More ... Qualitative Analysis
Yoz all,
Hope you are enjoying your hols. I'm sure you have completed your task assigned by Mr Clow Snide right?! If not, you will be banished to his Kingdom (where huh??) when I see you next week... *evil grin*
Anyway, I'm going to start a new discussion about QA.
From our lessons, we have learnt to identify H+, NH4+ and some metal cations based on their reactions with carbonate, zinc, litmus paper, alkalis and lead(II) nitrate. (Can still remember which test is for which ions??!)
If all these tests fail to give us any positive results, then we may conclude that "Group I metal ions may be present". I've told you that the flame test could actually be used to identify the metal ion present.
So here's a link for you to read about flame test:
http://chemistry.about.com/library/weekly/aa110401a.htm
The article states that "the flame test is limited by interference from other brighter colors and by ambiguities where certain different metals cause the same flame color".
Now, my question is: Can we use flame test to positively identify the metal ions? If so how? What is the principle behind this technique?
Let's discuss using the comments function. The one who contributes most to this discussion will get ..........
Picture taken from http://elementy.ru/trefil/36
The picture shows flames of three burning substances, each containing the elements sodium, strontium and boron (from left to right) respectively.
Hope you are enjoying your hols. I'm sure you have completed your task assigned by Mr Clow Snide right?! If not, you will be banished to his Kingdom (where huh??) when I see you next week... *evil grin*
Anyway, I'm going to start a new discussion about QA.
From our lessons, we have learnt to identify H+, NH4+ and some metal cations based on their reactions with carbonate, zinc, litmus paper, alkalis and lead(II) nitrate. (Can still remember which test is for which ions??!)
If all these tests fail to give us any positive results, then we may conclude that "Group I metal ions may be present". I've told you that the flame test could actually be used to identify the metal ion present.
So here's a link for you to read about flame test:
http://chemistry.about.com/library/weekly/aa110401a.htm
The article states that "the flame test is limited by interference from other brighter colors and by ambiguities where certain different metals cause the same flame color".
Now, my question is: Can we use flame test to positively identify the metal ions? If so how? What is the principle behind this technique?
Let's discuss using the comments function. The one who contributes most to this discussion will get ..........
Picture taken from http://elementy.ru/trefil/36
The picture shows flames of three burning substances, each containing the elements sodium, strontium and boron (from left to right) respectively.
posted by Potassium Hydroxide | 8:59 PM
13 Comments:
For brighter colors an optic filter can be used ... like the article mentions to remove the light from sodium
For those of the same color the light can be tested with a spectrometer because elements all have a specific emission spectrum
Very good!
Now, what is an emission spectrum and why do different elements have different emission spectrum?
Anyone has a suggestion?
The emission spectrum is caused when electrons go into a more excited state from being heated then dropping back to a less excited state by emitting energy
Since each element has a different "allowed" energy band level for the electrons there is a different emission spectrum for elements
opps remove the "band" in the last comment
Comments, anyone?
An emission spectrum show the wavelengths of light that an excited atom emit. The wavelengths are determined by how much energy the photon has which is determined by the energy difference of the energy level the excited electron was in and the energy level it dropped to.
Different elements have different emission spectrums because the gaps between energy levels are not [all?] the same.
I dunno?
Why is it only metals can be identified with this spectrum and not non-metals? (At least that is my impression) Does this have anything to do with valence electrons?
Will metal cations give different results from the metal? It shouldn't right... I kind of imagine the cations gaining electrons to become metal atoms or something...
the fact that discrete energy levels exists at all is due to the fact the energy is quantized isit...
isit that different elements have different 'energy levels' or that they have different energy level gaps?..
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/bohr.html
Hmm?
http://chemed.chem.purdue.edu/
genchem/topicreview/bp/ch6/
bohr.html#bvsreal
hmm... how about:
When the electrons in the element are excited, they jump to higher energy levels. As the electrons fall back down, and leave the excited state, energy is re-emitted, the wavelength of which refers to the discrete lines of the emission spectrum. - Wikipedia
Since electrons exist in a set shells ( energy levels) when the electrons are heated, they will have to move onto a higher energy level before falling back. And this energy difference between the energy levels will be different for all elements due to the ENC, number of shells(part of ENC)and number of electrons
I could find anything about why it differs. as in the factors..
but did found website giving emission spectrum for different elements so maybe we can look for some patterns...
http://jersey.uoregon.edu/vlab/
elements/Elements.html
Generally... the small elements and the big elements give the simplest spectrums - least lines..
generally, if you look at some of the spectrums, the lines converge.. get closer together from right to left (longer wavelengths to shorter wavelengths)
i tried looking down groups and across periods but didn't see any obvious patterns...
Other devotees, please contribute?
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