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Testing for Cations: Flame Test (1 Viewer)

Aerials

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Hi everyone. I was wondering if anyone could possibly help me out with a question for a prac-assignment I'm going to have soon. The questions concerns the flame-test for cations (as you may have guessed :rolleyes: ).

"Is the flame colour due to the metal ion or the anion present? Why?"

Am I right to say that this is due to the decomposition of the compound into elements by the flame. And that it is atoms of one of the elements that give the flame its colour. (thats pretty much what I got out of the chemistry book). But is there more I should say about this or is this sufficient to answer a two-mark question?

And also what are the ions present in the compounds Fe(NO3)2 and FeCl3. I would highly appreciate any help or comments. Thanks for your time!
 

TheKing

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Flame test... i little intooxicated right now, but i think its got to do with,
every different element has a different distance between each ring of electrons and the flames provide energy for an electron to move to the next ring. each element requireds a different amount of energy to move on(energy is the form of light at different wave lengths) and it momentarily absorbs this energy and then releases it as it moves back to its normal place.

dunno if i've answered your question, that applies if your looking through a spectrometer i think, well at least thats why they give different clours... i think

should really get someone else to answer this one

sorry to waste your time

goodnight
 

TheKing

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sorry forgot to add that, an atom will only absorb a certain wavelength and therefore release a certain wavelength, and giving a specific colour....
hopefully i'm correct
please tell me if i'm not
 

xiao1985

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in metals molecular orbitals, the electrons occupy a certain energy level... when energy has being added, they jump to a higher energy level... since the energy level is discrete, also, due to the different interactions between the nucelous and teh elctrons, the energy difference in orbitals are different... when elctrons drop down, they emit EMR... due to the different energy change (because of the interaction between nuclous and number of electrons there is), the EMR emitted would be a different energy ( different wavelength) hence giving off different color...
 

Aerials

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Please excuse my ignorance, but I still don't see how the response justifies wether the colour is dependant on the metal ion rather than the anion. I know this is probably very easy but I just can't grasp the concept. Can't the anion emit the colour? Why or why not? Thanks for putting your time into responding to the post by the way :) as Homer would say "could you dumb it down a shade?"
 

spice girl

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no you're not ignorant; it hasn't been answered yet

anions also absorb / emit energy. the difference is that the cations emit energies corresponding to the visible-light part of the EMR spectrum, whilst anions emit energies corresponding to higher (perhaps UV) part of the spectrum and thus their different flame colour cannot be seen.
 
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And also, if you use different metal cations with the same anion, like chloride, you can see the difference is that the metal, and not the non-metal, is producing the colour.
 

Aerials

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Excellent! Thankyou both for responding. I can completely understand what's going on now! :) Thanks again
 

Aerials

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And also could you tell me what are the ions present in the compounds Fe(NO3)2 and FeCl3? And how I can deduce the ions in different compounds for future reference? This should be like preliminary stuff... I feel so stupid :(
 

xiao1985

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Cl has a -1 charge (usually) hence in Fe(Cl)3, you Fe 3+ cation...... NO3 has a -1 charge as well, hence in Fe (NO3)2, you have Fe2+ cation

edit: apologies to theKing and aerials... =p i wasn't concentrating when i was posting the first post ... hence causing all the trouble =(
 
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Fe(NO3)2 has Fe2+ (Iron(II) ions) and 2 NO3- (nitrate ions). FeCl3 would have Fe3+ (Iron(III) ions) and 3 Cl- (chloride ions).

Just remember that Cl- has a valency pf -1 so if it is Cl3, then there is a -3 charge which needs to be balanced by +3, so the iron in that has to have a valency of +3 making it Iron(III).

Same with NO3- which has a valency of -1. So if its (NO3)2, it has a valency of -2 which needs to be balanced by +2 so that iron has a valency of +2 making it Iron(II).

Ferrous is iron(II) or Fe(2+)
Ferric is iron(III) or Fe(3+)
 

Aerials

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haha I love you guys. Im actually learning something! Thanks so much! If theres anything I can do (I highly doubt it), please don't hesitate to ask.
 

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