the spectrum.
But by only measuring a certain spectrum. how do we know the energy required(correspond to the wavelength) for that spectrum to be released fromt the Unknown element?

(say in a spectrometer, it detected violet lights given off by an unknow element? yep its violet alright. lota elements give of violets if you input the right energy. so now what?)
I hope i dont sound simple minded, but please enlighten me

 

[xiao1985]

in AES, i believe a range of spectrum will be detected with regards to the particular element's energy orbitals... so there will be a pattern of spectrum of emission... if you see the particular pattern, you will know the particular element that is present...

it does get alot trickier if you have a mixture of elements... i believe you would have to match the wavelength with corresponding element that emit them... then you can deduce which ever elements are present in the mixture...

sorry if it doesn't make much sense... i am having a terrible cold... my brain is like as if it has lead in it... =(

 

[Xayma]

Even if it is violet it will still be different wavelengths, so you can still find it, and for the actual compositions Im sure there is a way to determine concentrations etc, because the emission spectra is how they determine the composition of stars.

 

[Steven12]

erm

OK. now when an atom gets excited, does it emit only one spectrum of light (say violet) or does it emit one whole range of light?


And also. with AES

do you burn the sample and then measure the spectrums given off, study of the characteristics of the lights given off.

or do you just simply get a light source that emits light with wavelenth that the Element will absorb,and just determine whether the light is absorbed or not.
and then determine the element?

 

[Xayma]

It will emit a few seperate wavelengths of light, which would be part of a colour, or possible infrared. It will absorb the wavelengths of light it emits

 

[CM_Tutor]

AAS - irradiate with monochromatic light (one wavelength), look at intensity directly opposite source, and measure absorption.

AES - irradiate across spectrum of interest (visible, say), look at intensity from 90° from source, measure emission.

In AES, identify elements not by individual lines, but rather by a 'fingerprint' set of characteristic lines. Eg. both sodium and helium emit at 588 nm, but sodium also emits at 285 nm whilst helium does not. All lines of an element should be present before ID is confirmed. Mixtures aren't a problem, as you just get all elements spectra superimposed. Have a look at Conquering Chem, Fig 6.12, p. 219 to see what I mean.

 

[Steven12]

So, you are saying,
with AES, you have multiple test results for a sample of heavy metals.

Irradiate a wide range of spectrums at the sample and then obtain the results.
some are absorbed, some are not. absorbed spectrums are the emission spectra.

compare the results to the charcteristics(emission spectrum) of the element which you think is present in the water, the matched spectrum with a particular element suggest it is present in the water.

Just tick("ohe there, it absorbs 285nm wavelength, must be sodium)(sodium absorbs 588nm as well, does it match?)(ohe yes it does too, yep confirmed)

like that>?

 

[CM_Tutor]

Steven12, the usual question would give the emission spectra of a few metals, and then the spectrum of an unknown, and ask you to identify the metal(s) in the unknown. For the unknown to contain metal X, the unknown must show all the lines in the X emission spectrum.

So, you identify one metal in the unknown, then ignore all the lines due to it, and try and identify the origin of all the lines that are left.

Does this make sense?

 

[Steven12]

yea i think so

you are saying that if we can first identify one metal in the spectrums given(even though some of them may have same emission spectrums for certain color, they must have some color that doesnt match)

after knowing one of the metal, used to unmatched spectrums to identify the rest of the metals. its just logic

 

[04er]

what!? AES!? where did you guys get that from :|

 

[xiao1985]

AES - atomic emmission spectroscopy...

similar principle to AAS, if you excite the electrons around the atom to the next energy level, when it drops back down, it emits EMR of a discrete energy (or frequency)... hence, instead of seeing a specrum of light, u will see discrete emissions at particular frequencies...


edit: AES is not in the syllabus...