Chem... random questions (1 Viewer)

[Aerlinn]

-Something I want to make clear: Says in my notes that flame tests are suitable for only a few metal cations... doesn't it mean metal atoms 'cause those are the ones excited?

-Is electrophoresis an example of chromatography? It seems very different... and plus, I'm not aware that it has a mobile phase... unless you count your fragments that are separating as being the mobile phase...
-Is it true that different numbers of protons/elections make energy levels of an element unique?
ie. jumps between levels vary in size, each shell a different energy, eg. 1st shell of one element with more energy than 1st shell of another element...?

-Are there any other types of AES apart from flame tests?

-With titrations, what does a sharp end point mean, in terms of interpreting a graph?

-How does emission spectroscopy allow a great number of metals to be identified? I was under impression that AES can only identify some metals... unless the 'emission spectroscopy' here refers to 'emission spectra'?

:wave:

 

[xiao1985]

a) cations really... because in a salt, you dont' have metal atoms... they always tend to be in x+ (cations) form

b) electrophoresis i think uses the electrostatic attraction/repulsion to separate substances carrying varying charge on them... so i dont' think it should be treated as chromotography, although the principle is somewhat similar

c) spot on... in fact, even for the same element, different isotopes will (theoretically) carry different energy levels

d) there should... although as far as i am aware of, they are not widely used due to the inaccuracies comparing to AAS

e) nothing... if you don't have a sharp end point, it means you've done somethign wrong... ok it means that you did it right i guess... though if the end point is REALLY REALLY sharp, you can say that you are titrating a strong acid with a strong base (pH change from 9 to 3 in a single addition of titre... me and my friend went completely Oo when we say it)

f) spectroscopy = study of spectra... if that makes sense?!

 

[Aerlinn]

a) Hm, ok, but isnt the flame a reducing agent...?
b) I think so too, but my teacher likes to put it under the category of chromatography, strangely...
c) Isotopes... Is that due to the neutrons? I wasn't aware neutrons had any effect on the energy levels because they're neutral in charge? May be a misconception though...
d) Ok, so others are not important to know?
e) I was thinking in terms of where you have a graph, and the graph needs to have a sharp end point on it so that it's close to the equivalence point, and I understand that, but the graph--I dont know if you've come across one before or not-- the graph with its almost vertical slant just doesn't make sense.
f) Sorta. So it's supposed to say that emission SPECTRA allow large numbers of metals to be identified, yea? ^^

Thanx for all the help ^_^ *hugz*

 

[xiao1985]

a) if flame is a reducing agent then it'd make sense (though it's the first time i heard that flame is a reducing agent), because metal cation, if reduced, turns into metal atom

b) teachers are strange creatures students would never understand

c) neutrons carry mass... and the gravitational attraction of neutron with electron can change the energy a little bit... but as i said "theoretically" which means you shouldn't worry about it too much... i either want to be technically correct or just to show off i am smart (not)

d) *nod

e) vertical does make sense... in fact, most titration graph of pH vs volume of titre added should involved a vertical slant...

f) yea, if that makes you feel better =]

 

[Aerlinn]

a) Yeah. I'm not 100% sure. Just a bunsen flame, I think. Not sure about other... flames...
b) True
c) Ah... I see. But you are! Here, have a cherry *hands you one*
e) I know it should have a vertical slant, but you know how you have the pH down the vertical axis and the volume, I think, on the horizontal axis? The graph goes up steadily to the right, for instance, still it comes to a point where it just shoots up vertically, then goes back to increasing steadily to the right again. I understand the first part of the graph, where you have, as volume increases, the pH increases from acidic, aproaching 7, which makes sense because the solution is being neutralised. As soon as it hits that equivalence point though and shoots straight up, does that say that when the solution reaches a particular volume, the pH of the solution increases really, really fast over a tinsy change in volume?

 

[xiao1985]

c) why thank you *eats the cherry

e)

ohhh i see...
scenario: you are adding HCl to NaOH... you added enough so that HCl completely neutralise all NaOH... (equivalence point)... and you should note that the pH vs volume added is a sharp increase to this point...

however, because human are not perfect, you added a lil more... ie, after it reached equivalence point, you added abit more HCl...

Note now you are essentially adding a strong/perhaps concentrated acid to a neutral solution (pH 7) and you would naturally expect the pH to change drastically even if you jsut added one drop... that's why you observe yet still a sharp increase (or decrease) in pH after the equivalence point...

 

[Aerlinn]

Okies, get it all till you said:

you would naturally expect the pH to change drastically even if you jsut added one drop

Why would we naturally expect that? Puzzling...

 

[xiao1985]

hmm good question... i always assumed so... but i guess you can do mathematics and calculate it...

 

[yoakim]

That's the greatest discussion I've ever seen. So cohesively and mutually conversed.