Atomic Absorption Spec

[Chemkid]

What happens to the intensity of light transmitted as the concentration of a CuSO₄ solution increases?

Also, in shinny's notes, it says that AAS is qualitative and quantitative, and can use UV light. My teacher said AAs was quantitative only and used only visivle light. Can someone explain this apparent contradiction to me? (lol, I bet shinny's notes are right!)

Thanks in advance! 

[shinny]

What happens to the intensity of light transmitted as the concentration of a CuSO₄ solution increases?

The intensity should decrease as more light will be absorbed by the ions.

Also, in shinny's notes, it says that AAS is qualitative and quantitative

No they don't D:

and can use UV light

Can't remember enough about AAS to answer this. Anyone else know why I wrote that/if it's wrong?

[Chemkid]

lol, sorry about that, thanks =) Could someone explain to me why the intensity of light transmitted decreases though? That would be awesome!

[TrueTears]

lol, sorry about that, thanks =) Could someone explain to me why the intensity of light transmitted decreases though? That would be awesome!

Because the solution "absorbs" the light, hence the name Atomic Absorption Spectroscopy, it measures the absorption of the solution

so the intensity of light transmitted through decreases

[Chemkid]

Thanks Truetears! so when they say "transmitted", they dont mean the colour we see the solution, but the amount of light that passes through. Is that right? 

[TrueTears]

Do you mean transmitted light? If so, then that's the light that is transmitted through, or as you say it, passes through.

[khalil]

On another note, what is the point of chopping pulses of light in AAS?

[TrueTears]

Ok, basically when you shoot the light at the sample will emit that same light.

If you just have a continuous ray of light, then there will be interference due to the emission of light by the sample.

Thus by pulsing the light, it will avoid the interference.

[khalil]

srry i still dont understand!

[TrueTears]

AES (atomic EMISSION spectrum) works by shooting light which have the EXACT energy level required to "push" an electron to a higher energy level which causes it to emit light
AAS works by the fact that if that sample emits that certain amount of energy then it must have RECEIVED exactly the same amount of energy(same as in the same energy it emitted) in order to push it to a higher energy level.

So therefore if you do not shoot pulses of light at that sample, then the light that is emitted will interfere with the light that is absorbed.

By chopping the light into pulses, you avoid these interferences.

[shinny]

To elaborate on what TrueTears has said, basically the fundamental basis of AAS is that metals will absorb light of a particular wavelength, and that the amount transmitted or absorbed, would be proportional to the concentration of that metal in the sample. However, do remember that when these metals absorb this light, they're in an unstable state and will eventually emit this exact same wavelength of light again to reach a stable 'ground' state again. This causes problems for the AAS technique as you're essentially having the light which was previously absorbed being re-emitted and reaching the detector. This would cause the detector to register this light as well, and would cause the detector to think that the amount of light transmitted is greater than it actually is. Hence, the light from the lamp is pulsed, and the detector is designed to only count light which is pulsed to avoid confusing light from the lamp, and light which is re-emitted.

EDIT: TT beat me to it D:

[/0]

Great explanations TT and shinny! Just wondering, is AES part of the course? My class seems to only be covering AAS o_O

[TrueTears]

Great explanation shinny, owns mine

AES is part of the course, it's not that hard, should be able to just remember it easily

[shinny]

I think you just need to understand AES and that's about it. At most, I think it'll just come as a multiple choice question in the exam since there's not really that much to it...

[khalil]

Thank you. Btw, how do u know this stuff? It doesnt explain it in the textbook or any lecture notes that I've read.