#1


Okay lets get to it

It's a mass spectrometry HWK and i'm finding it unclear as to what it wants me to do

H [mass 1] is reacted with an excess of both Cl[mass 35] and Cl [mass 37] (the Chlorines are in ratio 3:1 hence the difference in line height on the diagram)

This thus gives me masses picked up of 35,36 and 37,38

It then wants me to draw a line on the spectrum to represent another molecular ion present in there, but what is it?! I'm confused

And then if you can make it out, what does the last part actually want me to do? I'm just finding it hard to complete

If you can help me in anyway, thank you
#5
my only guesses are maybe DCl using the minor chlorine isotope, that would give you a tiiiny peak of 39...

the peaks outside of the range are going to be all three variations of Cl2 possible... 35-35, 35-37, and 37-37... but i think your teacher forgot about H2
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#7
maybe the M-1 peak for the unreacted chlorine at 34?... not sure
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#8
^ Yeah hydrogen would be what i would have guessed at

But it says to list it on the diagram, where as it only has a range of 30-40

I may just have to pencil it on and see what he says
#9
Quote by philipisabeast


Okay lets get to it

It's a mass spectrometry HWK and i'm finding it unclear as to what it wants me to do

H [mass 1] is reacted with an excess of both Cl[mass 35] and Cl [mass 37] (the Chlorines are in ratio 3:1 hence the difference in line height on the diagram)

This thus gives me masses picked up of 35,36 and 37,38

It then wants me to draw a line on the spectrum to represent another molecular ion present in there, but what is it?! I'm confused

And then if you can make it out, what does the last part actually want me to do? I'm just finding it hard to complete

If you can help me in anyway, thank you

This is why you should pay attention in class.
Quote by add666
unreacted hydrogen

The TS said the hydrogen was reacted with excess chlorine, so there should be no unreacted hydrogen.
#10
it's a really vague question because it doesn't specify the ionization method, which produces different kinds of fragmentations...
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#11
^ In fact, we've come across this in class, and i have all of my carefully written notes around me, aswell as text books

This is the first time we have encountered this terminology and type of question, as it's designed to make us do what we can and then learn from mistakes

The answer isn't 100% obvious

EDIT: The method that we've gone over is ionisation through cathode ray, so that it becomes +ve

Would that thus mean that the answers i have to note down are all ionised?
So when i have Cl35, it would come out as a 34 and so thats what i'd note on the graph?

Actually i do think thats it
Last edited by philipisabeast at Sep 23, 2007,
#12
if anyones gunna do his who wants to do my theory of computing home work
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#13
Quote by philipisabeast
^ In fact, we've come across this in class, and i have all of my carefully written notes around me, aswell as text books

This is the first time we have encountered this terminology and type of question, as it's designed to make us do what we can and then learn from mistakes

The answer isn't 100% obvious

EDIT: The method that we've gone over is ionisation through cathode ray, so that it becomes +ve

Would that thus mean that the answers i have to note down are all ionised?
So when i have Cl35, it would come out as a 34 and so thats what i'd note on the graph?


no... i think cathode ray just pulls off an electron... so you probably wouldn't have an M-1 peak... but i'm not positive
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#14
i really don't know the answer... i'm just shooting out ideas... I'm no expert on mass spec... i'm good at using it along with other methods to identify organic compounds and that's about it.
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#16
Quote by Musicman48858
it's a really vague question because it doesn't specify the ionization method, which produces different kinds of fragmentations...

Yes, but HCl is such a simple molecule that there are a very limited number of fragments you can produce.
#18
Quote by master
verdammt, Ich dachte die hausaufgaben waren auf Deutsch. Ich kann nur Deutsch sprechen, tut mir leid...


Es tut mir leid, es ist nur an Chemie

Wow i haven't spoken german for a while

EDIT: If the cathode ray knocked 2 electrons off the Cl37 and 2 of those reacted to give a total mass of 70, and thus would have to be divided 2 on the chart [due to it being 2+ve] wouldn't it thus register on 36 ?
Last edited by philipisabeast at Sep 23, 2007,
#19
Quote by MightyAl
Yes, but HCl is such a simple molecule that there are a very limited number of fragments you can produce.


The ionization method can make it so that your Molecular Ion peak is M, M-1, M+1, and M+2, as well as sometimes actually M+15... hence, the method affecting the kinds of fragments.... I'm well aware what the structure of HCl is...
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#20
I'd pull out my Spectrometry book and look it up for you, but I left it in my lab.
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#21
Quote by philipisabeast
Es tut mir leid, es ist nur an Chemie

Wow i haven't spoken german for a while

EDIT: If the cathode ray knocked 2 electrons off the Cl37 and 2 of those reacted to give a total mass of 70, and thus would have to be divided 2 on the chart [due to it being 2+ve] wouldn't it thus register on 36 ?


possible, but unlikely...

also that wouldn't be another peak... just an increase in relative abundance of 36
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#22
^ True.

So i need 5 peaks: i have 35-38 covered which is 4

I'm still lost as to where the 5th of these are

If all fails i may have to go see my teacher tomorrow, who will probably explodion @ me
#23
i think it's still possible he's being tricky and talking about a DCl peak...

maybe atmospheric oxygen at 32?
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#25
Quote by Musicman48858
The ionization method can make it so that your Molecular Ion peak is M, M-1, M+1, and M+2, as well as sometimes actually M+15... hence, the method affecting the kinds of fragments.... I'm well aware what the structure of HCl is...

True, but since the question state the procedure has produced only 3 lines outwith the range shown, that would seem to indicate the question isn't looking for an answer at that level of detail. And answering it at that level will immediately tell the teacher it's not the TS's own work.
#26
Quote by philipisabeast
^ True.

So i need 5 peaks: i have 35-38 covered which is 4

I'm still lost as to where the 5th of these are

If all fails i may have to go see my teacher tomorrow, who will probably explodion @ me

Does the question state that the hydrogen is ALL mass #1, or could there be eaks from deuterium/tritium in there?
#27
Quote by philipisabeast
^ Could you explain what that is please?


Deuterium is a heavy isotope of hydrogen... instead of a proton and an electron, it has a proton, a neutron, and an electron... it has a super low abundance, so you probably wouldn't see it... but it has a mass of 2... I don't think it's the right answer... because practically you never see a D isotope effect in Mass Spec... but in theory... it's possible
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#28
Quote by MightyAl
True, but since the question state the procedure has produced only 3 lines outwith the range shown, that would seem to indicate the question isn't looking for an answer at that level of detail. And answering it at that level will immediately tell the teacher it's not the TS's own work.


well the M+15 isn't likely anyways... but if they were using a different method of ionization... you'd see an M-1 peak as well as the molecular ion peak for a lot of these... and that's simple enough that they might have covered it...

I'm still not positive that cathode ray doesn't produce an M-1 peak... so that you'd see one at 34 as well as the 4 he already has...


EDIT: Now that I'm remembering more about cathode ray... I think that sometimes it does knock an extra proton off too... so maybe the M-1 peak is the answer...
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Last edited by Musicman48858 at Sep 23, 2007,
#29
Quote by MightyAl
Does the question state that the hydrogen is ALL mass #1, or could there be eaks from deuterium/tritium in there?


Yeah, in the question [which is above the picture] it basically has all the info i listed and it says that the only Hydrogen there is, is with mass 1

^ And at A-level chemistry, we're just told that it creates a positive charge so no negatives
#30
Quote by Musicman48858
well the M+15 isn't likely anyways... but if they were using a different method of ionization... you'd see an M-1 peak as well as the molecular ion peak for a lot of these... and that's simple enough that they might have covered it...

I'm still not positive that cathode ray doesn't produce an M-1 peak... so that you'd see one at 34 as well as the 4 he already has...

Personally, i'm starting to think the TS should just answer that his lab gimp f*cked it up, so all the results are irrelevant.
#31
Sod it, this is ridiculous, i'll go into college early and go seek one of the chemistry staff

So to Musicman48858 and MightyAl for your time
#32
I'm a touch suprised they're talking about Mass Spec. at all at this level...
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#34
Quote by Musicman48858
I'm a touch suprised they're talking about Mass Spec. at all at this level...


It's part of the course for 15-16 year olds, this is now AS, which i think is like the US equivalent of Highschool/11th grade which is when they introduce you to the S,P and D orbital model of the atom etc

I get it all, it's just where this magical 5th line appears from thats confuses me
Last edited by philipisabeast at Sep 23, 2007,